Cfd and conjugate heat transfer analysis of heat sinks with different fin geometries subjected to foced convection used in electronics cooling

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
_______________________________________________________________________________________
Volume: 04 Issue: 06 | June-2015, Available @ http://www.ijret.org 158
CFD AND CONJUGATE HEAT TRANSFER ANALYSIS OF HEAT
SINKS WITH DIFFERENT FIN GEOMETRIES SUBJECTED TO
FOCED CONVECTION USED IN ELECTRONICS COOLING
V. M Kulkarni1
, Basavaraj Dotihal2
1
Professor, Thermal Power Engineering, VTU RC Gulbarga, karnataka, India
2
Student, Thermal Power Engineering, VTU RC Gulbarga, karnataka, India
Abstract
Heat sinks are commonly used for cooling of electronic devices. Heat sinks, an array of heat fins, remove the heat from the
surfaces of the chips by enhancing the heat Transfer rate through heat conduction process. Heat can also be removed from the
chip surfaces through forced convection heat transfer. In this project work, CFD and conjugate heat transfer analysis is carried
out for various fin geometries with Zigzag, Fluted, Slanted mirror, Custom pin fin and staggered array configurations for low
thermal resistance and minimum pressure drop. Numerical simulations are carried out for each of the above mentioned fin
geometries with common base plate thickness of 2 mm, fin height of 28 mm and fin thickness of 1 mm for three different heat loads
namely 50 W, 75 W and 100 W with air flow of 3.933 m/s (15 ft3/min or 15 CFM) and air inlet temperature of 25o
C. The results
are compared for thermal performance of a heat sink for each of above geometries and it is observe that the fin with Slanted
Mirror geometry gives the best performance among all the other geometries for minimum Pressure drop. The average heat
transfer coefficients for fins with slanted mirror geometry, zig zag configuration, fluted type, custom pin fin and staggered array
are found to be 215 W/m2K, 164 W/m2K, 164 W/m2K, 157 W/m2K and 145 W/m2K respectively
Keywords: Fin geometries of Heat sinks, Computational Fluid Dynamics, Conjugate heat transfer.
--------------------------------------------------------------------***----------------------------------------------------------------------
1. INTRODUCTION
Nowadays trend in electronics industry to produce small and
compact size goods that can be accommodated in given
space, which is constraint in many cases. The heat generated
due to active components in such electronic devices is
enormous, may be the order of 100 W/m2
. It is therefore
necessary to remove the heat generated, which otherwise
detriment to the life of such devices and their reliability.
Heat sinks are used to remove the heat generated in
electronic components. Heat sink is nothing but an array of
fins or extruded surfaces remove the heat from the localized
point through heat conduction and convective heat transfer
process. Heat sink is attached to a electronic chip to help
prevent the chip from overheating. In order to design a
better heat sink, factors are such as higher heat transfer rate,
low pressure drop, lowest maximum temperature attained in
operation, lower thermal resistance, easy manufacturing
process, a simple structure and material with high thermal
conductivities are to be considered.
1.1 Objectives
The main objective of the work is presented as
1. To investigate the conjugate heat transfer analysis for
heat sinks those are being used in electronics cooling.
This involves the combined fluid flow analysis by
making use of CFD equations and heat transfer
analysis, considering separately convection process in
fluid flow region and conduction heat transfer in solid
region.
2. To carry out heat transfer analysis for different fin
configurations considering the conduction heat transfer
from base plate to heat fins.
3. To conduct computational fluid flow analysis for
different fin configurations, for fluid part, by solving
Navier-Stroke equations to get velocity vectors,
pressure contours and temperature fields for given inlet
air velocity. Standard k- ε model is adopted to account
for turbulence phenomenon. The temperature field is
used to get quantity of heat dissipated or carried away
by convection.
4. To determine the heat transfer coefficient, Nusselt no,
Thermal resistance and Pressure drop through
numerical to predict the thermal performance of a fin
for different geometrical configuration.
5. .To select best heat sink with suitable fin geometry for
lower thermal resistance, higher heat transfer
coefficient and with minimum resistance
1.2 Fin Geometries of Heat Sink
Geometries of fins in heat sinks are showed in below figure
1
a) Zigzag array.
b) Fluted array.
c) Slanted mirror array.
d) Custom pin fin array.
e) Staggered array.

_______________________________________________________________________________________
These are five different fin geometries are considered for
fluid flow and heat transfer analysis.
Fig. a Fig. b
Fig. c Fig. d
Fig. e
Fig 1 Different Fin Geometries of Heat sinks
2. LITERATURE REVIEW
The thermal network of a finned heat sink consists of
conductive, radiative, and convective resistances. From the
junction of the device, heat is transported by conduction
from the device through the interface and into the heat sink
from which heat is usually removed by means of convection
and radiation cooling to minimize any significant
conduction resistance though the fins and improve the
overall performance of the heat sink. There exists significant
work carried out in the thermal analysis of heat sink
design.C.L Chapman et al [1] are analyzed the detailed
comparison of thermal performances of different fin
geometries by experimentally and theoretically. In this they
investigated cross cut pin fin, straight or parallel plate fins
and they compare with elliptical pin fins in their work. And
they conclude Extruded straight design performed
significantly better than either of the other two designs over
the flow range examined. Denpange Soodphadkee et al [2]
analyzed the performances of Round, Elliptical and Plate
fins Staggered and in-line configuration. In this they
compare different fin geometries and they were simplifying
by assuming periodically developed 2D flow and isothermal
heat transfer surface. In general it is found that rounded
geometries outperform similarly sharp edged fin shapes. By
comparing all finally they concluded staggered shows better
performance than in-line. Ambeprasad Kushwal et al [3]are
study the comparison of the different shaped finned heat
sink by numerical investigation and obtaining the thermal
performance as thermal resistance, pressure drop, heat
transfer rate, heat transfer coefficient, surface nusselt
number. By comparing concluded trapezoidal performs
better. Emre Öztürk [4]. He investigated the Heat sink
effectiveness, effect of turbulence models, effect of radiation
heat transfer and different heat sink geometries were
numerically analyzed by commercially available
computational fluid dynamics software Fluent for forced
cooling. The numerical results are compared with the
experimental data. Conjugate heat transfer is simulated for
all the electronic cards and packages by solving Navier-
Stokes equations. Qu and Mudawar [5] have performed
experimental and numerical investigations of pressure drop
and heat transfer characteristics of single-phase laminar flow
in 231𝜇m by 713 𝜇m channels. De ionized water was
employed as the cooling liquid and two heat flux levels, 100
W/cm2 and 200 W/cm2, defined relative to the planform
area of the heat sink, were tested. Good agreement was
found between the measurements and numerical predictions,
validating the use of conventional Navier–Stokes equations
for micro channels. For the channel bottom wall, much
higher heat flux and Nusselt number values are encountered
near the channel inlet. P.Satyamurty and P.W.Runstadler [6]
are evaluated the performances of Planar and Staggered heat
sinks with varying heat loads and with varying approach
velocities. The comparison is made by computational
method, the results obtain that Staggered shows better
thermal performance than planar heat sinks. Wang and Peng
[7] had investigated experimentally the single-phase forced
convective heat transfer characteristics of water/methanol
flowing through micro-channels with rectangular cross
section of five different combinations, maximum and
minimum channel size varying from (0.6 × 0.7 mm2) to (0.2
× 0.7 mm2). The results provide significant data and
considerable insight into the behavior of the forced-flow
convection in micro channels.
3. METHODOLOGY
Conjugate Heat Transfer analysis is applicable when there
are two adjacent regions and one need to analyze the heat
transfer between these regions. In case of heat sinks that are
attached to active components of electronic devices,
convection heat transfer occurs when air is passed over heat
fins and conduction heat transfer occurs from base plate
(heat source) to the fins. The methodology adopted in this
project for conjugate heat transfer analysis consists of the
simultaneous calculation of heat conduction in the solid and
convective heat transfer in the fluid. The heat is conducted
from the base plate to fin and then it is dissipated or taken
away from fin to the surroundings through convection
process. When air is passed over the fins, heat is dissipated
to surroundings and thus it cools the heat fins.

_______________________________________________________________________________________
The first step in the methodology followed is to solve the
incompressible Navier Stokes equations with turbulent flow
to get the pressure and velocity fields. The flow governing
momentum equations (1) with standard k-ε turbulence
model in indicial notation are given below.
𝝏(𝝆𝒌)
𝝏𝒕
+
𝝏(𝝆𝒌𝒖 𝒊)
𝝏𝒙 𝒊
=
𝝏
𝝏𝒙 𝒋
𝝁 +
𝝁 𝒕
𝝈 𝒌
𝝏𝒌
𝝏𝒙 𝒋
+ Pk + Pb – 𝝆𝝐 − YM +
Sk (1)
The next step is to solve the energy equation (2) for both
fluid and solid regions to obtain temperature distribution
along the length of the fin by applying the interface
boundary condition (3) at the coupled region.
∂T
∂t
+ ∇ ∅T − ∇ α∇T = 0 (2)
∂Tsolid
∂t
− ∇ αsolid ∇T = 0 (3)
Above equations are partial differential equations that
cannot be solved by analytically and hence one has to use
numerical techniques like finite difference method, finite
volume method to get the required solutions. Computer
simulation procedure is followed to get the required
solutions within the reasonably accepted values. For this
purpose computer simulations can be carried out using
commercially available FLUENT® software.
3.1 Governing Equations in CFD
There are mainly three equations that we solve in
computational fluid dynamics problems. They are continuity
equation, momentum equation and energy equation. These
three equations are collectively called Navier Stokes
equations. The flow of most fluids may be analyzed by
mathematically solving the last two equations. These three
equations represent the conservation of mass, momentum
and energy respectively. These three equations are
represented as below.
Continuity Equation
∂u
∂x
+
∂v
∂y
+
∂w
∂z
=0 (4)
Momentum (Navier Stokes) Equations
X-Momentum Equation
ρ u
∂u
∂x
+ v
∂u
∂y
+ w
∂u
∂z
= −
∂ρ
∂x
+ μ
∂2
u
∂x2
+
∂2
u
∂y2
+
∂2
u
∂z2
(5)
Y-Momentum Equation
ρ u
∂v
∂x
+ v
∂v
∂y
+ w
∂v
∂z
= −
∂ρ
∂y
+ μ
∂2
v
∂x2
+
∂2
v
∂y2
+
∂2
v
∂z2
(6)
Z-Momentum Equation
ρ u
∂w
∂x
+ v
∂w
∂y
+ w
∂w
∂z
= −
∂ρ
∂z
+ μ
∂2
w
∂x2
+
∂2
w
∂y2
+
∂2
w
∂z2
(7)
Energy Equation
u
∂T
∂x
+ v
∂T
∂y
+ w
∂T
∂z
=
1
α
∂2
T
∂x2
+
∂2
T
∂y2
+
∂2
T
∂z2
(8)
3.2 Problem Solving in Ansys Fluent
In this, there are mainly 3 steps for solving the problem in
hand.
1. Pre-processing.
2. Solver.
3. Post processing.
In pre- processing made the heat sink model in CATIA V5
R20.These files imported to FLUENT 14.5 workbench. In
Ansys work bench selecting the unit in millimeter. Making a
fluid body and rename to the base plate walls fins are
subtracts in the solid body from fluid body and gave the
name as inlet, outlet and walls.
Fig 2 Mesh generation

_______________________________________________________________________________________
In mesh generation element size 1 mm and checking the
skewness factor. In solver, Gauss siedel solution method is
used and solution control is retain the default and give the
solution initialization and running the hybrid run and running
the calculation. In the post processing process visualize
clearly through and we can analyze by range of color coding
like velocity vector, pressure contours and temperature
contours etc.
4. RESULTS AND DISCUSSION
The conjugate heat transfer analysis of fins is carried out by
using commercial available FLUENT® software and
turbulence module is used to account for turbulence
phenomenon. Standard k-ε model is used for turbulence
model.
Conjugate heat transfer simulation work consists of analysis
of both convection heat transfer and conduction heat transfer
processes. The air (fluid) flows over the fins at the interface
regions of both solid and fluid. The main equations are
solved for fluid flows are the momentum equations and
turbulence-modeling equations. Solution of these Navier-
Stokes equations gives the velocity vectors and pressures in
the fluid flow region. FLUENT® has capability to solve
Navier-Stokes equations with standard k-ε applied
turbulence model.
The energy equation is solved for both fluid (convection
heat transfer) and solid (conduction heat transfer) regions to
obtain temperature distribution along the length of the fin by
applying the interface boundary conditions at the coupled
region.
As the first step of the present study, the CFD results have to
be validated against analytical values or experimental values
or previous literature data.
The overview of the results of present study involves CFD
validation and parametric study conducted for different
configuration of fins at a constant velocity 3.933 m/s in a
duct. And made comparison with zig zag, fluted, slanted
mirror, custom pin fin and staggered fin configuration
models.
Table1. Variation of Thermal Performance of Heat Sink
Fin profile Heat
Load
(W)
Surface heat
transfer
coefficient
(W/m2
k)
Max.
Temp
(k)
Thermal
Resistance
(K/w)
Total
Pressure
Drop
(pa)
Surface
Nusselt No
50 154.44 338.2 0.8000 19.75 6380
Zigzag Array 75 166.77 358.6 0.8080 19.88 6889
100 173.52 379.3 0.8130 26.40 7170
50 153.76 332.1 0.6820 21.34 6350
Fluted Array 75 167.21 349.2 0.6826 21.49 6910
100 174.55 366.5 0.6851 28.84 7212
50 215.55 316.4 0.3680 21.34 8913
Slanted
Mirror
75 215.21 325.6 0.3681 21.33 8891
Array 100 215.72 334.9 0.3690 23.28 8906
50 130.54 313.5 0.3100 119.04 5393
Custom Pin
Fins
75 156.61 321.2 0.3093 119.81 6470
100 175.25 329.0 0.3100 119.873 7239
50 129.63 329.4 0.6280 22.19 5949
Staggered
Array
75 144.01 345.2 0.6293 22.46 6299
100 152.41 361.1 0.6310
22.68
5357
From the table 1 it is observed that slanted mirror fin array
gives the almost constant heat transfer a coefficient value
that is highest among all other fin configurations. Thermal
resistance is minimum for custom pin fins but gives higher
pressure drop. In the other hand zigzag fin configuration
gives lowest pressure drop. Slanted mirror array is decided
as best fin configuration which gave consistent higher heat
transfer coefficient with reasonable low pressure drop.
Slanted mirror array geometry temperature, pressure and
velociy contour for 50 W

_______________________________________________________________________________________
Fig .3 Temperature contour
Fig .4 Pressure contour
Fig .5 Velocity contour
5. CONCLUSION
In this Project work, numerical analysis of different fin
geometries of heat sinks for forced convection heat transfer
and their comparison carried out by using CFD technique.
Five different fin geometries were created and effect of heat
load on thermal performances are studied and presented
through graphs and contours.
For all five fin geometries compared for the maximum
temperature attained on the basis of result governed by the
CFD and conjugative heat transfer analysis. With fin space
2.8 mm Slanted mirror array geometry of heat sink model
shows that lowest maximum temperature attained compared
to Zigzag, Fluted and Staggered array geometry of heat sink.
Zigzag shows maximum temperature attained, which is not
desirable and Custom pin fin model shows lowest maximum
temperature attained with high pressure drop, which is not
desirable. Surface heat transfer coefficient and surface
Nusselt number is maximum in Slanted mirror array heat
sink with different heat loads of 50 W, 75 W and 100 W.
As per criterion for selection of heat sink, the heat sink
should have lowest Thermal resistance, low pressure drop
and maximum surface heat transfer coefficient.
The Slanted mirror array heat sink shows the lowest thermal
resistance and maximum surface heat transfer coefficient
with low pressure drop. It has the lowest maximum
temperature attained compared to other fin geometry heat
sink models and with best surface nusselt number for a
given heat load of 50 W, 75 W and 100 W.
Slanted Mirror Array fin geometry heat sink shows the best
thermal performances and fulfills criteria for selection of
heat sink compared to other geometries of heat sink models
and it is manufacturable and producible
ACKNOWLEDGEMENTS
My heart full thanks to our beloved HOD and my Guide
Dr.V.M.Kulkarni who patronized and encouraged me in
carrying out this Dissertation work successfully.
REFERENCES
[1] C. L. Chapman, S. Lee, and B. L. Schmidt, “Thermal
Performance of an Elliptical Pin Fin Heat sink,”
Proceedings of the Tenth IEEE Semiconductor
Thermal Measurement and Management Symposium
(Semi-Therm), San José, California, February 1-3,
pp. 24-31, 1994.
[2] Denpong Soodpadhkee, Masud Behnia and Watabe,
„A comparison of heat sinks in Laminar forced
convection: part I- Round, Elliptical, and Plate Fins
Staggered and Inline configuration‟. IJMP – Volume
24 NO-1, in 2001.
[3] Ambeprasad Kushwaha and Prof. Ravindra Kirar,
„Comparative study of Rectangular, Trepezoidal and
Parabolic shaped Finned Heat sink‟. IOSR – 2278-
1684 Volume 5 Issue 6 – Apr 2013.
[4] Ozturk‟ E (2004). CFD Analysis of heat sinks for
CPU cooling with FLUENT. M.S thesis, Middle East
Technical University, Ankara, Turkey.
[5] Qu, W. and Mudawar, I. 2002. Experimental and
numerical study of pressure drop and heat transfer in
a single-phase micro-channel heat sink. International
Journal of Heat and Mass Transfer. 45, 2549 – 2565.

_______________________________________________________________________________________
[6] P. Sathyamurthy, P.W. Runstadler, and S. Lee,
“Numerical and Experimental Evaluation of Planar
and Staggered Heat Sinks,” Proceedings of the Fifth
InterSociety Conference on Thermal Phenomena in
Electronic Packaging (Itherm), Orlando, Florida,
May 28 – June 1, pp. 132-139, 1996.
[7] Peng, X. F., Wang, B. X., Peterson, G. P., and Ma, H.
B. 1995. Experimental investigation of heat transfer
in flat plates with rectangular micro channels.
International Journal of Heat and Mass Transfer.
38,127-137.

Cfd and conjugate heat transfer analysis of heat sinks with different fin geometries subjected to foced convection used in electronics cooling

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Cfd and conjugate heat transfer analysis of heat sinks with different fin geometries subjected to foced convection used in electronics cooling

Similar to Cfd and conjugate heat transfer analysis of heat sinks with different fin geometries subjected to foced convection used in electronics cooling (20)

More from eSAT Journals

More from eSAT Journals (20)

Recently uploaded

Recently uploaded (20)

Cfd and conjugate heat transfer analysis of heat sinks with different fin geometries subjected to foced convection used in electronics cooling