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THERMAL ANALYSIS OF CPU WITH COMPOSITE PIN FIN HEAT SINKS
R.Mohan Department of Mechanical Engineering,
Sona College of Technology, Salem-636005 Tamil Nadu, India.
Dr.P.Govindarajan
Principal and Head of Mechanical Department Department of
Mechanical Engineering,
Sona College of Technology, Salem-636005 Tamil Nadu, India.
Abstract: This paper describes about pin fin and slot parallel
plate heat sinks with copper and carbon carbon composite(CCC) base
plate material mounted on CPUs. The parameters such as fin
geometry, base plate material, base plate thickness, number of
fins, fin thickness are considered and primarily in this paper fin
geometry, base plate thicknesses, base plate materials are
optimized for improving the thermal performance of a heat sink in
the next generation. In this research work, the thermal model of
the computer system with various fin geometry heat sink design has
been selected and the fluid flow, thermal flow characteristics of
heat sinks have been studied. The plate, pin and Elliptical fin
geometry heat sinks have been used with base plate to enhance the
heat dissipation. In this study a complete computer chassis with
different heat sinks are investigated and the performances of the
heat sinks are compared.
Keywords: Forced Cooling of Electronic Devices, Computational
Fluid Dynamics, Pin fin Heat Sink and copper & CCC base
plate.
1. INTRODUCTION Todays rapid IT development like internet PC is
capable of processing more data at a tremendous speed. This leads
to higher heat density and increased heat dissipation, making CPU
temperature rise and causing the shortened life, malfunction and
failure of CPU. Electronic portable devices, especially desktop PC,
CPU have become challenging and popular nowadays. The new wave of
computer technology making a crucial impact on modern world and
desktop computer is widely employed in state-of-the-art industry.
The failure rate of electronic components grows as an exponential
function with their rising temperature. Power dissipation would be
a major bottleneck to development of the micro electronic industry
in the next 5 to 10 years. The performance level of electronic
systems such as computers are increasing rapidly, while keeping the
temperatures of heat sources under control has been a challenge.
Many cooling techniques such as cooling by the heat pipes, cold
water, and semiconductor and even by liquid nitrogen were proposed
and adopted. Liquid nitrogen cooling is very expensive and not
suitable for conventional use. Due to cost constraints,
conventional air cooling technology with a fan, heat sink
combination widely used to cool desktop computers. The air cooling
technique is always significant and worthy of further study. The
challenging aspect for improving heat sink performance is the
effective utilization of relatively large air-cooled fin surface
areas when heat is being transferred from a relatively small heat
source (CPU) with high heat flux. When the heat loads are small,
thermal conduction through aluminum plates is sufficient to spread
the heat into finned heat sinks for convection from the fins into
the air. In recent years, as the heat loads have increased, better
heat conductors such as copper plates are used to improve the
spreading of heat from heat sources into the heat sinks. To meet
the next generation, CPU needs the thermal requirements with a low
profile heat sink. Therefore new heat sinks with larger extended
surfaces, highly conductive materials and more coolant flow are
keys to reduce the hot spots. There has been much success in the
thermal design of complex electronics system using CFD. Linton and
Agonafer [13] simulated an entire desktop PC with one fan using
Phoenics code. Lee and Mahalingam [12] used flotherm code to
simulate detailed flow and temperature fields within a computer
chassis with two fans. Similar work was also done by wong and Lee
[15]. Yu.C.W and Webb.R.L [16] analyzed the flow and heat transfer
inside a computer cabinet for the high power conditions expected in
desktop computers. In this research CFD (Icepak) has
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been used to identify a cooling solution for a desktop computer.
40W PCI card, different case fan size and different ducting
positions have been studied. Chang.J.Y ,etal [4] reports the
results of CFD analysis to cool the 30W socketed CPU of a desktop
computer with minimum air flow rate and minimum heat sink size. In
this paper the methodology of CFD analysis for the heat sink, duct
design has been described and experimental procedures to validate
the predictions. David Lober [6] discussed some thermal management
considerations involved in choosing an enclosure and demonstrated
the use of CFD thermal modeling software which optimally integrated
a computer system into an existing enclosure and reduced the design
cycle time. Savithri subramanyam and Keith E.Crowe [13] described
to evaluate designs of electronic cooling heat sinks by using
thermal finite element analysis (FEA) and computational fluid
dynamics (CFD). In a system as complex as a desktop computer, CFD
is a good approach to explain various design quickly with
reasonable accuracy. This research work stands to the challenges
posed by increasing chip heat flux, smaller enclosures, and
stricter performance and reliability standards. All of the changes
expected in future desktop factors will make air cooling of the CPU
more difficult. In this paper the heat sink with base plate and
fan, proper vents for air flow are designed and implemented for
better performance. In this study, various geometry heat sink with
base plate is used to cool central processing units (CPUs) of
desktop computers are investigated.
2. CFD SIMULATION APPROACH
The CPU heat sink with base plate is attached to the CPU
together with a fan. The mainboard and all the other components are
enclosed in a chassis. There are many other heat sources in
addition to CPU. Some of them are on the mainboard (e.g.,
northbridge chip), some of them are attached to the mainboard
(e.g., memory modules) and some of them are in the chassis volume
(e.g., DVD).
2.1. CFD chassis model
The CFD 3D chassis model is shown in figure 1. The chassis is
modeled using standard dimensions of a common ATX chassis by hollow
blocks and internal components are represented as lumped objects.
During modeling, all the components inside the chassis are standard
sized components and exact dimensions are obtained by measurement.
The CPU is modeled as a 2D area which dissipates 80W. The 25mm x
25mm cross sectional area of CPU is taken which is commercially
available AMD CPU. For simplicity, the mother board, chipset card
are modeled as zero thickness with heat generated uniformly. The
CPU fan is modeled as a lumped parameter model and does not have
blades. Ram cards are fixed on the motherboard. They are also heat
sources and accurate dimensioning of space between ram cards is
difficult. Therefore these things are not considered for study.
Power supply is a very complex geometry which includes lot of
electric components, wiring and heat sinks. It is assumed as a
lumped media which exerts a resistance on the cooling air flow
streams. SMPS (Switch Mode Power Supply) and few miscellaneous
cards are modeled and lots of small electronic components on these
cards are not modeled.
Fig. 1 Computer Chassis model
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The computer cases have small holes which are used to allow
inlet air for cooling and discharge hot air through outlet. The
modeling of these holes in accurate dimensioning is difficult and
computationally expensive. Therefore it is modeled as a zero
thickness flow resistance. The HDD (Hard Disk Drive), DVD, CD are
modeled as solid blocks generating a specified amount of heat
uniformly inside the volume. The closer view of geometric details
of the CPU heat sink is shown in the Figure 1. The scope of this
study is investigation of temperature distributions on CPU heat
sinks. The thermal boundary conditions for the objects inside the
chassis are listed in table1 and 2.
TABLE 1
Interior Conditions
Object name Material Heat dissipation Rate(w) CPU Silicon 80
CPU Heat sink Al Cu -
CD Al 15 DVD Al 15 HDD Al 20
POWER SUPPY Porous 75 Miscellaneous Card FR4 20
TABLE 2
Fan Conditions Name of the Fan Pressure Rise Heat Flow Rate
CPU Heat sink fan
30 Pa
30CFM
Case Fan 40 Pa
40CFM
A total of 225W of heat is dissipated. The fans inside the
domain are modeled as circular surfaces which add momentum source
to the flow. The added momentum source is given as the pressure
rise across the fan versus the flow rate curve. The relationship
between the pressure and the flow rate is taken linearly. The
boundary condition for the power supply is different. The power
supply is geometrically very complicated. Therefore it is modeled
by simplifications. The power supply is a rectangular box which is
a resistance to flow. The resistance is different in y-direction. A
closer view of surface grid on one of the CPU heat sink is shown in
figure 2.
Fig.2. Surface grid on one of the CPU heat sink
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2.2 Governing Equations Time-independent flow equations with
turbulence are solved. The viscous dissipation term is omitted.
Therefore, the governing equations for the fluid flow and heat
transfer are the following form of the incompressible continuity
equations, Navier stokes equations x-y and z direction momentum,
and energy equations together with the equation of state. The
continuity Equation
The X, Y, Z Momentum Equations
The Energy Equation
Equation of state
P= Where is the density, u, v and w are velocity components, v
is the velocity vector, P is the pressure, B terms are the body
forces, h is the total enthalpy and terms are the viscous stress
components. The Reynolds averaging is employed to handle the
turbulence effects. In the Reynolds averaging, the solution
variables are decomposed into mean and fluctuating components. For
the velocity components u = u + u , where u and u are the mean and
fluctuating velocity components for x direction. Likewise, for the
pressure and the other scalar quantities = + where is a scalar such
as pressure or energy. The Reynolds Averaged NavierStokes (RANS)
equations are solved together with the Boussinesq approximation.
2.3. Boundary Conditions While the NavierStokes equations are
solved inside the domain, no-slip boundary condition is applied to
all the walls in the domain. Therefore, at all of the surfaces u =
v = w =0. It is assumed that the system fan does not drive a flow
cell around the computer chassis and the heat transfer mechanism at
the chassis outer walls is natural convection. Heat transfer
coefficients at the outer walls are estimated from the empirical
correlations. In order to use the correlations, the average wall
temperature must be prescribed. To do that, a first cut analysis
must be run. As the typical values of the natural convection heat
transfer coefficient lie between 2 and 25 W/ m2 K , a value of 5 W/
m2 K is selected to be the heat transfer coefficient at the
computer chassis walls. The analysis results by taking the ambient
temperature as 27 C gives an average temperature of 33 C at the
walls, and then heat transfer coefficients are calculated using
this value and the available correlations with the uniform surface
temperature assumption, and with the definitions of the Rayleigh
number and the average Nusselt number as:
Ra = ; Nu =
Where is L the characteristic length, k, h, g, , and are the
fluid thermal conductivity, the convection heat transfer
coefficient, the gravitational acceleration, the volumetric thermal
expansion coefficient, the thermal diffusivity, and the kinematic
viscosity respectively. Ts and T are the surface and the ambient
temperatures. Here, Ra is less than 109, therefore, the flow is
laminar. Using the correlations for laminar natural convection on
the vertical plate by taking the thermal conductivity of air as k =
0.027 W/ m K , the heat transfer coefficient, 4 W/ m2 K. Similarly,
for the horizontal top plate the Rayleigh number is calculated as
1.5 x 105 , where the characteristic length is calculated from
AL
p , where A is the plate surface area, and P is the plate
perimeter. The average Nusselt
number is correlated to the Rayleigh number with Nu = 0.54
Ra0.25 which gives 0.04 W / m2 K . The calculated heat
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transfer coefficients are applied to all of the exterior walls
of the chassis except the bottom horizontal wall which sits on the
ground that is considered to be adiabatic. 2.4 Convergence issues
The persistent results are obtained from only a well converged,
well posed and grid independent simulation. The order of magnitude
residuals drop is used for convergence. Two different convergence
tolerances are compared, one is 10-3 for flow and 10-7for energy,
and the other is 10-4 for flow and 10-8 for energy. Running the
solver such that residuals fall one more order of magnitude means
that more iteration is done to improve the solution quality. It
should be noted that, convergence criteria must assure that the
results do not change as the iterations proceed. There is a common
way of implementing this. Scalar change of some values like
temperature is displayed as well as the residual monitors. When the
scalar values stay at a certain number and do not change as the
iterations continue, then it can be stated that the solution is
converged. It was seen that this trend is achieved when the
momentum residuals fell below 10-4and energy residual fell below
10-8 .Therefore in this paper all the models use the convergence
criteria of 10-4for the flow variables and 10-8for the energy. Emre
Ozturk and Ilker Tari was used the convergence criteria of 10-4for
the flow variables and 10-7for the energy. 2.5. Discretization
Fluent uses the finite volume method, and error arises due to
discretization of the governing equations. Interpolations are made
to find values at the cell faces, whereas all the information is
stored at the cell centers. Interpolations have to be done for
discretization. There are numerous schemes, and the easiest one is
the first-order upwinding. The advantage of this scheme is that it
converges easily. The disadvantage is that it is only first-order
accurate. It is suggested to use second-order schemes for
unstructured grids. In our cases, the first-order upwinding are
used for simulation. But Emre Ozturk (2007) used the first order
and the second order upwinding schemes. It is suggested that the
ranges of the local temperature values on the heat sink are similar
in both cases; therefore, the first-order method is computationally
less costly is used in all simulations. 2.6. Grid Selection The
mesh is the key component of a high quality solution. The total
number of cells generated is kept around 1.167 million for the
entire model. The Tetrahedral / Hybrid element scheme T grid type
meshing is used in this simulation. The only way to establish grid
independent solutions is to setup a model with a finer mesh and
analyze it to see if there are major differences in scalar
quantities and vectors. Emre Ozturk (2007) is used 1.5 million
cells. The results are compared with the default 900 000 cell
model. The mesh density increase mostly concentrated within the
nonconformal mesh around the heat sink. From the results the
temperature distributions are similar. Emre Ozturk is suggested
that 900 000 cells are enough for the models to be grid
independent. The density distribution of the mesh is concentrated
around the CPU heat sink, for example in the Elliptical heat sink
with base plate case has 0.511 million cells out of 1.167 cells are
in the nonconformal mesh of the heat sink. 2.7. Turbulence Modeling
and Radiation Effects The default turbulence model of all
calculations is the algebraic turbulence model. It is the
computationally least expensive one since no extra equations are
solved in addition to continuity, momentum, and energy equations.
The RNG k- model is used as a test case. Radiation heat transfer
helped the heat sink cool by 0.2 to 0.5 K. therefore it is
concluded that radiation could be ignored for forced cooling of
CPUs. 3. HEAT SINK SELECTION The slot parallel plate fin heat sinks
in two arrays, pin fin heat sinks of variable fin thickness and
base plates are used to cool the CPU. Unfortunately, significant
modeling and run time is needed to represent small pins with
complex meshing. In the course of preliminary numerical simulation
work, three variable thickness fin geometries of same base area,
same fin height, and same fin pitch are simulated. The 54mm x 65mm
heat sink base plate size is selected for this work. The different
shape of extruded fins and a 3.5mm thick base plate is finished of
aluminum materials. In addition to enhance the heat transfer 2.5mm
to 5 mm thick copper and CCC base plate has been provided as a
spreader to conduct heat from CPU processor. For all fin geometries
2.5 mm fin pitch, 40mm fin
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height, 54mm x 65mm heat sink base plate, 5mm clearance between
the power supply and the fin tips of the heat sink at the flow rate
of 30CFM. The fin thickness is varied from 3 to 5mm for plate heat
sink model. Similarly 4 to 5mm for pin fin heat sink model. The
thermal performance of the heat sink is modeled using gambit. The
heat sink solid model in the chassis numerical model is done and
the CFD software solves the heat transfer problem for the heat
sink. The flow of air is parallel to the heat sinks and vertical
flow of air is pulled upward by a fan mounted at the top of the
heat sink with clearance.
4. RESULTS AND DISCUSSIONS
The chassis model with slot parallel plate heat sink with base
plates are analyzed by CFD simulations. The results have been
obtained by varying the heat sink model and keeping the entire
computational domain same. The three different thicknesses of heat
sink are considered with variable base plate, the 5mm CCC slot
parallel plate heat sink temperature distributions are as shown in
figure 3.
Fig 3.1Temperature distributions on 5mm thick pin fin Heat sinks
with 5mm CCC base
Fig 3.2Temperature distributions on 5mm thick Plate fin Heat
sinks with 5mm CCC base
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For all of the heat sinks, it is viewed that their centers are
the hot spots since the heat source corresponds to the closeness of
the base center. The fans installed on the heat sinks are identical
with dimensions. The fans have hubs where air cannot pass through
and it makes the center parts hotter. In the current simulations,
the swirl of the fan is not modeled since the fans are lumped
parameter models. For real cases, the center would not be as hot as
the present simulations predict, due to the swirl. It is observed
that the upper right and left part of the heat sink has lower
temperature when compared to centre part of the heat sink. This is
due to more air flow circulation in sides of heat sink and also
exhaust fan sucks the hot air which is nearer to side of the heat
sink. The cooling becomes less efficient at other sides of the heat
sink. It is observed that the conduction rate is high in CCC base
plate rather than copper base plate and also it is enhanced by
increasing the number of fins. Since for same heat source CPU the
bottom heat sink temperature is decreased for increasing number of
fins. In this work parallel plate, pin fin and elliptical fin heat
sinks with variable base plates are used and the performances are
compared. Although the heat sink dimensions are similar, CCC base
plate heat sinks enables higher conduction rates, and heat is
conducted to the whole heat sink in a more efficient way. When the
computer chassis is investigated, it is observed that only the
upper right part of the heat sink has a free path for the air flow.
Therefore, air driven by the CPU fan can travel to that side and
the effect of which can also be seen in the temperature
distributions of figure3.On the other sides of the CPU, air returns
to the proximity of the heat sink by hitting the wall, the fan
sucks the returning relatively hot air and the cooling becomes less
efficient at these sides of the heat sink as can be observed in
figure 4.
Fig 4 path lines and temperature distribution for 3mm thick
Plate fin Heat sinks
It is also observed that these results that modeling not only
the CPU- heat sink assembly but the whole chassis is important for
predicting heat sink performance. To investigate this issue
further, everything inside the chassis is fixed and the heat sink
model is changed. The mesh is kept same, to able to compare the
results with the detailed chassis model. The model with CPU heat
dissipation values also resembles the experimental setup. The air
can bounce of the chassis walls and recirculate in the chassis, but
the temperature distribution is much more symmetric compared to the
detailed whole chassis model. It is viewed that the 5 mm thick base
plate heat sinks are performed well when compared to 2.5 mm thick
base plate heat sinks. It is viewed that the CCC base plate heat
sinks are performed well when compared to copper thick base plate
heat sinks. It is noticed that the performance of heat sink is
increased by increasing the thickness of fins instead of increasing
number of fins. In the case of large number fins, it is noticed the
small pitch between fins does not permit air to cool the hottest
centre part of the heat sinks. The performance of parallel plate
heat sinks is not affected by making 1 mm slot of 20mm of plate
fin. However, the air flow path is better and heat transfer rate
does not change and if heat transfer area is decreased, then the
thermal resistance is not significantly changed. The reduction in
heat sink material and weight creates worth for the manufacture.
The heat transfer rate is enhanced by increasing thickness of fin.
The heat transfer rate is enhanced by increasing thickness of fin
up to 25% in 5mm base plate heat sink models and up to 10% in 2.5
mm base plate thickness heat sink models.
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TABLE 3 Maximum and minimum temperatures for the three heat
sinks
with Copper base plate of thickness 5 mm and 2.5mm
Slot Plate heat sink with.5 mm Cu Base plate thickness
Slot Plate heat sink with 2.5 mm Cu Base plate thickness
Fin Height 40 40 40
Fin Height 40 40 40
fin Thickness for first 20 mm
3 4 5
fin Thickness for first 20 mm
3 4 5
Second 20 mm with 1 mm slot
2 3 4
Second 20 mm with 1 mm slot 2 3 4
Fin Pitch 2.5 2.5 2.5
Fin Pitch 2.5 2.5 2.5
Air flow rate 30CFM 30CFM 30CFM
Air flow rate 30CFM 30CFM 30CFM
Pressure drop 40Pa 40Pa 40Pa
Pressure drop 40Pa 40Pa 40Pa
Temperature of base plate
327 328 332 Temperature of base plate
328 330 333
Temperature of tip of heat sink
314 316 322 Temperature of tip of heat sink
314 317 321
TABLE 4
Maximum and minimum temperatures for the three heat sinks with
CCC base plate of thickness 5 mm and 2.5mm
Slot Plate heat sink with.5 mm CCC Base plate thickness
Slot Plate heat sink with 2.5 mm CCC Base plate thickness
Fin Height 40 40 40
Fin Height 40 40 40
fin Thickness for first 20 mm
3 4 5
fin Thickness for first 20 mm
3 4 5
Second 20 mm with 1 mm slot
2 3 4
Second 20 mm with 1 mm slot 2 3 4
Fin Pitch 2.5 2.5 2.5
Fin Pitch 2.5 2.5 2.5
Air flow rate 30CFM 30CFM 30CFM
Air flow rate 30CFM 30CFM 30CFM
Pressure drop 40Pa 40Pa 40Pa
Pressure drop 40Pa 40Pa 40Pa
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Temperature of base plate
326 328 331 Temperature of base plate
327 329 331
Temperature of tip of heat sink
314 318 322 Temperature of tip of heat sink
315 318 322
TABLE 5 Maximum and minimum temperatures for the Pin fin heat
sinks
with Copper base plate of thickness 5 mm and 2.5mm
Pin fin heat sink with 5 mm Cu Base plate thickness
Pin fin heat sink with 2.5 mm Cu Base plate thickness
Fin Height 40 40
Fin Height 40 40
fin Thickness 4 5 fin Thickness 4 5 Fin Pitch 2.5 2.5
Fin Pitch 2.5 2.5
Air flow rate 30CFM 30CFM
Air flow rate 30CFM 30CFM
Pressure drop 40Pa 40Pa
Pressure drop 40Pa 40Pa
Temperature of base plate
337 339.5 Temperature
of base plate
339 342
Temperature of tip of heat sink
322 325 Temperature
of tip of heat sink
322 326
TABLE 6
Maximum and minimum temperatures for the Pin fin heat sinks with
CCC base plate of thickness 5 mm and 2.5mm
Pin fin heat sink with 5 mm CCC Base plate thickness
Pin fin heat sink with 2.5 mm CCC Base plate thickness
Fin Height 40 40
Fin Height 40 40
fin Thickness 4 5 fin Thickness 4 5 Fin Pitch 2.5 2.5
Fin Pitch 2.5 2.5
Air flow rate 30CFM 30CFM
Air flow rate 30CFM 30CFM
Pressure drop 40Pa 40Pa
Pressure drop 40Pa 40Pa
Temperature of base plate
335 338 Temperature
of base plate
338 341
Temperature of tip of heat sink
322 326 Temperature
of tip of heat sink
322 327
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TABLE 7 Comparison of Experimental and simulation results of
slot plate heat sinks
With2.5 & 5mm Copper base plate
STUDY
Parameter
2.5 MM BASE PLATE HEAT SINK MODELS
5 MM BASE PLATE HEAT SINK MODELS
Fin thickness at Bottom 3 mm 3 mm 5 mm 3 mm 3 mm 5 mm
Fin Thickness at Top 2 mm 2 mm 4 mm 2 mm 2 mm 4 mm
Fin Material Al/cu Al/cu Al/cu Al/cu Al/cu Al/cu CFD Simulation
(K)
T 14 13 12 13 12 10
Experimental (K)
T 14.65 12.3 11.3 11.5 11.6 9.6
% T ERROR -4.64 5.38 5.83 11.5 3.33 4
TABLE 8 Comparison of Experimental and simulation results of
slot plate heat sinks
With2.5 & 5mm CCC base plate
STUDY
Parameter
2.5 MM BASE PLATE HEAT SINK MODELS
5 MM BASE PLATE HEAT SINK MODELS
Fin thickness at Bottom 3 mm 3 mm 5 mm 3 mm 3 mm 5 mm
Fin Thickness at Top 2 mm 2 mm 4 mm 2 mm 2 mm 4 mm
Fin Material Al/ccc Al/ccc Al/ccc Al/ccc Al/ccc Al/ccc CFD
Simulation (K)
T 12 11 11 12 10 9
Experimental (K)
T 12.45 10.6 9.7 12.2 9.1 8.72
% T ERROR -3.75 3.636 11.8 -1.67 9 3.11
TABLE 9 Comparison of numerical and simulation results of Pin
fin heat sinks
with 2.5 & 5 mm Copper base plate
STUDY
Parameter
2.5 mm Base plate Pin fin Heat sink Models
5 mm Base plate Pin fin Heat sink Models
Fin thickness 5 mm 4 mm 5 mm 4 mm
Fin Material Al/cu Al/cu
Al/cu
Al/cu
CFD Simulation (K)
T 17 16 15 14.5
Experimental (K)
T 16.3 14.8 14.4 13.6
%T ERROR 4.12 7.5 4 6.21
TABLE 10
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Comparison of numerical and simulation results of Pin fin heat
sinks with 2.5 & 5 mm CCC base plate
STUDY
Parameter
2.5 mm Base plate Pin fin Heat sink Models
5 mm Base plate Pin fin Heat sink Models
Fin thickness 5 mm 4 mm 5 mm 4 mm
Fin Material Al/ccc Al/ccc Al/ccc Al/ccc
CFD Simulation (K)
T 16 14 13 12
Experimental (K)
T 15.2 12.8 12 11.3
%T ERROR 5 8.57 7.69 5.83
In this work base plate thickness is increased from 2.5 to 5mm
and base plate material is changed while keeping the fin lengths
constant. The difference between the maximum and the minimum
temperatures on the CCC base plate heat sink is around 9 C, where
as the copper base plate heat sink is around 10 C. It is observed
that for small thickness of CCC base plate heat sinks are performed
well rather than increasing the thickness of copper base plate. The
performance of heat sinks are enhanced, the weight reduction, space
limitation is advantages of using CCC base plate heat sinks. CCC
base plate heat sink performs well when compared to copper base
plate heat sink. By increasing the base plate thickness and
changing the material of base plate the performance of heat sink is
enhanced. It is also observed that by adding the base plate the
heat conduction rate is enhanced in place of increasing the fin
height. The performances of 2.5 mm ccc base plate heat sinks are
obviously comparable to 5 mm copper base plate heat sinks. 4.1
Comparison with experimental data This test setup is not the whole
computer chassis system, but a smaller domain, in order to simplify
the experiments. The base plate is attached to different heat sinks
models and centre of the base plate is heated with heat loads 80W.
Since the test setup is an open domain, the atmospheric temperature
is the temperature of the air blown to the heat sink. The
atmospheric air is passed around the heat sink which is heated that
is exhausted by blower and also the pressure drop has been noted.
In this setup other heat sources are not considered for simplify
the experiments. In this experimental setup the CPU fan and Exhaust
fan are not used in stead of those fans the blower is used to cool
the heat sink models. After steady state the bottom and top surface
temperatures are measured using thermocouples which are attached at
bottom base plate and top fin surfaces at different points.
Although the experimental comparison quantitatively, it would be
considered as qualitative one is shown in table
5. CONCULSION Number of fins and their distribution, fin
material and base plate thickness are investigated for enhancing
the heat dissipation rate from CPU. Improvements on heat sink
designs are possible by the use of CFD. It is possible to design a
new heat sink with suitable base plate which has better thermal
performance and uses less material using CFD simulations. The heat
sink base thickness is also a parameter for increasing the
performance of heat sink. If base plate material is selected to be
CCC rather than copper or aluminum, then the thermal resistance of
the heat sink is decreased. When the base plate thickness was
varied from 2.5mm to 5mm, the heat sink performed better. Due to
space limitations of heat sink in a computer it is not possible to
increase the height of the heat sink. Therefore, the base plate is
attached with heat sink to enhance the performance rather than
increasing the height of heat sink. In the current study, it is
observed that stacking too many fins is not a solution for
decreasing the hot spots on the heat sink since they may prevent
the passage of air coming from the fan to the hottest centre parts
of the heat sink. In this paper, three thicknesses of heat sinks
with base plate are selected and analyzed. From which the optimal
design of heat sink is selected which gives more heat transfer
rate. It is observed that the velocity field around the heat sink
is affected from the presence of the other components inside the
chassis as well as the chassis walls which redirect the hot air
back into CPU heat sink. If the heat sink is
ISSN: 0975-5462 4061
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R.Mohan et. al. / International Journal of Engineering Science
and Technology Vol. 2(9), 2010, 4051-4062
plate fin type, plate fins can reduce the recirculation. It is
also possible to increase intake of cooler air by using heat sink
fan. The CPU is considered as the largest heat source, which is
cooled directly drawing cooler ambient air from outside the chassis
to the CPU fan with a duct is a viable option that has been
recently implemented by many chassis manufacturers. The present
study together with Emre ozturk (2007) outlines the details of CFD
simulation steps for a computer chassis thermal management solution
by concentrating on CPU cooling. These results and conclusion
obtained in this present work are found to be in good agreement
with conclusion obtained by Emre ozturk (2007). In this study, it
is suggested that slot parallel plate heat sink model with CCC base
plate, especially 5mm pin fin heat sink with 5mm CCC base plate
will benefit the design engineers involved in electronic cooling.
In this study a complete computer chassis with different heat sinks
has been investigated and the performances of the heat sinks are
compared.
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