research article free convection heat and mass transfer...
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Hindawi Publishing CorporationJournal of FluidsVolume 2013 Article ID 297493 14 pageshttpdxdoiorg1011552013297493
Research ArticleFree Convection Heat and Mass Transfer MHD Flow ina Vertical Porous Channel in the Presence of Chemical Reaction
R N Barik1 G C Dash2 and M Kar3
1 Department of Mathematics Trident Academy of Technology Infocity Bhubaneswar Odisha 751024 India2Department of Mathematics SOA University Bhubaneswar Odisha 751030 India3 Department of Mathematics Christ College Cuttack Odisha India
Correspondence should be addressed to R N Barik rnbmath22yahoocom
Received 20 May 2013 Revised 18 September 2013 Accepted 23 September 2013
Academic Editor Hideki Tsuge
Copyright copy 2013 R N Barik et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The objective of the present study is to examine the fully developed free convective MHD flow of an electrically conducting viscousincompressible fluid in a vertical porous channel under influence of asymmetric wall temperature and concentration in the presenceof chemical reaction The heat and mass transfer coupled with diffusion-thermo effect renders the present analysis interesting andcurious The analytical solution by Laplace transform technique of partial differential equations is used to obtain the expressionsfor the velocity temperature and concentration It is observed that under the influence of dominatingmass diffusivity over thermaldiffusivity with stronger Lorentz force the velocity is reduced at all points Further low rate of thermal diffusion delays the attainmentof free stream state Flow of aqueous solution in the presence of heavier species is prone to back flow
1 Introduction
In many transport processes and industrial applicationstransfer of heat and mass occurs simultaneously as a result ofcombined buoyancy effects of thermal diffusion and diffusionof chemical species Unsteady natural convection of heat andmass transfer is of great importance in designing controlsystems for modern free convection heat exchangers Morerecently Jha and Ajibade [1] have studied the heat and masstransfer aspect of the flow of a viscous incompressible fluid ina vertical channel considering the Dufour effect
Soundalgekar and Akolkar [2] studied the effect of masstransfer and free convection currents on the flow past animpulsively started infinite vertical plate and observed thatthe presence of foreign gasses in the flow domain leads toreduce the shear stress and rate of mass transfer significantly
In nature flow occurs due to density differences causedby temperature as well as chemical composition gradientsTherefore it warrants the simultaneous consideration oftemperature difference as well as concentration differencewhen heat and mass transfer occurs simultaneously It hasbeen found that an energy flux can be created not only by tem-perature gradients but by composition gradients also This is
called Dufour effect If on the other hand mass fluxes arecreated by temperature gradients it is called the Soret effect
The Soret and the Dufour effects have been found to beuseful as the Soret effect is utilized for isotope separationand in a mixture of gases of light and medium molecularweight the Dufour effect is found to be of considerable orderof magnitude such that it cannot be neglected In view ofimportance of the diffusion-thermo effect Kafoussias andWilliams [3] have studied the effects of thermal diffusionand diffusion-thermo on mixed free and forced convectiveand mass transfer boundary layer flow with temperaturedependent viscosity Jha and Singh [4] Kafoussias [5] andAlam et al [6 7] have contributed significantly to this fieldof study Recently Beg et al [8] studied chemically reactingmixed convective heat and mass transfer along inclinedand vertical plates considering Soret and Dufour effectsMore recently Dursunkaya and Worek [9] have studied thediffusion-thermo and thermal diffusion effects in transientand steady natural convections from a vertical surface
MHD flow with thermal diffusion and chemical reactionfinds numerous applications in various areas such as thermonuclear fusion liquid metal cooling of nuclear reactionsand electromagnetic casting of metals Abreu et al [10] have
2 Journal of Fluids
studied the boundary layer flows with Dufour and Soreteffects Osalusi et al [11] have worked on mixed and freeconvective heat and mass transfer of an electrically conduct-ing fluid considering Dufour and Soret effects Anghel etal [12] and Postelnicu [13] obtained numerical solutions ofchemical reacting mixed convective heat and mass transferalong inclined and vertical plates with the Soret and theDufour effects and concluded that skin friction increaseswith a positive increase in the concentration-to-thermal-buoyancy ratio parameter
The analysis of natural convection heat and mass transfernear a moving vertical plate has received much attention inrecent times due to its wide application in engineering andtechnological processes There are applications of interest inwhich combined heat and mass transfer by natural convec-tion occurs between amovingmaterial and ambientmediumsuch as the design and operation of chemical processingequipment design of heat exchangers transpiration coolingof a surface chemical vapour deposition of solid layernuclear reactor and many manufacturing processes like hotrolling hot extrusion wire drawing continuous casting andfiber drawing Gebhart and Pera [14] studied the effects ofmass transfer on a steady free convection flow past a semi-infinite vertical plate by the similarity method and it wasassumed that the concentration level of the diffusing speciesin fluid medium was very low This assumption enabledthem to neglect the diffusion-thermo and thermo-diffusioneffects as well as the interfacial velocity at the wall dueto species diffusion Following this assumption Das et al[15] investigated the effects of simultaneous heat and masstransfer on free convection flow past an infinite vertical plateunder different physical situations
Recently the unsteady MHD heat and mass transferfree convection flow of a polar fluid past a vertical movingporous plate in a porous medium with heat generation andthermal diffusion has been studied by Saxena and Dubey[16] Raveendra Babu et al [17] studied diffusion-thermoand radiation effects on MHD free convective heat and masstransfer flow past an infinite vertical plate in the presenceof a chemical reaction of first order Sudhakar et al [18]discussed chemical reaction effect on an unsteady MHD freeconvection flow past an infinite vertical accelerated plate withconstant heat flux thermal diffusion and diffusion thermo
In the present paper the flow of an electrically conductingviscous incompressible fluid in a vertical porous channelformed by two vertical parallel porous plates in the presenceof a transverse magnetic field is studied Further the masstransfer phenomena considered in this problem is associatedwith chemically reacting species The objective of the presentstudy is to extend the work of Jha and Ajibade [1] byincorporating the permeability and the magnetic field effectas well as chemical reaction on the flow heat and masstransfer phenomena
2 Mathematical Formulation
Let us consider the free convective heat and mass transferMHD flow of a viscous incompressible fluid in a verticalporous channel formedby two infinite vertical parallel porous
plates in the presence of chemical reaction A magnetic fieldof uniform strength 119861
0is applied transversely to the plate
The induced magnetic field is neglected as the magneticReynolds number of the flow is taken to be very small Theconvection current is induced due to both the temperatureand concentration differences The flow is assumed to be inthe 1199091015840-direction which is taken to be vertically upward along
the channel walls and 1199101015840-axis is taken to be normal to the
plates that are ℎ distance apartUnder the usual Boussinesqrsquos approximations the gov-
erning equations for flow are given by
1205971199061015840
1205971199051015840= ]
12059721199061015840
12059711991010158402+ 119892120573 (119879
1015840minus 1198790)
+ 119892120573lowast(1198621015840minus 1198620) minus
1205901198612
01199061015840
120588minus
]
1198701015840119901
1199061015840
1205971198621015840
1205971199051015840= 119863
12059721198621015840
12059711991010158402minus 1198701015840
119888(1198621015840minus 1198620)
1205971198791015840
1205971199051015840= 120572
12059721198791015840
12059711991010158402+ 1198631
12059721198621015840
12059711991010158402
(1)
where ] 119892 120573 120573lowast 120590 1198610 1205881198631198701015840
119888 1205721198631 and119870
1015840
119901are kinematic
viscosity acceleration due to gravity coefficient of thermalexpansion coefficient of mass expansion electrical conduc-tivity of the fluid uniformmagnetic field density of the fluidchemical molecular diffusivity the dimensional chemicalreaction parameter in the diffusion equation thermal diffu-sivity the dimensional coefficient of the diffusion-thermoeffect and the permeability of the medium respectively
Initial and boundary conditions of the problem are
1199051015840le 0 119906
1015840(1199101015840 1199051015840) = 0 119879
1015840(1199101015840 1199051015840) = 1198790 1198621015840(1199101015840 1199051015840) = 119862
0
1199051015840gt 0
1199061015840(119900 1199051015840) = 0 119879
1015840(0 1199051015840) = 119879119908 1198621015840(0 1199051015840) = 119862
119908
1199061015840(ℎ 1199051015840) = 0 119879
1015840(ℎ 1199051015840) = 1198790 1198621015840(ℎ 1199051015840) = 119862
0
(2)
We now introduce the following dimensionless quantities
119910 =1199101015840
ℎ 119905 =
1199051015840]
ℎ2 119906 =
1199061015840]
119892120573ℎ2 (119879119908
minus 1198790)
119875119903=
]
120572 119878
119888=
]
119863
119879 =1198791015840minus 1198790
119879119908
minus 1198790
119862 =1198621015840minus 1198620
119862119908
minus 1198620
119873 =120573lowast(119862119908
minus 1198620)
120573 (119879119908
minus 1198790)
119863lowast
=1198631(119862119908
minus 1198620)
120572 (119879119908
minus 1198790)
119872 =1205901198612
0ℎ2
120588]
(3)
119870119888=
119870lowast
119888ℎ2
] 119870
119901=
1198701015840
119875
ℎ2 (4)
Journal of Fluids 3
Here119875119903 119878119888119873 119863lowast119872119870
119888 and119870
119901are the Prandtl number
the Schmidt number the Sustentation parameter the Dufournumber the magnetic field parameter the chemical reactionparameter and the Porosity parameter respectively
The nondimensional form of (1) is given by
120597119906
120597119905=
1205972119906
1205971199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906
120597119862
120597119905=
1
119878119888
1205972119862
1205971199102minus 119870119888119862
120597119879
120597119905=
1
119901119903
1205972119879
1205971199102+
119863lowast
119901119903
1205972119862
1205971199102
(5)
Subject to boundary conditions
119905 le 0 119906 (119910 119905) = 0 119879 (119910 119905) = 0 119862 (119910 119905) = 0
119905 le 0 119906 (0 119905) = 0 119879 (0 119905) = 1 119862 (0 119905) = 1
119906 (1 119905) = 0 119879 (1 119905) = 0 119862 (1 119905) = 0
(6)
3 Solution of the Problem
Applying Laplace transform to (5) with boundary condition(6) we get
1198892119862
1198891199102minus 119878119888(119904 + 119870
119888) 119862 = 0
1198892119879
1198891199102minus 119904119875119903119879 = 119878
119888119863lowast(119904 + 119870
119888) 119862
(7)
119904119906 =1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 (8)
The boundary condition (6) becomes
119862 (0 119904) =1
119904 119862 (1 119904) = 0
119879 (0 119904) =1
119904 119879 (1 119904) = 0
119906 (0 119904) = 0 119906 (1 119904) = 0
(9)
Applying inverse Laplace transform to (7) and (8) subject toboundary condition (9) following Debanath and Bhatta [19]and using the formula
119871minus1
(119890minus119887radic119904+119886
119904) =
1
2119890minus119887radic119886 erfc( 119887
2radic119905minus radic119886119905)
+119890119887radic119886 erfc( 119887
2radic119905+ radic119886119905)
(10)
The solutions of (5) subject to the boundary conditions (6)are obtained by Laplace transform technique
Case 1 (119875119903
= 1 119878119888
= 1) The solutions of (5) subject to bound-ary conditions (6) are given by
119862 =
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 0 119905) minus 119891(119870
119888 119887119899radic119878119888 1 0 119905)]
119879 = 1198601
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus 119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905)
minus119891(0 119887119899radic119875119903 1 0 119905)] minus 119863
lowast119862
119906 = 1198602
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
minus 1198602
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
minus 1198603
infin
sum
119899=0
[119891(119870119888 119886119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
+ 21198604
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119872 +1
119870119901
119887119899 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
4 Journal of Fluids
minus 1198604
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 0 119905)
minus119891(119872 +1
119870119901
119887119899 1 0 119905)]
+ 1198606
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905) minus 119891(0 119887
119899radic119875119903 1 0 119905)]
(11)where 119886
119899= 2119899 + 119910 and 119887
119899= 2119899 + 2 minus 119910
The functions 119891 and erfc are given in Appendix AThe constants 119860
1 1198602 1198603 1198604 1198605 and 119860
6are given in
Appendix B
The rate of mass transfer (Sh) the rate of heat transfer(Nu) and the skin function (120591) at the walls of the channelare obtained as follows
Sherwood Number (119878ℎ) Consider
Sh0=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minusradic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 1 0 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 1 0 119905)]
Sh1=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 0 119905)]
(12)Nusselt Number (119873119906) Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
minus 119863lowastSh0
Nu1=
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 21198601radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 21198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 2 (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)]
minus 119863lowastSh1
(13)
Skin Friction (120591) Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119878119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
minus 1198602radic119878119888
infin
sum
119899=0
[119892(119870119888 2119899radic119878
119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119875119903 minus119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119875119903
minus119872 minus1
119870119901
119905)]
minus 1198603radic119875119903
infin
sum
119899=0
[119892(119870119888 2119899radic119875
119903 1 minus 119875
119903minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119875
119903 1 minus 119875
119903
minus119872 minus1
119870119901
119905)]
Journal of Fluids 5
+ 21198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119878119862
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
+ 1198605Sh0+ 1198606radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+ 119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= minus21198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 21198602radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 119905)]
minus 21198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119875119903 minus119872 minus
1
119870119901
119905)]
+ 21198603radic119875119903
infin
sum
119899=0
[119892(119870119888 (2119899 + 1)radic119875
119903 1 minus 119875
119903 minus119872
minus1
119870119901
119905)]
minus 41198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 2 (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
minus 21198606radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)] + 119860
5Sh1
(14)where the function 119892 is given in Appendix A
The mass flux (volumetric flow rate) for the problem isgiven by
119876 = int
1
0
119906 119889119910 (15)
This is computed by using the trapezoidal rule for numericalintegration
Case 2 (119875119903= 119878119888= 1) The solutions of (5) subject to boundary
conditions (6) are given by
119862 =
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
119879 =
119863lowast(1 minus 119890
minus119870119888119905)
2119870119888119905radic120587119905
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)] minus 119863
lowast119862
119906 = 1198608119862 +
119863lowast
2119905radic120587119905[
exp (minus119870119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
(119872 + (1119870119901))119870119888
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ 1198606
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
(16)where 119860
7and 119860
8are given in Appendix B
In this case the rate of mass transfer (Sh) the rate of heattransfer (Nu) and the skin frictions (120591) on the walls of thechannel are obtained as follows
Sherwood Number Consider
Sh0= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus
infin
sum
119899=0
[119892 (119870119888 2119899 1 0 119905) minus 119892 (119870
119888 2119899 + 2 1 0 119905)]
Sh1= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2
infin
sum
119899=0
[119892 (119870119888 2119899 + 1 1 0 119905)]
(17)
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
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ThermodynamicsJournal of
2 Journal of Fluids
studied the boundary layer flows with Dufour and Soreteffects Osalusi et al [11] have worked on mixed and freeconvective heat and mass transfer of an electrically conduct-ing fluid considering Dufour and Soret effects Anghel etal [12] and Postelnicu [13] obtained numerical solutions ofchemical reacting mixed convective heat and mass transferalong inclined and vertical plates with the Soret and theDufour effects and concluded that skin friction increaseswith a positive increase in the concentration-to-thermal-buoyancy ratio parameter
The analysis of natural convection heat and mass transfernear a moving vertical plate has received much attention inrecent times due to its wide application in engineering andtechnological processes There are applications of interest inwhich combined heat and mass transfer by natural convec-tion occurs between amovingmaterial and ambientmediumsuch as the design and operation of chemical processingequipment design of heat exchangers transpiration coolingof a surface chemical vapour deposition of solid layernuclear reactor and many manufacturing processes like hotrolling hot extrusion wire drawing continuous casting andfiber drawing Gebhart and Pera [14] studied the effects ofmass transfer on a steady free convection flow past a semi-infinite vertical plate by the similarity method and it wasassumed that the concentration level of the diffusing speciesin fluid medium was very low This assumption enabledthem to neglect the diffusion-thermo and thermo-diffusioneffects as well as the interfacial velocity at the wall dueto species diffusion Following this assumption Das et al[15] investigated the effects of simultaneous heat and masstransfer on free convection flow past an infinite vertical plateunder different physical situations
Recently the unsteady MHD heat and mass transferfree convection flow of a polar fluid past a vertical movingporous plate in a porous medium with heat generation andthermal diffusion has been studied by Saxena and Dubey[16] Raveendra Babu et al [17] studied diffusion-thermoand radiation effects on MHD free convective heat and masstransfer flow past an infinite vertical plate in the presenceof a chemical reaction of first order Sudhakar et al [18]discussed chemical reaction effect on an unsteady MHD freeconvection flow past an infinite vertical accelerated plate withconstant heat flux thermal diffusion and diffusion thermo
In the present paper the flow of an electrically conductingviscous incompressible fluid in a vertical porous channelformed by two vertical parallel porous plates in the presenceof a transverse magnetic field is studied Further the masstransfer phenomena considered in this problem is associatedwith chemically reacting species The objective of the presentstudy is to extend the work of Jha and Ajibade [1] byincorporating the permeability and the magnetic field effectas well as chemical reaction on the flow heat and masstransfer phenomena
2 Mathematical Formulation
Let us consider the free convective heat and mass transferMHD flow of a viscous incompressible fluid in a verticalporous channel formedby two infinite vertical parallel porous
plates in the presence of chemical reaction A magnetic fieldof uniform strength 119861
0is applied transversely to the plate
The induced magnetic field is neglected as the magneticReynolds number of the flow is taken to be very small Theconvection current is induced due to both the temperatureand concentration differences The flow is assumed to be inthe 1199091015840-direction which is taken to be vertically upward along
the channel walls and 1199101015840-axis is taken to be normal to the
plates that are ℎ distance apartUnder the usual Boussinesqrsquos approximations the gov-
erning equations for flow are given by
1205971199061015840
1205971199051015840= ]
12059721199061015840
12059711991010158402+ 119892120573 (119879
1015840minus 1198790)
+ 119892120573lowast(1198621015840minus 1198620) minus
1205901198612
01199061015840
120588minus
]
1198701015840119901
1199061015840
1205971198621015840
1205971199051015840= 119863
12059721198621015840
12059711991010158402minus 1198701015840
119888(1198621015840minus 1198620)
1205971198791015840
1205971199051015840= 120572
12059721198791015840
12059711991010158402+ 1198631
12059721198621015840
12059711991010158402
(1)
where ] 119892 120573 120573lowast 120590 1198610 1205881198631198701015840
119888 1205721198631 and119870
1015840
119901are kinematic
viscosity acceleration due to gravity coefficient of thermalexpansion coefficient of mass expansion electrical conduc-tivity of the fluid uniformmagnetic field density of the fluidchemical molecular diffusivity the dimensional chemicalreaction parameter in the diffusion equation thermal diffu-sivity the dimensional coefficient of the diffusion-thermoeffect and the permeability of the medium respectively
Initial and boundary conditions of the problem are
1199051015840le 0 119906
1015840(1199101015840 1199051015840) = 0 119879
1015840(1199101015840 1199051015840) = 1198790 1198621015840(1199101015840 1199051015840) = 119862
0
1199051015840gt 0
1199061015840(119900 1199051015840) = 0 119879
1015840(0 1199051015840) = 119879119908 1198621015840(0 1199051015840) = 119862
119908
1199061015840(ℎ 1199051015840) = 0 119879
1015840(ℎ 1199051015840) = 1198790 1198621015840(ℎ 1199051015840) = 119862
0
(2)
We now introduce the following dimensionless quantities
119910 =1199101015840
ℎ 119905 =
1199051015840]
ℎ2 119906 =
1199061015840]
119892120573ℎ2 (119879119908
minus 1198790)
119875119903=
]
120572 119878
119888=
]
119863
119879 =1198791015840minus 1198790
119879119908
minus 1198790
119862 =1198621015840minus 1198620
119862119908
minus 1198620
119873 =120573lowast(119862119908
minus 1198620)
120573 (119879119908
minus 1198790)
119863lowast
=1198631(119862119908
minus 1198620)
120572 (119879119908
minus 1198790)
119872 =1205901198612
0ℎ2
120588]
(3)
119870119888=
119870lowast
119888ℎ2
] 119870
119901=
1198701015840
119875
ℎ2 (4)
Journal of Fluids 3
Here119875119903 119878119888119873 119863lowast119872119870
119888 and119870
119901are the Prandtl number
the Schmidt number the Sustentation parameter the Dufournumber the magnetic field parameter the chemical reactionparameter and the Porosity parameter respectively
The nondimensional form of (1) is given by
120597119906
120597119905=
1205972119906
1205971199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906
120597119862
120597119905=
1
119878119888
1205972119862
1205971199102minus 119870119888119862
120597119879
120597119905=
1
119901119903
1205972119879
1205971199102+
119863lowast
119901119903
1205972119862
1205971199102
(5)
Subject to boundary conditions
119905 le 0 119906 (119910 119905) = 0 119879 (119910 119905) = 0 119862 (119910 119905) = 0
119905 le 0 119906 (0 119905) = 0 119879 (0 119905) = 1 119862 (0 119905) = 1
119906 (1 119905) = 0 119879 (1 119905) = 0 119862 (1 119905) = 0
(6)
3 Solution of the Problem
Applying Laplace transform to (5) with boundary condition(6) we get
1198892119862
1198891199102minus 119878119888(119904 + 119870
119888) 119862 = 0
1198892119879
1198891199102minus 119904119875119903119879 = 119878
119888119863lowast(119904 + 119870
119888) 119862
(7)
119904119906 =1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 (8)
The boundary condition (6) becomes
119862 (0 119904) =1
119904 119862 (1 119904) = 0
119879 (0 119904) =1
119904 119879 (1 119904) = 0
119906 (0 119904) = 0 119906 (1 119904) = 0
(9)
Applying inverse Laplace transform to (7) and (8) subject toboundary condition (9) following Debanath and Bhatta [19]and using the formula
119871minus1
(119890minus119887radic119904+119886
119904) =
1
2119890minus119887radic119886 erfc( 119887
2radic119905minus radic119886119905)
+119890119887radic119886 erfc( 119887
2radic119905+ radic119886119905)
(10)
The solutions of (5) subject to the boundary conditions (6)are obtained by Laplace transform technique
Case 1 (119875119903
= 1 119878119888
= 1) The solutions of (5) subject to bound-ary conditions (6) are given by
119862 =
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 0 119905) minus 119891(119870
119888 119887119899radic119878119888 1 0 119905)]
119879 = 1198601
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus 119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905)
minus119891(0 119887119899radic119875119903 1 0 119905)] minus 119863
lowast119862
119906 = 1198602
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
minus 1198602
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
minus 1198603
infin
sum
119899=0
[119891(119870119888 119886119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
+ 21198604
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119872 +1
119870119901
119887119899 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
4 Journal of Fluids
minus 1198604
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 0 119905)
minus119891(119872 +1
119870119901
119887119899 1 0 119905)]
+ 1198606
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905) minus 119891(0 119887
119899radic119875119903 1 0 119905)]
(11)where 119886
119899= 2119899 + 119910 and 119887
119899= 2119899 + 2 minus 119910
The functions 119891 and erfc are given in Appendix AThe constants 119860
1 1198602 1198603 1198604 1198605 and 119860
6are given in
Appendix B
The rate of mass transfer (Sh) the rate of heat transfer(Nu) and the skin function (120591) at the walls of the channelare obtained as follows
Sherwood Number (119878ℎ) Consider
Sh0=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minusradic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 1 0 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 1 0 119905)]
Sh1=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 0 119905)]
(12)Nusselt Number (119873119906) Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
minus 119863lowastSh0
Nu1=
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 21198601radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 21198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 2 (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)]
minus 119863lowastSh1
(13)
Skin Friction (120591) Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119878119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
minus 1198602radic119878119888
infin
sum
119899=0
[119892(119870119888 2119899radic119878
119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119875119903 minus119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119875119903
minus119872 minus1
119870119901
119905)]
minus 1198603radic119875119903
infin
sum
119899=0
[119892(119870119888 2119899radic119875
119903 1 minus 119875
119903minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119875
119903 1 minus 119875
119903
minus119872 minus1
119870119901
119905)]
Journal of Fluids 5
+ 21198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119878119862
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
+ 1198605Sh0+ 1198606radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+ 119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= minus21198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 21198602radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 119905)]
minus 21198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119875119903 minus119872 minus
1
119870119901
119905)]
+ 21198603radic119875119903
infin
sum
119899=0
[119892(119870119888 (2119899 + 1)radic119875
119903 1 minus 119875
119903 minus119872
minus1
119870119901
119905)]
minus 41198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 2 (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
minus 21198606radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)] + 119860
5Sh1
(14)where the function 119892 is given in Appendix A
The mass flux (volumetric flow rate) for the problem isgiven by
119876 = int
1
0
119906 119889119910 (15)
This is computed by using the trapezoidal rule for numericalintegration
Case 2 (119875119903= 119878119888= 1) The solutions of (5) subject to boundary
conditions (6) are given by
119862 =
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
119879 =
119863lowast(1 minus 119890
minus119870119888119905)
2119870119888119905radic120587119905
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)] minus 119863
lowast119862
119906 = 1198608119862 +
119863lowast
2119905radic120587119905[
exp (minus119870119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
(119872 + (1119870119901))119870119888
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ 1198606
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
(16)where 119860
7and 119860
8are given in Appendix B
In this case the rate of mass transfer (Sh) the rate of heattransfer (Nu) and the skin frictions (120591) on the walls of thechannel are obtained as follows
Sherwood Number Consider
Sh0= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus
infin
sum
119899=0
[119892 (119870119888 2119899 1 0 119905) minus 119892 (119870
119888 2119899 + 2 1 0 119905)]
Sh1= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2
infin
sum
119899=0
[119892 (119870119888 2119899 + 1 1 0 119905)]
(17)
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
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ThermodynamicsJournal of
Journal of Fluids 3
Here119875119903 119878119888119873 119863lowast119872119870
119888 and119870
119901are the Prandtl number
the Schmidt number the Sustentation parameter the Dufournumber the magnetic field parameter the chemical reactionparameter and the Porosity parameter respectively
The nondimensional form of (1) is given by
120597119906
120597119905=
1205972119906
1205971199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906
120597119862
120597119905=
1
119878119888
1205972119862
1205971199102minus 119870119888119862
120597119879
120597119905=
1
119901119903
1205972119879
1205971199102+
119863lowast
119901119903
1205972119862
1205971199102
(5)
Subject to boundary conditions
119905 le 0 119906 (119910 119905) = 0 119879 (119910 119905) = 0 119862 (119910 119905) = 0
119905 le 0 119906 (0 119905) = 0 119879 (0 119905) = 1 119862 (0 119905) = 1
119906 (1 119905) = 0 119879 (1 119905) = 0 119862 (1 119905) = 0
(6)
3 Solution of the Problem
Applying Laplace transform to (5) with boundary condition(6) we get
1198892119862
1198891199102minus 119878119888(119904 + 119870
119888) 119862 = 0
1198892119879
1198891199102minus 119904119875119903119879 = 119878
119888119863lowast(119904 + 119870
119888) 119862
(7)
119904119906 =1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 (8)
The boundary condition (6) becomes
119862 (0 119904) =1
119904 119862 (1 119904) = 0
119879 (0 119904) =1
119904 119879 (1 119904) = 0
119906 (0 119904) = 0 119906 (1 119904) = 0
(9)
Applying inverse Laplace transform to (7) and (8) subject toboundary condition (9) following Debanath and Bhatta [19]and using the formula
119871minus1
(119890minus119887radic119904+119886
119904) =
1
2119890minus119887radic119886 erfc( 119887
2radic119905minus radic119886119905)
+119890119887radic119886 erfc( 119887
2radic119905+ radic119886119905)
(10)
The solutions of (5) subject to the boundary conditions (6)are obtained by Laplace transform technique
Case 1 (119875119903
= 1 119878119888
= 1) The solutions of (5) subject to bound-ary conditions (6) are given by
119862 =
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 0 119905) minus 119891(119870
119888 119887119899radic119878119888 1 0 119905)]
119879 = 1198601
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus 119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905)
minus119891(0 119887119899radic119875119903 1 0 119905)] minus 119863
lowast119862
119906 = 1198602
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
minus 1198602
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119878119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119872 +1
119870119901
119887119899 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
minus 1198603
infin
sum
119899=0
[119891(119870119888 119886119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)
minus119891(119870119888 119887119899radic119875119903 1 minus 119875
119903 minus119872 minus
1
119870119901
119905)]
+ 21198604
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119872 +1
119870119901
119887119899 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604
infin
sum
119899=0
[119891(119870119888 119886119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(119870119888 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
4 Journal of Fluids
minus 1198604
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 0 119905)
minus119891(119872 +1
119870119901
119887119899 1 0 119905)]
+ 1198606
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905) minus 119891(0 119887
119899radic119875119903 1 0 119905)]
(11)where 119886
119899= 2119899 + 119910 and 119887
119899= 2119899 + 2 minus 119910
The functions 119891 and erfc are given in Appendix AThe constants 119860
1 1198602 1198603 1198604 1198605 and 119860
6are given in
Appendix B
The rate of mass transfer (Sh) the rate of heat transfer(Nu) and the skin function (120591) at the walls of the channelare obtained as follows
Sherwood Number (119878ℎ) Consider
Sh0=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minusradic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 1 0 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 1 0 119905)]
Sh1=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 0 119905)]
(12)Nusselt Number (119873119906) Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
minus 119863lowastSh0
Nu1=
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 21198601radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 21198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 2 (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)]
minus 119863lowastSh1
(13)
Skin Friction (120591) Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119878119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
minus 1198602radic119878119888
infin
sum
119899=0
[119892(119870119888 2119899radic119878
119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119875119903 minus119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119875119903
minus119872 minus1
119870119901
119905)]
minus 1198603radic119875119903
infin
sum
119899=0
[119892(119870119888 2119899radic119875
119903 1 minus 119875
119903minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119875
119903 1 minus 119875
119903
minus119872 minus1
119870119901
119905)]
Journal of Fluids 5
+ 21198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119878119862
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
+ 1198605Sh0+ 1198606radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+ 119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= minus21198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 21198602radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 119905)]
minus 21198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119875119903 minus119872 minus
1
119870119901
119905)]
+ 21198603radic119875119903
infin
sum
119899=0
[119892(119870119888 (2119899 + 1)radic119875
119903 1 minus 119875
119903 minus119872
minus1
119870119901
119905)]
minus 41198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 2 (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
minus 21198606radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)] + 119860
5Sh1
(14)where the function 119892 is given in Appendix A
The mass flux (volumetric flow rate) for the problem isgiven by
119876 = int
1
0
119906 119889119910 (15)
This is computed by using the trapezoidal rule for numericalintegration
Case 2 (119875119903= 119878119888= 1) The solutions of (5) subject to boundary
conditions (6) are given by
119862 =
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
119879 =
119863lowast(1 minus 119890
minus119870119888119905)
2119870119888119905radic120587119905
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)] minus 119863
lowast119862
119906 = 1198608119862 +
119863lowast
2119905radic120587119905[
exp (minus119870119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
(119872 + (1119870119901))119870119888
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ 1198606
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
(16)where 119860
7and 119860
8are given in Appendix B
In this case the rate of mass transfer (Sh) the rate of heattransfer (Nu) and the skin frictions (120591) on the walls of thechannel are obtained as follows
Sherwood Number Consider
Sh0= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus
infin
sum
119899=0
[119892 (119870119888 2119899 1 0 119905) minus 119892 (119870
119888 2119899 + 2 1 0 119905)]
Sh1= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2
infin
sum
119899=0
[119892 (119870119888 2119899 + 1 1 0 119905)]
(17)
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Superconductivity
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Journal of
Biophysics
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ThermodynamicsJournal of
4 Journal of Fluids
minus 1198604
infin
sum
119899=0
[119891(0 119886119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
minus119891(0 119887119899radic119878119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119891(119872 +1
119870119901
119886119899 1 0 119905)
minus119891(119872 +1
119870119901
119887119899 1 0 119905)]
+ 1198606
infin
sum
119899=0
[119891(0 119886119899radic119875119903 1 0 119905) minus 119891(0 119887
119899radic119875119903 1 0 119905)]
(11)where 119886
119899= 2119899 + 119910 and 119887
119899= 2119899 + 2 minus 119910
The functions 119891 and erfc are given in Appendix AThe constants 119860
1 1198602 1198603 1198604 1198605 and 119860
6are given in
Appendix B
The rate of mass transfer (Sh) the rate of heat transfer(Nu) and the skin function (120591) at the walls of the channelare obtained as follows
Sherwood Number (119878ℎ) Consider
Sh0=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minusradic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 1 0 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 1 0 119905)]
Sh1=
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 0 119905)]
(12)Nusselt Number (119873119906) Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198601radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
minus 119863lowastSh0
Nu1=
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 21198601radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 21198601radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 2 (119863lowast+ 1)radic119875
119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)]
minus 119863lowastSh1
(13)
Skin Friction (120591) Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119878119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
minus 1198602radic119878119888
infin
sum
119899=0
[119892(119870119888 2119899radic119878
119888 1 minus 119878
119888 119878119888119870119888minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 1198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 minus 119875119903 minus119872 minus
1
119870119901
119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 minus 119875119903
minus119872 minus1
119870119901
119905)]
minus 1198603radic119875119903
infin
sum
119899=0
[119892(119870119888 2119899radic119875
119903 1 minus 119875
119903minus 119872 minus
1
119870119901
119905)
+ 119892(119870119888 (2119899 + 2)radic119875
119903 1 minus 119875
119903
minus119872 minus1
119870119901
119905)]
Journal of Fluids 5
+ 21198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119878119862
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
+ 1198605Sh0+ 1198606radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+ 119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= minus21198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 21198602radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 119905)]
minus 21198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119875119903 minus119872 minus
1
119870119901
119905)]
+ 21198603radic119875119903
infin
sum
119899=0
[119892(119870119888 (2119899 + 1)radic119875
119903 1 minus 119875
119903 minus119872
minus1
119870119901
119905)]
minus 41198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 2 (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
minus 21198606radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)] + 119860
5Sh1
(14)where the function 119892 is given in Appendix A
The mass flux (volumetric flow rate) for the problem isgiven by
119876 = int
1
0
119906 119889119910 (15)
This is computed by using the trapezoidal rule for numericalintegration
Case 2 (119875119903= 119878119888= 1) The solutions of (5) subject to boundary
conditions (6) are given by
119862 =
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
119879 =
119863lowast(1 minus 119890
minus119870119888119905)
2119870119888119905radic120587119905
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)] minus 119863
lowast119862
119906 = 1198608119862 +
119863lowast
2119905radic120587119905[
exp (minus119870119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
(119872 + (1119870119901))119870119888
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ 1198606
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
(16)where 119860
7and 119860
8are given in Appendix B
In this case the rate of mass transfer (Sh) the rate of heattransfer (Nu) and the skin frictions (120591) on the walls of thechannel are obtained as follows
Sherwood Number Consider
Sh0= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus
infin
sum
119899=0
[119892 (119870119888 2119899 1 0 119905) minus 119892 (119870
119888 2119899 + 2 1 0 119905)]
Sh1= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2
infin
sum
119899=0
[119892 (119870119888 2119899 + 1 1 0 119905)]
(17)
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
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Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
Journal of Fluids 5
+ 21198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119878119862
infin
sum
119899=0
[119892 (119870119888 2119899radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)
+ 119892 (119870119888 (2119899 + 2)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 1198604radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)
+119892 (0 (2119899 + 2)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
+ (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+ 119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
+ 1198605Sh0+ 1198606radic119875119903
infin
sum
119899=0
[119892 (0 2119899radic119875119903 1 0 119905)
+ 119892 (0 (2119899 + 2)radic119875119903 1 0 119905)]
1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= minus21198602
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119878119888 119878119888119870119888
minus119872 minus1
119870119901
119905)]
+ 21198602radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 1 minus 119878
119888 119878119888119870119888
minus119872 119905)]
minus 21198603
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 minus 119875119903 minus119872 minus
1
119870119901
119905)]
+ 21198603radic119875119903
infin
sum
119899=0
[119892(119870119888 (2119899 + 1)radic119875
119903 1 minus 119875
119903 minus119872
minus1
119870119901
119905)]
minus 41198604
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119878119888
infin
sum
119899=0
[119892 (119870119888 (2119899 + 1)radic119878
119888 119875119903minus 119878119888 119878119888119870119888 119905)]
+ 21198604radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 119875119903minus 119878119888 119878119888119870119888 119905)]
minus 2 (1198605minus 1198606)
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
minus 21198606radic119875119903
infin
sum
119899=0
[119892 (0 (2119899 + 1)radic119875119903 1 0 119905)] + 119860
5Sh1
(14)where the function 119892 is given in Appendix A
The mass flux (volumetric flow rate) for the problem isgiven by
119876 = int
1
0
119906 119889119910 (15)
This is computed by using the trapezoidal rule for numericalintegration
Case 2 (119875119903= 119878119888= 1) The solutions of (5) subject to boundary
conditions (6) are given by
119862 =
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
119879 =
119863lowast(1 minus 119890
minus119870119888119905)
2119870119888119905radic120587119905
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ (119863lowast+ 1)
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)] minus 119863
lowast119862
119906 = 1198608119862 +
119863lowast
2119905radic120587119905[
exp (minus119870119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
(119872 + (1119870119901))119870119888
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[119886119899exp(minus
1198862
119899
4119905) minus 119887119899exp(minus
1198872
119899
4119905)]
+ 1198606
infin
sum
119899=0
[119891 (0 119886119899 1 0 119905) minus 119891 (0 119887
119899 1 0 119905)]
(16)where 119860
7and 119860
8are given in Appendix B
In this case the rate of mass transfer (Sh) the rate of heattransfer (Nu) and the skin frictions (120591) on the walls of thechannel are obtained as follows
Sherwood Number Consider
Sh0= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus
infin
sum
119899=0
[119892 (119870119888 2119899 1 0 119905) minus 119892 (119870
119888 2119899 + 2 1 0 119905)]
Sh1= minus
120597119862
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 2
infin
sum
119899=0
[119892 (119870119888 2119899 + 1 1 0 119905)]
(17)
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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FluidsJournal of
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Superconductivity
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Biophysics
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ThermodynamicsJournal of
6 Journal of Fluids
Nusselt Number Consider
Nu0= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= minus119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
minus (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
+ 119863lowastSh0
Nu1= minus
120597119879
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
=119863lowast[1 minus exp (minus119870
119888119905)]
2119870119888119905radic120587119905
times [2
infin
sum
119899=0
exp(minus(2119899 + 1)
2
4119905)
minus1
119905
infin
sum
119899=0
(2119899 + 1)2 exp(minus
(2119899 + 1)2
4119905)]
+ 2 (119863lowast+ 1)
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)] minus 119863lowastSh1
(18)
Skin Friction Consider
1205910= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=0
= 1198608Sh0+
119863lowast
2119905radic120587119905
times [exp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
+1
119870119888(119872 + (1119870
119901))
minusexp (minus119872119905)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
]
times [
infin
sum
119899=0
exp(minus1198992
119905) + exp(minus
(119899 + 1)2
119905)
minus2
119905
infin
sum
119899=0
1198992 exp(minus
1198992
119905)
+(119899 + 1)2 exp(minus
(119899 + 1)2
119905)]
+ 1198606
infin
sum
119899=0
[119892 (0 2119899 1 0 119905) + 119892 (0 2119899 + 2 1 0 119905)]
minus 1198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 1 0 119905)
+119892(119872 +1
119870119901
2119899 + 2 1 0 119905)]
(19)1205911= minus
120597119906
120597119910
10038161003816100381610038161003816100381610038161003816119910=1
= 1198608Sh1+
119863lowast
119905radic120587119905
times [
exp (minus119872 minus (1119870119901)) 119905
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
minus1
119870119888(119872 + (1119870
119901))
minusexp (minus119870
119888119905)
119870119888(119870119888minus 119872 minus (1119870
119901))
]
times
infin
sum
119899=0
[exp(minus(2119899 + 1)
2
119905)
minus2(2119899 + 1)
2
119905exp(minus
(2119899 + 1)2
119905)]
minus 21198606
infin
sum
119899=0
[119892 (0 2119899 + 1 1 0 119905)]
times 21198607
infin
sum
119899=0
[119892(119872 +1
119870119901
2119899 + 1 1 0 119905)]
(20)
Steady State Setting 120597119906120597t = 0 120597119879120597t = 0 and 120597119862120597t = 0 in(5) the steady state of the problem is obtained as
1198892119906
1198891199102+ 119873119862 + 119879 minus (119872 +
1
119870119901
)119906 = 0
1198892119862
1198891199102minus 119878119888119870119888119862 = 0
1198892119879
1198891199102+ 119863lowast 1198892119862
1198891199102= 0
(21)
The solutions of (21) subject to boundary conditions (6)are given by
119862 =sinh (radic119878
119888119870119888(1 minus 119910))
sinh (radic119878119888119870119888)
119879 = (119863lowast+ 1) (1 minus 119910) minus 119863
lowast119862
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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FluidsJournal of
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Superconductivity
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Physics Research International
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Computational Methods in Physics
Journal of
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Soft MatterJournal of
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Volume 2014
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PhotonicsJournal of
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Journal of
Biophysics
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ThermodynamicsJournal of
Journal of Fluids 7
Curve
I 04 05 022 2 2 18 2 100
II 02 05 022 2 2 18 2 100
III 04 2 022 2 2 18 2 100
IV 04 05 03 2 2 18 2 100
V 04 05 022 1 2 18 2 100
VI 04 05 022 2 4 18 2 100
VII 04 05 022 2 2 2 2 100
VIII 04 05 022 2 2 18 4 100
IX 04 05 022 2 2 18 2 05
X Steadystate 05 022 2 4 2 100
04
02
0
minus02
minus04
minus06
minus08
minus1
u
0 02 04 06 08 1
II
IVI
V III
IXVII
VIII
IV
X
y
t M Sc Kc N Pr KpDlowast
mdash
Figure 1 Velocity profile
119906 = 1198609
sinhradic(119872 + (1119870119901)) (1 minus 119910)
sinhradic119872 + (1119870119901)
+ 1198605119862 + 119860
6(1 minus 119910)
(22)
where 1198609is given in Appendix B
In this case the Sherwood number (Sh) the Nusseltnumber (Nu) and the skin friction (120591) are given by thefollowing
Sherwood Number (119878ℎ) Consider
Sh0= radic119878119888119870119888cothradic119878
119888119870119888
Sh1= radic119878119888119870119888cosechradic119878
119888119870119888
(23)
Nusselt Number (119873119906) Consider
Nu0= 119863lowast+ 1 + 119863
lowastSh0
Nu1= minus (119863
lowast+ 1) minus 119863
lowastSh1
(24)
Skin Friction (120591) Consider
1205910= minus1198609radic119872 +
1
119870119901
cothradic119872 +1
119870119901
+ 1198605Sh0minus 1198606
1205911=
1198609radic119872 + (1119870
119901)
sinhradic119872 + (1119870119901)
minus 1198605Sh1+ 1198606
(25)
Mass Flux Consider
119876 = 1198609radic119872 +
1
119870119901
coshradic119872 + (1119870119901) minus 1
sinhradic119872 + (1119870119901)
+1198605
radic119878119888119870119888
coshradic119878119888119870119888minus 1
sinhradic119878119888119870119888
+1198606
2
(26)
4 Results and Discussion
Computations have been carried out by assigning the valuesto the pertinent parameters characterising the fluids ofpractical interest The flow phenomenon is characterized bymagnetic parameter (119872) chemical reaction parameter (119870
119888)
sustentation parameter (119873) Dufour number (119863lowast) Schmidtnumber (119878
119888) Prandtl number (119875
119903) and porosity parameter
(119870119901) The effects of various parameters on velocity tempera-
ture and concentration profiles are shown graphically and intabulated form for Sherwood number (Sh) Nusselt number(Nu) and skin friction (120591)
The particular case without magnetic field and porosity(119872 = 0 119870
119901rarr infin) can be obtained from (8) which is in
good agreement with the work reported earlier [1]Another interesting point to note is that diffusion in
aqueous solution that is for higher values of 119878119888gives rise to
oscillations in the velocity as well as temperature field in thepresence of chemical reaction parameter (119870
119888)
Figure 1 depicts the velocity profile for various values ofpertinent parameters characterising flow fieldsThe common
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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FluidsJournal of
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Superconductivity
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Soft MatterJournal of
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Biophysics
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ThermodynamicsJournal of
8 Journal of Fluids
1000
500
0
minus500
minus1000
minus1500
minus2000
u
0 02 04 06 08 1 12y
Sc = 5 Kc = 0 Kp = 100
Sc = 150 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 100
Sc = 200 Kc = 0 Kp = 05
Figure 2 Velocity profile for 119905 = 04 119872 = 05 119873 = 2 119875119903= 7 and 119863
lowast= 2
0 02 04 06 08 1 12y
035
03
025
02
015
01
005
0
u
VIII
VI
I II III VII
V
IV
Curve
I 05 100 1 2 2 100
II 05 022 2 2 2 100
III 05 152 1 2 2 100
IV 05 022 2 2 2 05
V 2 022 2 2 2 100
VI 05 022 2 2 30 100
VII 05 03 1 2 2 100VIII 05 022 2 4 2 100
M Sc Kc N KpDlowast
Figure 3 Velocity profile (steady state)
feature of the profiles is parabolicThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X) in caseof steady state as well as 119905 le 03 the velocity profiles remainpositive throughout the flow fieldThis is evident from curvesII and X (119905 = 02 Curve II the steady state curve X)Thus it isconcluded that the time span plays a vital role for engenderingback flow (Curve I and Curve II)
Further magnetic parameter (119872) chemical reactionparameter (119870
119888) sustentation parameter (119873) and porosity
parameter (119870119901) decrease the velocity |119906| at all points In
all other cases such as 119878119888 119875119903 and 119863
lowast the reverse effectis observed If the mass diffusivity becomes greater thanthe thermal diffusivity (ie 119873 the sustentation parametergt10) then the velocity decreases Moreover with the stronger
magnetic field Lorentz force also reduces the velocity fieldwhich is in conformity with the result of Cramer and Pai [20]
An increase in 119875119903leads to decrease in the velocity which
suggests that low rate of thermal diffusion leads to increase inthe velocity boundary layer thickness
Figure 2 depicts the velocity distribution in the absence ofchemical reaction It is noteworthy to observe that the backflow occurs for higher values of 119878
119888 that is 119878
119888= 150 and
119878119888
= 200 and the permeability of the medium representingthe diffusion in aqueous solution in the presence of constantmagnetic field and Dufour effect Further it is to mentionthat for 119878
119888lt 10 and 119870
119888= 00 no velocity profile could be
graphedpresented Further it is to note that heavier speciesthat is with increasing 119878
119888lead to flow reversal It is most
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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FluidsJournal of
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Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Soft MatterJournal of
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PhotonicsJournal of
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Journal of
Biophysics
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ThermodynamicsJournal of
Journal of Fluids 9
CurveI 04 022 20 700II 04 022 00 700III
III
04 00 700IV 04 20 700V 02 20 700VI 04 022 00 071VII 04 022 02 071VII 04 00 071IX 04 02 071X 02 02 071
t Sc Kc Pr
6
5
4
3
2
1
00 02 04 06 08 1
y
T
V I II
IV
VI-X
WaterAir
030030030
030030030
Figure 4 Temperature profile for 119863lowast= 20 119875
119903= 70 (water) and 119875
119903= 071 (air)
0
02
04
06
08
1
12
0 02 04 06 08 1
T
y
IIII
II
Curve t Kc
I 04 20II 04 10III 02 20
Figure 5 Temperature profile (119875119903= 1 119878
119888= 1)
interesting to note that in the presence of destructive reactionthat is 119870
119888gt 0 higher value of 119878
119888leads to oscillatory flow
and in case of diffusion in the aqueous solution it leads toback flow Thus this suggests that the back flow is preventedby diffusing lighter species which is in conformity with theresults reported earlier by Pop [21] Hossain andMohammad[22] and Rath et al [23]
It is also remarked that when 119878119888varies from0 to 5 the back
flow is prevented in the absence of chemical reaction But inthe presence of heavier species the sharp fall of velocity is wellmarked
Figure 3 exhibits the steady state velocity profiles indicat-ing no back flow irrespective of higher or lower value of masstransfer coefficient and Dufour effect
On careful observation it is revealed that for highervalues of Dufour number119863lowast (curve VI) sustentation param-eter 119873 (Curve VIII) magnetic parameter 119872 (Curve V) andporosity parameter 119870
119901(Curve IV) steady state velocity is
effected significantly whereas variation in reaction parameter
and Schmidt number produces no change Thus it is impor-tant to note that mass transfer phenomena with chemicalreaction does not affect the steady flow significantly butincrease in119872 119873119863lowast and119870
119901 decrease the velocity increase
the velocity increase the velocity and decrease the velocityrespectively It may be inferred that magnetic parameterporosity parameter andDufour effect produce the same effectirrespective of steady or unsteady state except for sustentationparameter
Figures 4 5 and 6 present the temperature distribution Itis seen that for an increase in destructive reaction parameter(119870119888gt 0) temperature increases whereas increase in 119875
119903 119905 and
119878119888reduces the temperature at all points for 119875
119903= 70 (water)
when 119910 lt 07 It is noted that the slow rate of diffusion leavesthe heat energy spread in the fluidmass and it is enhanced forheavier species
It is observed in case of 119875119903= 071 (air) that the tempera-
ture falls sharply at all points with almost linear distributionregardless of other parameters Thus it may be pointed out
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
10 Journal of Fluids
002040608
1121416
0 02 04 06 08 1
T
y
IV
II
I
III
Curve Sc Kc Dlowast
I 022 2 2II 030 2 2III 022 1 2IV 022 2 30
Figure 6 Temperature profile (steady state)
CurveI 04 100 0II 04 617 0III 04 100 2IV 04 617 2V 02 100 2
t Kc
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
I
III
II IVV
y
Sc
Figure 7 Concentration profile
0010203040506070809
1
0 02 04 06 08 1
C
y
III
III
Curve t Kc
I 04 20II 04 10III 02 20
Figure 8 Concentration profile (119878119888= 1)
that thermal diffusivity property of the fluid plays a vitalrole in controlling the temperature distribution and hencecontributing to thermal boundary layer thickness
Figure 5 also exhibits the temperature distribution when119875119903
= 1 and 119878119888
= 1 which means that thermal diffusivityand mass diffusivity are at par This contributes to the uni-form variationdecrease in temperature Increase in reactionparameter gives rise to increase in temperature whereasallowing for a large span of time reduces it
minus02
0
02
04
06
08
1
0 02 04 06 08 1
C
y
Curve Sc Kc
I 100 2II 617 1III 617 2
Figure 9 Concentration profile (steady state)
Figure 6 presents the nonlinearity distribution of tem-perature due to high value of 119863
lowast that is for large Dufoureffect Thus sharp rise and fall of temperature is due to lowdiffusivity and high Dufour effect
Figures 7 8 and 9 exhibit the concentration variation inthe flow domain Sharp fall of concentration is indicated inFigures 7 and 9 along with mass absorption near the plate forvery high value of 119878
119888(ie 119878
119888= 617) This means that heavier
species give rise to sharp fall of concentration accelerating theprocess ofmass diffusionwhereas in case of lighter species thevariation is smooth
Skin friction plays an important role in flow characteris-tics It measures the frictional forces encountered at the solidsurfaces due to themotion of the fluid One striking feature ofthe entries of the skin friction in Table 1 in case of unsteadymotion is that the skin frictions bear same sign in case oflower and upper plate Further on careful observation it isrevealed that at the lower plate all are negative for 119905 = 04
except for the case when 119905 = 02 Thus it may be concludedthat time span plays an important role tomodify the frictionaldrag due to shear stress at the plates
Moreover from (18)-(19) it is clear that the Prandtl num-ber (119875
119903) has no role to play to affect the velocity temperature
and concentration fields in the steady flow and hence the skin
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
Journal of Fluids 11
Table 1 Skin friction (unsteady case)
Sl no 119905 119872 119878119888
119870119888
119873 119875119903
119863lowast
119870119901
1205910
1205911
1 04 05 022 2 2 18 2 100 minus137638 minus031532 02 05 022 2 2 18 2 100 0649408 04663083 04 2 022 2 2 18 2 100 minus040403 minus0122794 04 05 03 2 2 18 2 100 minus290421 minus098275 04 05 022 1 2 18 2 100 minus046631 minus0158386 04 05 022 2 4 18 2 100 minus091633 minus0286757 04 05 022 2 2 2 2 100 minus166428 minus033468 04 05 022 2 2 18 4 100 minus224604 minus0344339 04 05 022 2 2 18 2 05 minus125513 minus02425
Table 2 Skin friction (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
1205910
1205911
1 05 022 2 2 2 100 1732053 09325152 2 022 2 2 2 100 166425 07954363 05 03 2 2 2 100 1732052 09325154 05 022 1 2 2 100 173205 09325155 05 022 2 4 2 100 1664279 08692876 05 022 2 2 4 100 2144507 13763827 05 022 2 2 2 05 142312 0524363
Table 3 Nusselt number
Sl no 119905 119878119888
119870119888
119875119903
119863lowast Nu
0Nu1
1 04 022 2 700 2 minus137638192 minus11503684072 02 022 2 700 2 minus2674621494 minus12130970043 04 030 2 700 2 minus1327044822 minus11106125154 04 022 0 700 2 minus1455009029 minus11917535935 04 022 2 071 2 0113935608 minus01139356086 04 022 2 700 4 minus1569685558 minus1279941632
friction In case of unsteady flow as 119875119903increases the shearing
stress increases at both the platesConsidering Tables 1 and 2 for both steady and unsteady
cases it is concluded that an increase in magnetic param-eter porosity parameter and sustentation parameter leadsto reduce the magnitude of frictional drag at both platesMoreover an increase in 119878
119888 119870119888 and 119863
lowast leads to enhance thefrictional drag at the plates for steady and unsteady flow
Physically we may interpret the above results as followsLorentz force and sustentation parameter that is ratios
of buoyancy effects due to temperature and concentrationdifferences reduce the frictional drag which agrees well withthe established result reported earlier Moreover presence ofheavier species and exothermic reaction and Dufour effectenhance the magnitude of the shearing stress at both plates
From Table 3 it is seen that an increase in 119905 119878119888 and 119870
119888
leads to decrease the Nusselt number at both plates Oneinteresting point is that rate of heat transfer remains negativefor all the parameters at both the plates for aqueous solution119875119903= 70 but in case of air that is 119875
119903= 071 Nusselt number
is positive at the lower plate and negative at the upper plate
Table 4 Sherwood number
Sl no 119905 119878119888
119870119888
Sh0
Sh1
1 04 100 2 59757644 minus06128007882 02 100 2 6313751515 0158384443 04 617 2 7026366229 04705642814 02 100 0 567128182 minus0466307658
Table 4 presents the variation of mass transfer for variousvalues of 119905 119878
119888 and 119870
119888 It is seen that an increase in chemical
reaction parameter119870119888increases themass transfer at the lower
plate and decreases it at the other Further it is to note thatSherwood number at both the plates increases as 119878
119888increases
that is for heavier speciesmass transfer increases at the platesThe effect of increase in time span is to reduce the rate ofmasstransfer at both plates
Tables 5 and 6 show the effects of various parameters onmass flux both for unsteady and steady cases respectivelyFrom Table 5 it is observed that mass flux increases with the
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
12 Journal of Fluids
Table 5 Mass flux (unsteady case)
Sl no 119905 119872 119878119888
119870c 119873 119875119903
119863lowast
119870119901
119876
1 04 05 022 2 2 18 2 100 01978362 02 05 022 2 2 18 2 100 01765723 04 2 022 2 2 18 2 100 00576554 04 05 03 2 2 18 2 100 05684755 04 05 022 1 2 18 2 100 00911936 04 05 022 2 4 18 2 100 01666677 04 05 022 2 2 2 2 100 02649398 04 05 022 2 2 18 4 100 03645839 04 05 022 2 2 18 2 05 0034241
Table 6 Mass flux (steady case)
Sl no 119872 119878119888
119870119888
119873 119863lowast
119870119901
119876
1 05 022 2 2 2 100 01190522 2 022 2 2 2 100 01042073 05 03 2 2 2 100 01190524 05 022 1 2 2 100 01190525 05 022 2 4 2 100 01950776 05 022 2 2 4 100 01223927 05 022 2 2 2 05 0094632
increase in the values in 119878119888 119870119888 119875119903 and 119863
lowast but the reverseeffect is observed in case of 119905119872119873 and119870
119901when the motion
is unsteady Hence it is concluded that in case of unsteadymotion more flux fluid was experienced with heavier specieshaving low thermal diffusivity and increasing Dufour effectin the presence of constructive chemical reaction
Now if we analyse the steady casewe observe that moreflux is measured with higher value of 119873 and 119863
lowast whereas thereverse effect is observed in case of 119872 and 119870
119901 In case of 119878
119888
and 119870119888there is no significant effect on mass flux
Comparing both cases steady and unsteady motion it isobserved that an increase in 119870
119888and 119863
lowast gives rise to higherflux whereas magnetic field yields less amount of flux
5 Conclusion
(i) Under the influence of dominating mass diffusivityover thermal diffusivity with stronger Lorentz forcethe velocity is reduced at all points of the channel
(ii) Low rate of thermal diffusion leads to increase thethickness of boundary layer
(iii) Diffusion of heavier species leads to flow reversal Itis well marked in case of aqueous solution Flow ofaqueous solution in the presence of heavier species isprone to back flow
(iv) Destructive reaction in the presence of heavier speciesleads to oscillatory flow
(v) In case of steady state no back flow occurs irrespec-tive of high or low value of mass transfer coefficientand Dufour effects
(vi) Sharp rise and fall of temperature is the outcome oflow diffusivity and high Dufour effects
(vii) Dufour effect and chemical reaction rate in the pres-ence of heavier species enhance the frictional drag
(viii) Heat transfer bears same sign at both the plates in thepresence of aqueous solution but in case of air it is ofopposite sign
(ix) Mass transfer increases at both plates due to the pres-ence of heavier species but it reduces with increasingtime span
(x) In case of unsteady motion more flux of fluid isexperienced due to heavier species with low thermaldiffusivity Dufour effect enhances the flux both insteady and unsteady motion
Appendices
A
The complementary error function is given by
erfc (x) =2
radic120587int
infin
119909
119890minus1205822
119889120582
119891 (1199091 1199092 1199093 1199094 1199095)
=1
2exp(
11990941199095
1199093
)
times [exp(minus1199092radic
1199094
1199093
+ 1199091)
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
Journal of Fluids 13
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)
+ exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)]
119892 (1199091 1199092 1199093 1199094 1199095)
=1
2radic
1199094
1199093
+ 1199091exp(
11990941199095
1199093
)
times [exp(1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
+ radic(1199094
1199093
+ 1199091)1199095)
minus exp(minus1199092radic
1199094
1199093
+ 1199091)
times erfc( 1199092
2radic1199095
minus radic(1199094
1199093
+ 1199091)1199095)]
minus2
radic120587exp(minus(
1199092
3
41199095
+ 11990911199095))
(A1)
B
1198601= minus119863lowast[
119878119888
119875119903minus 119878119888
+ 119875119903minus 119878119888]
1198602= minus
1 minus 119878119888
119878119888119870119888minus 119872 minus (1119870
119901)
times [119873 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198603=
1 minus 119875119903
119872 + (1119870119901)
times [1 +
119878119888119863lowast(119870119888minus 119872 minus (1119870
119901))
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
]
1198604=
119863lowast119875119903(119875119903minus 119878119888)
119878119888119870119888(1 minus 119875
119903) + (119872 + (1119870
119901)) (119875119903minus 119878119888)
1198605=
119863lowastminus 119873
119878119888119870119888minus 119872 minus (1119870
119901)
1198606=
119863lowast+ 1
119872 + (1119870119901)
1198607=
119870119888(119863lowast+ 1) minus (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119870119888minus 119872 minus (1119870
119901))
1198608=
119863lowastminus 119873
119870119888minus 119872 minus (1119870
119901)
1198609=
minus119878119888119870119888(119863lowast+ 1) + (119872 + (1119870
119901)) (119873 + 1)
(119872 + (1119870119901)) (119878119888119870119888minus 119872 minus (1119870
119901))
References
[1] B K Jha and A O Ajibade ldquoFree convection heat and masstransfer flow in a vertical channel with the Dufour effectrdquo Jour-nal of Process Mechanical Engineering vol 224 no 2 pp 91ndash1012010
[2] VM Soundalgekar and S P Akolkar ldquoEffects of free convectioncurrents and mass transfer on flow past a vertical oscillatingplaterdquoAstrophysics and Space Science vol 89 no 2 pp 241ndash2541983
[3] N G Kafoussias and E W Williams ldquoThermal-diffusion anddiffusion-thermo effects on mixed free-forced convective andmass transfer boundary layer flow with temperature dependentviscosityrdquo International Journal of Engineering Science vol 33no 9 pp 1369ndash1384 1995
[4] B K Jha and A K Singh ldquoSoret effects on free-convection andmass transfer flow in the stokes problem for a infinite verticalplaterdquo Astrophysics and Space Science vol 173 no 2 pp 251ndash255 1990
[5] N G Kafoussias ldquoMHD thermal-diffusion effects on free-con-vective and mass-transfer flow over an infinite vertical movingplaterdquo Astrophysics and Space Science vol 192 no 1 pp 11ndash191992
[6] M S Alam M M Rahman and M A Samad ldquoDufour andSoret effects on unsteady MHD free convection and masstransfer flow past a vertical porous plate in a porous mediumrdquoNonlinear Analysis Modelling and Control vol 11 no 3 pp 217ndash226 2006
[7] M S AlamMM RahmanM Ferdous KMaino EMureithiand A Postelnicu ldquoDiffusion-thermo and thermal-diffusioneffects on free convective heat andmass transfer flow in a porousmedium with time dependent temperature and concentrationrdquoInternational Journal of Applied Engineering Research vol 2 no1 pp 81ndash96 2007
[8] O A Beg T A Beg A Y Bakier andV R Prasad ldquoChemically-reactingmixed convective heat andmass transfer along inclinedand vertical plates with soret and Dufour effects numericalsolutionrdquo International Journal of Applied Mathematics andMechanics vol 5 no 2 pp 39ndash57 2009
[9] Z Dursunkaya and W M Worek ldquoDiffusion-thermo andthermal-diffusion effects in transient and steady natural con-vection from a vertical surfacerdquo International Journal of Heatand Mass Transfer vol 35 no 8 pp 2060ndash2065 1992
[10] C R A Abreu M F Alfradique and A S Telles ldquoBoundarylayer flows with Dufour and Soret effects I forced and naturalconvectionrdquo Chemical Engineering Science vol 61 no 13 pp4282ndash4289 2006
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
14 Journal of Fluids
[11] E Osalusi J Side and R Harris ldquoThermal-diffusion and diffu-sion-thermo effects on combined heat and mass transfer of asteadyMHD convective and slip flow due to a rotating disk withviscous dissipation and Ohmic heatingrdquo International Commu-nications in Heat and Mass Transfer vol 35 no 8 pp 908ndash9152008
[12] M Anghel H S Takhar and I Pop ldquoDufour and Soret effectson free convection boundary layer over a vertical surfaceembedded in a porous mediumrdquo Studia Universitatis Babes-Bolyai Matematica vol 11 no 4 pp 11ndash21 2000
[13] A Postelnicu ldquoInfluence of a magnetic field on heat and masstransfer by natural convection from vertical surfaces in porousmedia considering Soret and Dufour effectsrdquo InternationalJournal of Heat andMass Transfer vol 47 no 6-7 pp 1467ndash14722004
[14] B Gebhart and L Pera ldquoThe nature of vertical natural con-vection flows resulting from the combined buoyancy effects ofthermal and mass diffusionrdquo International Journal of Heat andMass Transfer vol 14 no 12 pp 2025ndash2050 1971
[15] U N Das R Deka and V M Soundalgekar ldquoEffects of masstransfer on flowpast an impulsively started infinite vertical platewith constant heat flux and chemical reactionrdquo Forschung imIngenieurwesen vol 60 no 10 pp 284ndash287 1994
[16] S S Saxena and G K Dubey ldquoUnsteady MHD heat and masstransfer free convection flow of a polar fluid past a verticalmoving porous plate in a porous medium with heat generationand thermal diffusionrdquo Advances in Applied Science Researchvol 2 no 4 pp 259ndash278 2011
[17] K Raveendra Babu A G Vijaya Kumar and S V K VarmaldquoDiffusion-thermo and radiation effects on MHD free convec-tive heat and mass transfer flow past an infinite vertical plate inthe presence of a chemical reaction of first orderrdquo Advances inApplied Science Research vol 3 no 4 pp 2446ndash2462 2012
[18] K Sudhakar R Srinibasa Raju and M Rangamma ldquoChemicalreaction effect on an unsteady MHD free convection flow pastan infinite vertical accelerated plate with constant heat fluxthermal diffusion and diffusion thermordquo International Journalof Modern Engineering Research vol 2 no 5 pp 3329ndash33392012
[19] L Debanath andD Bhatta Integral Transforms andTheir Appli-cations Applications of Laplace Transforms Chapman andHallCRC Taylor and Francies Group London UK 2007
[20] K R Cramer and S I PaiMagnetofluid Dynamics for Engineersand Applied Physics McGraw-Hill New York NY USA 1973
[21] I Pop ldquoEffect of Hall current on hydromagnetic flow near anaccelerated platerdquo International Journal of Physics and Mathe-matical Sciences vol 5 p 375 1971
[22] M A Hossain and K Mohammad ldquoEffect of hall current onhydromagnetic free convection flow near an accelerated porousplaterdquo Japanese Journal of Applied Physics vol 27 no 8 pp 1531ndash1535 1988
[23] P K Rath G C Dash and A K Patra ldquoEffect of Hallcurrent and chemical reaction on MHD flow along an expo-nentially accelerated porous flat plate with internal heat absorp-tiongenerationrdquo Proceedings of the National Academy of Sci-ences India A vol 80 no 4 pp 295ndash308 2010
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
High Energy PhysicsAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
FluidsJournal of
Atomic and Molecular Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in Condensed Matter Physics
OpticsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstronomyAdvances in
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Superconductivity
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Statistical MechanicsInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GravityJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
AstrophysicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Physics Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Solid State PhysicsJournal of
Computational Methods in Physics
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Soft MatterJournal of
Hindawi Publishing Corporationhttpwwwhindawicom
AerodynamicsJournal of
Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
PhotonicsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Biophysics
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
ThermodynamicsJournal of