ccb 3033 advanced transport processes newww

7/24/2019 Ccb 3033 Advanced Transport Processes Newww

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CCB 3033 ADVANCED TRANSPORT PROCESSES

CFD PROJECT

CFD SIMULATION OF HEAT EXCHANGE

EQUIPMENT

GROUP MEMBERS: ID NO:

HEMALA PANNEERCHELVAM 16084

Date ! S"#$%&&%':

13t(De)e$#e* +014


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CONTENT PAGE

1.0 INTRODUCTION TO HEAT EXCHANGER 3

2.0 GOVERNING EQUATION 4

3.0 SIMULATION METHOD 5

4.0 RESULTS AND DISCUSSION

5.0 CONCLUSION

6.0 REFERENCES


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1.0 Introduction to Heat Exchanger

The general function of a heat exchanger is to transfer heat from one uid toanother. The basic component of a heat exchanger can be viewed as a tube withone uid running through it and another uid owing by on the outside. There arethus three heat transfer operations that need to be described:

1. Convective heat transfer from uid to the inner wall of the tube2. Conductive heat transfer through the tube wall, and. Convective heat transfer from the outer tube wall to the outside uid.

!eat exchangers are typically classi"ed according to ow arrangement and type ofconstruction. The simplest heat exchanger is one for which the hot and cold uidsmove in the same or opposite directions in a concentric tube #or double$pipe%construction. &n the parallel$ow arrangement of 'igure 1 , the hot and cold uidsenter at the same end, ow in the same direction, and leave at the same end. &n thecounterow arrangement of 'igure 2, the uids enter at opposite ends, ow inopposite directions, and leave at opposite ends.

]

1.1 Internals of Shell and Tube Heat Exchanger

'igure 2: Counter'igure 1: (arallel


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)

'igure 1: *hell and tube exchangerThe shell and tube exchanger consists of four ma+or parts:

'ront !eaderThis is where the uid enters the tubeside of the exchanger. &t is sometimesreferred to as the *tationary !eader.

ear !eaderThis is where the tubeside uid leaves the exchanger or where it is returnedto the front header in exchangers with multiple tubeside passes.

Tube bundleThis comprises of the tubes, tube sheets, ba-es and tie rods etc. to hold thebundle together.

*hellThis contains the tube bundle.

2.0 Governing Equations

The multi$uid model section describes the general formulation of the modeleuations. The homogeneous model explained in the next section is a simpli"cationto this general formulation. The multi uid model will be used to setup /uler$/ulersimulations, whereas the homogeneous model will be used to implement 0'

simulations.2.1 Multi!luid Model

The general scalar advection$diusion euation:

'or momentum euations this ta3es the form:

The continuity euation:

and


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The formulas above de"ne 4 5p61 euations for the following 75p un3nowns:

'or this system of euations to be solved, 75p$1 more euations need to be added.&n this research, the additional euation de"nes that all phases share the samepressure "eld:

8ny additional uantities to be solved, such as tracer concentrations, ta3e thegeneral form of the advection diusion euation, without interface transfer terms.

2.2 Ho"ogeneous Model&n the homogeneous model, all transported uantities, but volume fraction areta3en to be eual for all phases. Therefore, the general advection diusion euationfor a given uantity can be summed over all phases to give:

9ith:

#

#and

5ow the advection diusion euation does no longer show interphase transferterms. The momentum euations simplify to

with

8n assumption in the euations above is that the velocity "eld is shared between allphases, i.e. no slip is present between the phases. This assumption is valid if thegrid on which the euations are being solved is "ne enough to ensure a single cellmainly contains one of the phases. The velocity at this position will identify thevelocity of the phase present at this position.

2.$ Turbulence Models


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&n this research the general single phase model, extended for the use in multi$phasesystems, has been used. &n this model, the eective viscosity in the momentumeuations is the sum of the molecular and a turbulent viscosity:

with

!ere, 3 represents the 3inetic energy and represent the rate of turbulencedissipation. The volume fraction euation is modi"ed in the following way:

with:

The transport euations for 3 and :

with

in which shear production ( and production due to body forces for incompressibleows are given by:

The model has the following model parameters: . &n addition,the (randtlnumbers for the various uantities need to be speci"ed.

2.% Inter&hase Trans&ort Ter"s&n this research, transport between the phases is only ta3en into account formomentum.


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*ince there is no ow through the wall, there is no need to specify a boundarycondition for volume fractions at walls.@any variables will show sharp gradients near the walls. To prevent having to use avery "ne grid near the wall to handle these sharp gradients, wall functions are beingused to solve the pro"les near the wall.'or turbulent 3inetic energy 3 the wall shear stress in a small boundary layer with

thic3ness d is ta3en to be

5ear the wall, two scaled variables are de"ned: a scaled velocity componentparallel to the wall:

and a scaled distance to the wall:

The scaled velocity component is calculated from:

with being eual to the upper root of:

!ere, and / are model parameters de"ning the thic3ness and steepness of the

logarithmic boundary layer.

$.0 Si"ulation Method

Model /iard&n the *pace, ;imension, 2; axisymmetric coordinate system was selected in thegiven geometry. 5ext button was clic3ed to proceed with the next step.&n the 8dd (hysics, 5on$&sothermal ABaminar 'low was chosen. (lus button wasclic3ed to add followed by the next button.&n the *elect *tudy Type, stationary study was clic3ed, followed by the "nish button.

Geo"etr-

,uild rectangle&n @odel


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,oolean &eration 'ierence1% ?nder @odel


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5elocit- 6eld strea"line in 2'

eometry eometr

!emala1FEK4

Lara 1F7FME.1K

M E.22L E.1

M E.1K

L


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8s illustrated in the "gures above, 'igure 8 and < describe the dierences in the

water velocity ow. &n 'igure 8, due to a longer length in the L dimension, the

presence of dead >ones, also 3nown as the stagnation areas, are much lesser

compared to 'igure ones. n the other hand, in "gure


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The temperature pro"le in the heat exchanger exhibits almost similar pattern in

both "gures as shown above. &n both "gures, the dar3 red region around the inlet

area indicates the water entrance to the heat exchanger at a lower temperature,

thus proceeds to the outlet stream of the respective heat exchanger. 8s it ows

towards the outlet stream, the water is heated up to raise up the temperature in

order to study the heat transfer performance. This reason is clearly evident as the

bright red colour observed throughout towards the outlet of the heat exchanger

indicates the increase in the water temperature pro"le. 5evertheless, the variances

in the dimensions of x and y for both the "gures above distinguishes the distribution

of the heat ux along the heat exchanger. Boo3ing at the middle section of the

exchanger in 'igure ;, the bright red region gives an indication that more heat are

being transferred from the coil compared to 'igure C. !owever, due to the shorter

length in L dimension of 'igure ;, less heated water is being transferred to the

outlet stream. &n short, less heat is observed in the outlet stream of the heat

exchanger.

M E.22

L E.1

M E.1K

L


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Te"&erature $'


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M E.22

L E.1

M E.1K

L

M E.22

L E.1

M E.1K

L


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&n both &so$surface designs obtained, the distribution of the heat ux generated

from the inlet up to the outlet stream is almost similar which is illustrated by the

decreasing intensity of the blue colour. The main emphasis here, however, is by

observing at the middle section of heat exchanger again. The distribution of the

heat ux in the middle section of "gure ' pro+ected to be longer and more

concentrated towards the output no>>le. 'or "gures and !, the description of the

contour pattern obtained is similar for both dierent dimensions as shown in the

"gures above. &n short, more heat is being distributed in "gure as compared to

the next "gure

5elocit- $'

M E.22

L E.1

M E.1K

L


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Heat 5ie8 fro" the To& *art of the Heat Exchanger 7 9ine gra&h

The image above displays the outlet surface temperature of both heat exchangers.The centre portion of this contour plot represents the outlet of the heat exchangerfrom the top view. This is the portion where the water heated by the coil of the heatexchanger passes through. &t is clearly seen that the centre portion is red in colour

which indicates that the temperature is high since this portion is closer to theheating coil. &t is also observed that the the contour changes from yellow, green and"nally blue as it approaches the wall because heat tends to escape to surroundingat the surface of the heat exchanger.


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14E 17E 1FE 1HE 1KE 1IE 2EE 21E 22EEE

E1

E2

E

E4

E7

EF

EH

ME.22 LE.1

1KE 2EE 22E 24E 2FE 2KE EE 2EE2

E

E4

E7

EF

EH

EK

EI

1E

11

12

ME.1K LE.1F

The values were plotted according to the axis and were analy>edbetween both heat exchangers with dierent M and Ldimensions. 8s portrayed in the graph, the heat transfercoe=cient is directly proportional to the average outlet, T2,which shows that the higher value of heat transfer coe=cient,

the greater the outlet temperature that we will obtain.Th h!"

"#!$% '(&&)')$" )% )$&*+$', - "h "h)'/$%% !$, "h#!*

'($,+'"))" (& "h ,)+% "h#(+h h)'h h!" )% "#!$%#,. Th *!##

"h h!" "#!$% '(&&)')$" "h !%)# h!" )% "#!$%#,.


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Trial and error &rocess to deter"ine heat transfer

coe4cient

14E 17E 1FE 1HE 1KE 1IE 2EE 21E 22EE

E.7

1

1.7

2

2.7

.7

4

ME.22 LE.1

1KE 2EE 22E 24E 2FE 2KE EE 2EE

2

4

F

K

1E

12

ME.1K LE.1F

'rom the trial and error, we obtained the suitable heat transfercoe=cient that is reuired to operate both the heat exchangerwith its respective dimensions as displayed in the graph . 'or thedimension #ME.1K,LE.1F%, the optimum heat transfercoe=cient is found to be 211 9J#m2G% for the heat exchanger to


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operate whereas for the dimension #ME.22,LE.1% , theoptimum heat transfer coe=cient is found to be 2EK 9J#m2G%.

Th !*+ (& h!" "#!$% '(&&)')$" )% ,)&$" -'!+% "h !$, !#

,)&$" )$ -("h '!%%.H!" "#!$% '(&&)')$" !$, "h "#!"+#

,)%"#)-+")($ !# #!"* !&&'", - "h ,)&$' (& "h (%)")($ (& "h

')#'*% !$, "h #'"!$*. Th h!" "#!$% '(&&)')$" )% )$&*+$', - "h

"h)'/$%% !$, "h#!* '($,+'"))" (& "h ,)+% "h#(+h h)'h h!" )%

"#!$%#,. A *!# h!" "#!$% '(&&)')$" !**(% h!" "( - "#!$%#,

!%)* )$ "h h!" 'h!$#. 7!%, ($ (+# #%+*" h!" )% !%)# )$ "h &)#%"

h!" 'h!$# h)'h h(*,% ! h)h# !*+ (& h!" "#!$% '(&&)')$".

+.0 :9;SI:

I$ '($'*+%)($ "h h!" "#!$% '(&&)')$" &(# -("h !#" )% ,)&$".Th h!" "#!$% '(&&)')$" (& "h &)#%" h!" 'h!$#8G("# 19 )%

%*)h"* h)h# h)'h )% 211 :;2.< !% '(!#, "( "h %'($, h!"

'h!$# 8G("# 29 h)'h )% 20= :;2.< . Th)% %h(% "h!" h!" )%

"#!$%#, !%)* )$ "h "h &)#%" h!" 'h!$#


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6.0 References

7!#"*"" D. 820139. Th F+$,!$"!*% (& H!" E'h!$#%. Th I$,+%"#)!*

Ph%)')%". R"#), ( h"">;;.!).(#;");INPHFA;(*?2;)%%?4;1=.,&

Th#(,)!. 820129 Sh** A$, T+- H!" E'h!$#%. A?"(?@ G+), "(

Th#(,$!)'% H!" M!%% T#!$% !$, F*+), E$)$#)$. R"#), (

h"">;;."h#(,)!.'(;

T(h*)$ B. E. 81=9. P#)$')!* G(#$)$ E+!")($%. The Structure, Stability,

and Dynamics of Self-Gravitating Systems. R"#), (

h"">;;.h%.*%+.,+;!%"#(;H7((/.'+##$";C($"";PGE;PGE.h"*
http://www.aip.org/tip/INPHFA/vol-2/iss-4/p18.pdfhttp://www.phys.lsu.edu/astro/H_Book.current/Context/PGE/PGE.htmlhttp://www.phys.lsu.edu/astro/H_Book.current/Context/PGE/PGE.htmlhttp://www.aip.org/tip/INPHFA/vol-2/iss-4/p18.pdf

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