numerical simulation of forced convection heat transfer enhancement by porous pin fins in...

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),

ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 51-64 © IAEME

51

NUMERICAL SIMULATION OF FORCED CONVECTION HEAT TRANSFER

ENHANCEMENT BY POROUS PIN FINS IN RECTANGULAR CHANNELS

Manjunatha Reddy1, Dr. G S. Shivanshankar M.E.,Ph.D

1(M.Tech Student, Dept of Mechanical Engg, Siddaganga Institute of Technology, Tumkur)

2(Professor and Head, Dept of Mechanical Engg, Siddaganga Institute of Technology, Tumkur)

ABSTRACT

Pin fins have a variety of applications in industry due to their excellent heat transfer

performance, e.g., in cooling of electronic components, in cooling of gas turbine blades, and

recently, in hot water boilers of central heating systems. The forced convective heat transfer in three-

dimensional porous pin fin channels is numerically studied using ANSYS Fluent. Geometric

modelling is done using Design Modeller and CFD Meshing is carried out using ANSYS Meshing

Preprocessor. The effects of Reynolds number (Re), pore density (PPI) and pin fin form are studied

in detail.

The results show that, with proper selection of physical parameters, significant heat transfer

enhancements and pressure drop reductions can be achieved simultaneously with porous pin fins and

the overall heat transfer performances in porous pin fin channels are much better than those in

traditional solid pin fin channels. The effects of pore density are significant. As PPI increases, the

pressure drops and heat fluxes in porous pin fin channels increase while the overall heat transfer

efficiencies decrease and the maximal overall heat transfer efficiencies are obtained at PPI 20.

Furthermore, the effects of pin fin form are also remarkable. With the same physical parameters, the

overall heat transfer efficiencies in the long elliptic porous pin fin channels are the highest while they

are the lowest in the short elliptic porous pin fin channels.

Keywords: CFD, Heat Transfer, Pin Fin, Porous.

I. INTRODUCTION

Forced convection heat transfer in a channel or duct fully or partially packed with porous

material is of considerable technological interest. This is due to the wide range of applications such

as direct contact heat exchangers, electronic cooling, heat pipe etc. It has been demonstrated that

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING

AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)

ISSN 0976 – 6359 (Online)

Volume 5, Issue 7, July (2014), pp. 51-64

© IAEME: www.iaeme.com/IJMET.asp

Journal Impact Factor (2014): 7.5377 (Calculated by GISI)

www.jifactor.com

IJMET

© I A E M E



52

insertion of a high-conductivity porous material in a cooling passage can have a positive effect on

convective cooling. An important class of problems directly related to porous matrix convection is

heat and fluid flow in composite systems, that is, systems consisting partly of a fluid-saturated

porous material and partly of a fluid. The convection phenomenon in these systems is usually

affected by the interaction of the temperature and flow fields in the porous spaces and the open

spaces. The importance of this class of problem is justified both in a fundamental and in a practical

sense. With reference to practical thermal engineering applications which stand to benefit if a better

understanding of heat and fluid flow processes in composite systems is acquired, the following

examples are cited: fibrous and granular insulation which occupies only part of the space between a

hot and a cold boundary, fault zones in geothermal systems, the cooling of stored grain, and heat

removal from nuclear debris beds in nuclear reactor safety.

The major challenges to the design of a heat exchanger are to make it compact, i.e., to

achieve a high heat transfer rate and, at the same time, to allow its operation with a small power loss.

These aims of research and development have not changed over the years but, most recently, high

energy and material costs have resulted in increased efforts to design and produce more and more

efficient heat exchanger equipment.

Fig.1: Pin-Fin Heat sink



53

N. Sahiti et al.[1] demonstrated a considerable heat transfer enhancement by using small

cylindrical pins on surfaces of heat exchangers. It uses simple relationships for the conductive and

convective heat transfer to derive an equation that shows which parameters permit the achievement

of heat transfer enhancements.

N. Sahiti et al.[2] shown that the selection of elements for heat transfer enhancement in heat

exchangers requires a methodology to make a direct comparison of the performances of heat

exchanger surfaces with different elements.

Pei-Xue Jiang et al.[3] Experimentally investigated forced convection heat transfer of water and air

in sintered porous plate channels. The effects of fluid velocity, particle diameter, type of porous

media (sintered or non-sintered), and fluid properties on the convection heat transfer and heat

transfer enhancement were investigated.

Y. Wang and K. Vafai [4] conducted an experimental investigation of the convective heat

transfer and pressure loss in a rectangular channel with discrete flush-mounted and protru ding heat

sources. Six protruding obstacle heights, which represent the range of the dimensionless protrusion

of 0≤ h /H ≤ 0.805, are studied

Hyung Jin Sung et al.[5] did a numerical study of flow and heat transfer characteristics of forced

convection in a channel that is partially filled with a porous medium. The flow geometry models

convective cooling process in a printed circuit board system with a porous insert. The channel walls

are assumed to be adiabatic.

F. Benkafada et al.[6] carried a two dimensional numerical simulation of the laminar air

forced convection cooling of six blocks mounted on the lower wall of a plane horizontal channel

filled (or not filled) with a porous medium. Mounted in the channel filled with the porous matter.

Thus, the use of porous media when possible is recommended because it enhances the cooling of

heated blocks mounted in channels.

Habibollah sayehvand And Hossein Shokouhmand [7] did a numerical study of laminar fully

developed forced convection in a pipe partially filled with a porous medium.

Hadi Dehghan et al.[8] conducted a detailed numerical investigation of two-dimensional laminar

forced convection in a porous channel with inlet and outlet slot. A uniform heat flux is applied on

one wall of channel and an-other wall is isolated.

P.C.Huang, K.Vafai [9] presented a detailed investigation of forced convection enhancement

in a channel using multiple emplaced porous blocks. The brinkman-Forchheimer extended Darcy

model is used to characterize the flow field inside the porous regions in order to account for the

inertia effects as well as the viscous effects.

M.R.Asif et al. [10] carried out to investigate the mixed convective two dimensional flows in

a vertical enclosure with heated baffles on side walls. All walls are assumed to be adiabatic, but

baffles are considered as isothermally heated.

Somchai Sripattanapipat A et al.[11] Investigated Laminar periodic flow and heat transfer in

a two dimensional horizontal channel with isothermal walls and with staggered diamond-shaped

baffles numerically. The computations are based on the Finite volume method and the SIMPLE

algorithm has been implemented.

II. MATHEMATICAL MODELS OF FLUENT

All the fluids investigated in this research are Newtonian. This means that there exists a linear

relationship between the shear stress, σij , and the rate of shear (the velocity gradient). In CFX, this

is expressed as follows:

�� ……………… . .1



54

In FLUENT, these laws are expressed in the following form:

Law of Conservation of Mass: Fluid mass is always conserved.

��

�� …………… . . . �

Newton’s 2

nd Law: The sum of the forces on a fluid particle is equal to the rate of change of

momentum.

��

��

�� !��

��" � #�…………… . . . $

First Law of Thermodynamics: The rate of head added to a system plus the rate of work done on a

fluid particle equals the total rate of change in energy.

�� %&� �

�� %&� �

�� '

�(��

�� …………… . . . )

The fluid behaviour can be characterised in terms of the fluid properties velocity vector u

(with components u, v, and w in the x, y, and z directions), pressure p, density ρ, viscosity µ, thermal

conductivity λ, and temperature T. The changes in these fluid properties can occur over space and

time. H is the total enthalpy, given in terms of the static (thermodynamic) enthalpy, h:

After going through literature review certain gap findings have been determined. In the work

of Yang et al. [12] only air and water are investigated and the performances of other fluids are still

unknown. The performance of nano fluid in porous medium can have positive effect on heat transfer

augmentation is the important gap found during the literature review. The discrete heating of the

rectangular channel partially filled with porous medium is of considerable technological interest.

Removing the adiabatic walls of rectangular channel and maintaining them at constant temperature,

varying the cross sectional area of porous pin fin over the base wall area in single pin fin array unit

cell, changing the material properties of porous pin fin are some of the other gap findings that has

been determined.

III. GEOMETRIC MODEL

As shown in 2 the physical model is derived from traditional pin fin heat sink, which

generally consists of a bottom wall, two side walls, a top wall, and a pin fin array. The bottom wall is

hot and its temperature is kept at Th. The side and the top walls are kept adiabatic. The pin fin array

is made of high porosity metal foams aluminum and arranged in stagger; air and water are used as

the cold fluids. In order to obtain a basic understanding of flow and heat transfer performances in

porous pin fin heat exchangers, a simplified porous pin fin channel with appropriate boundary

conditions is adopted for the computations, which can be regarded as forced convection heat transfer

in a partially filled porous channel The computational domain is depicted in Fig. 4.1 b and 4.2 which

is composed of a developing inlet block L1=10 mm, two pin fin array unit cells L2=2×6.52 mm, and

a developing outlet block L3=70 mm.



55

The dimensions of the computational domain are Length (L) 93.04 mm, Width (W) 3.26 mm,

Height (H) 10 mm. The total area of pin fin cross-sections over the base wall area in single pin in

array unit cell is 15%, which is reasonable for industry applications.

Fig.2: Physical model: a) porous pin fin heat sink and

b) representative computational domain

Fig.3: Porous pin fin cross-section Circular form



56

Fig.4. Porous pin fin cross-section long elliptic form

Fig.5: Porous pin fin cross-section short elliptic form

IV. CFD MESHING AND BOUNDARY CONDITIONS

CFD meshing is done by using ANSYS Meshing software. Total no of elements used in this

simulation is approximately for all cases is 35000.



57

Fig.6: CFD Meshing of Pin-fin

Fig.7: Boundary conditions

The temperature and velocity of inlet are kept at Tin and uin, respectively. The bottom wall

of pin fin array unit cells is the hot wall and the temperature is kept at Th. Two other bottom walls

and all top walls are kept adiabatic. The symmetry boundary conditions are adopted for two side

walls and the flow and heat transfer of outlet are considered to be fully developed. Furthermore,

three different kinds of porous pin fins with circular, long elliptic, and short elliptic cross-section

forms are employed to investigate the pin fin configuration effects and the cross-section areas of

different pin fins are identical with each other Apin =3.14 mm2. The physical dimensions and cross-

section forms of different porous pin fins are presented in Fig. 4.3, 4.4 and 4.5.



58

Parameters studied in project

In this Project Air is employed as the cold fluids and the effects of Reynolds number (Re),

pore density (PPI) and pin fin form are studied.

Table 1: Parameters studied for the simulation

Solid Pin fin Pin fin-PPI 30 Pin fin-PPI 40

Fin Type Inlet Velocity

m/s

Inlet Velocity

m/s

Inlet Velocity

m/s

Circular 0.5 0.5 0.5

1 1 1

1.5 1.5 1.5

2 2 2

Long

Elliptical

0.5 0.5 0.5

1 1 1

1.5 1.5 1.5

2 2 2

Short

Elliptical

0.5 0.5 0.5

1 1 1

1.5 1.5 1.5

2 2 2

V. RESULTS AND DISCUSSIONS

The pressure distributions in solid pin fin channels are shown in Fig. 8. It shows the Pressure

drop of 0.7 Pa fro inlet velocity of 0.5 m/s. The temperature distributions in solid pin fin channels are

shown in Fig. 9. It shows that the internal temperatures of solid pin fins are quite uniform and the

average temperatures are high, which are 342.2 K. The temperature rise in the channel inlet to outlet

is 21.3K. The velocity vector distributions in solid pin fin channels are presented in Fig. 4.10. It

shows that large vortices are formed behind solid pin fins. In solid pin fin channels, the solid pin fins

are totally impermeable. Similar Trend is shown in 4.13.

Table 2: Comparison of Pressure drop and Temperature rise in Circular Pin-Fin

Fin Type Inlet

Velocity

m/s

Temperature

Rise K

Pressure

Drop Pa

Circular 0.5 21.3288 0.709819

1 14.92 2.35157

1.5 12.4976 4.9089

2 11.0747 8.32347



59

A. Circular Results

Fig.8: Pressure contours solid and circular pin fin channels-Inlet velocity 0.5m/s

Fig.9: Temperature contours solid and circular pin fin channels- Inlet velocity 0.5m/s



60

Fig.10: Velocity contours solid and circular pin fin channels- Inlet velocity 0.5m/s

The flow and heat transfer performances in circular porous pin fin channels are carried out.

The circular porous pin fin form see Fig. 5.1 is selected for present study. Air Pr=0.7 are used as cold

fluids and the Reynolds number Re varies from 1000 to 2291 with φ=0.9 PPI =30. Tin=293 K, and

Th=343 K.

The pressure distributions in Porous circular pin fin channels are shown in Fig. 11. It shows

the Pressure drop of 0.67 Pa for inlet velocity of 0.5 m/s. It shows the lower pressure drop compared

to circular solid channel due to Porosity in the solid region. The temperature distributions in circular

porous pin fin channels are shown in Fig. 12. The internal temperatures of porous pin fins are not so

uniform and the average temperatures are much lower, which are 330 K. Also, the fluid temperatures

in porous pin fin channels are higher than those in solid pin fin channels. The average exit

temperature rise in porous pin fin channels is 26.64 K. However in the solid circular pin fin the

internal temperatures of solid pin fins are quite uniform and the average temperatures are high, which

are 343K. Also the solid the temperature rise in the channel inlet to outlet is 21K. These results

indicate that more heats can be transported away by using porous pin fins and their heat transfer

performances would be better. This is because the porous pin fins can greatly enlarge the contact

surface areas and mix the fluid flow inside, which may lead to significant heat transfer

enhancements.

Table 3: Comparison of Pressure drop and Temperature rise in Circular pin-fin(PPI=30)

Fin Type Inlet

Velocity

m/s

Temperature

Rise K

Pressure

Drop Pa

Circular 0.5 26.6488 0.6774

1 21.6226 1.95834

1.5 18.7446 3.44732

2 16.7798 5.07131



61

B. Porous (PPI=30) Circular Pin-Fin results

Fig.11: Pressure contours porous (PPI=30) circular pin fin channels-Inlet velocity 0.5m/s

The velocity vector distributions in solid pin fin channels are presented in Fig. 13. It shows

that with the same Reynolds number, the fluid velocities in solid pin fin channels are much higher

than those in porous pin fin channels. Large vortices are formed behind solid pin fins while no such

vortices are found in porous pin fin channels. In solid pin fin channels, the solid pin fins are totally

impermeable and this would narrow the flow passages and enhance the flow tortuosities inside.

While in porous pin fin channels, the porous pin fins are permeable and the fluid can flow through

them directly. This would widen the flow passages and lower the flow tortuosities inside. Therefore,

the flow resistances and pressure drops in porous pin fin channels would be lower. Similar Trend is

shown in Fig.5.6 for inlet velocity of 1 m/s.

Fig.12: Temperature contours porous (PPI=30) circular pin fin channels- Inlet velocity 0.5m/s



62

Fig.13: Velocity contours porous (PPI=30) circular pin fin channels- Inlet velocity 0.5m/s

Table 4: Comparison of Pressure drop and Temperature rise in Circular, Long Elliptical and

short Elliptical (PPI=30)

Fin Type Inlet

Velocity

m/s

Temperature

Rise K

Pressure

Drop Pa

Circular 0.5 26.6488 0.6774

1 21.6226 1.95834

1.5 18.7446 3.44732

2 16.7798 5.07131

Long

Elliptical

0.5 21.2587 0.362434

1 16.0238 1.10911

1.5 13.6143 2.0637

2 12.2815 3.17423

Short

Elliptical

0.5 32.7796 1.15565

1 27.4522 2.8647

1.5 23.5242 4.64382

2 20.6503 6.46394

The velocity vector distributions in solid pin fin channels are presented in Fig. 5.15.It shows

that with the same Reynolds number, the fluid velocities in solid pin fin channels are much higher

than those in porous pin fin channels. Large vortices are formed behind solid pin fins while no such



63

vortices are found in porous pin fin channels. In solid pin fin channels, the solid pin fins are totally

impermeable and this would narrow the flow passages and enhance the flow tortuosities inside.

While in porous pin fin channels, the porous pin fins are permeable and the fluid can flow through

them directly. This would widen the flow passages and lower the flow tortuosities inside. Therefore,

the flow resistances and pressure drops in porous pin fin channels would be lower. Similar Trend is

shown in Fig.5.18 for inlet velocity of 1 m/s.

VI. CONCLUSION

The forced convective heat transfer in three-dimensional porous pin fin channels is

numerically studied in this paper. Air is used as the cold fluids and the effects of Reynolds number,

pore density, and pin fin form are performed using ANSYS CFD Fluent software. Geometric

modeling is carried out using ANSYS Design Modeler and CFD meshing is done by ANSYS

meshing platform.

The flow and heat transfer performances in porous pin fin channels are also compared with

those in traditional solid pin fin channels in detail. The major observations are as follows.

• With proper selection of metal foams, such as PPI=30, significant heat transfer enhancements

and pressure drop reductions can be achieved simultaneously by using porous pin fins and the

overall heat transfer efficiencies in porous pin fin channels are much higher than those in

solid pin fin channels, which are 50%.

• The effects of pin fin form are also remarkable. With same physical parameters, the pressure

drops and heat fluxes are the highest in short elliptic porous pin fin channels and lowest in

long elliptic porous pin fin channels.

• With the same physical parameters, the overall heat transfer efficiencies in the long elliptic

porous pin fin channels are the highest while they are the lowest in the short elliptic porous

pin fin channels.

REFERENCES

[1]. Pelaez, R.B., Ortega, J.C., Cejudo-Lopez, J.M., A three-dimensional numerical study and

comparison between the air side model and the air/water side model of a plain fin and tube

heat exchanger, Applied Thermal Engineering, 30 (2010), pp.1608-1615.

[2]. Sahin, H.M., Dal, A.R., Baysal, E., 3-D Numerical study on correlation between variable

inclined fin angles and thermal behavior in plate fin-tube heat exchanger, Applied Thermal

Engineering, 27 (2007), pp.1806-1816.

[3]. Wen, M.Y. Ho, C.Y., Heat transfer enhancement in fin and tube heat exchanger with

improved fin design, Applied Thermal Engineering, 29(2009), pp.1050-1057.

[4]. Yan, W.M., Sheen, P.J., Heat transfer and friction characteristics of fin and tube heat

exchangers, International Journal of Heat and Mass Transfer, 43 (2000), pp.1651-1659.

[5]. Wolf, I., Frankovic, B., Vilicic, I., A numerical and experimental analysis of neat transfer in

a wavy fin and tube heat exchanger, Energy and the Environment (2006) pp.91-101.

[6]. Tang, L.H., Zeng, M., Wang, Q.W., Experimental and numerical investigation on air side

performance of fin and tube heat exchangers with various fin patterns, Experimental

Thermal and Fluid science, 33(2009), pp.818-827.

[7]. Wang, C.C., Lo, J, Lin, Y.T. Wei, C.S., Flow visualization of annular and delta winlet

vortex generators in fin and tube heat exchanger application, International Journal of Heat

and Mass Transfer, 45, (2002), pp.3803-3815.



64

[8]. Fiebig, M., Valencia, A., Mitra, N.K.., Local heat transfer and flow losses in fin and tube

heat exchangers with vortex generators: A comparison of round and flat tubes, Experimental

Thermal and Fluid Science, 8(1994), pp.35-45.

[9]. Leu, J.S., Wu, Y.H., Jang, J.Y., Heat transfer and fluid flow analysis in plate-fin and tube

heat exchangers with a pair of block shape vortex generators, International Journal of Heat

and Mass Transfer, 47 (2004), pp. 4327-4338.

[10]. Leu, J.S., Liu, M.S., A numerical investigation of louvered fin and tube heat exchangers

having circular and oval tube configurations, International Journal of Heat and Mass

Transfer, 44 (2001), pp. 4235-4243.

[11]. Joen, C.T et al., Interaction between mean flow and thermo-hydraulic behaviour in inclined

louver fins, International Journal of Heat and Mass Transfer, 54, (2011), pp.826-837.

[12]. Zhang, X., Tafti, D.K., Flow efficiency in multi-louvered fins, International Journal of Heat

and Mass Transfer, 46, (2003), pp.1737-1750.

[13]. Li, W., Wang, X., Heat transfer and pressure drop correlations for compact heat exchangers

with multi-region louver fins, International Journal of Heat and Mass Transfer, 53 (2010),

pp.2955-2962.

[14]. Wang, C.C., Lee, C.J., Chang, C.T., Lin, S.P., Heat transfer and friction correlation for

compact louvered fin and tube heat exchangers, International Journal of Heat and Mass

Transfer, 42 (1999), pp.1945-1956.

[15]. T.A. Cowell and A. Achaichia, “Heat Transfer and Pressure Drop Characteristics of Flat

Tube and Louver Plate FinSurfaces”, Experimental Thermal and Fluid Science, No.1, 1988,

p147-157.

[16]. Chang, Y.J., Wang, C.C., A generalized heat transfer coefficient for louver fin geometry,

International Journal of Heat and Mass Transfer, 40, (1997), pp.533-544.

[17]. Omar Mohammed Ismael, Dr. Ajeet Kumar Rai, Hasanfalah Mahdi and Vivek Sachan, “An

Experimental Study of Heat Transfer In A Plate Heat Exchanger”, International Journal of

Advanced Research in Engineering & Technology (IJARET), Volume 5, Issue 4, 2014,

pp. 31 - 37, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

[18]. Sunil Jamra, Pravin Kumar Singh and Pankaj Dubey, “Experimental Analysis of Heat

Transfer Enhancement in Circular Double Tube Heat Exchanger Using Inserts”,

International Journal of Mechanical Engineering & Technology (IJMET), Volume 3,

Issue 3, 2012, pp. 306 - 314, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.

[19]. S. Bhanuteja and D.Azad, “Thermal Performance and Flow Analysis of Nanofluids In A

Shell and Tube Heat Exchanger”, International Journal of Mechanical Engineering &

Technology (IJMET), Volume 4, Issue 5, 2013, pp. 164 - 172, ISSN Print: 0976 – 6340,

ISSN Online: 0976 – 6359.

[20]. N.G.Narve and N.K.Sane, “Heat Transfer and Fluid Flow Characteristics of Vertical

Symmetrical Triangular Fin Arrays”, International Journal of Advanced Research in

Engineering & Technology (IJARET), Volume 4, Issue 2, 2013, pp. 271 - 281, ISSN Print:

0976-6480, ISSN Online: 0976-6499.