FLOW SIMULATION TO STUDY THE EFFECT OF FLOW TYPE ON … · FLOW SIMULATION TO STUDY THE EFFECT OF...

N.V.S. SHANKAR* et al. ISSN: 2250–3676

[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-2, 233 – 240

IJESAT | Mar-Apr 2012

Available online @ http://www.ijesat.org 233

FLOW SIMULATION TO STUDY THE EFFECT OF FLOW TYPE ON THE

PERFORMANCE OF MULTI – MATERIAL PLATE FIN HEAT SINKS

N.V.S. Shankar1, Rahul Desala

2, VeerlaSrinivas Babu

3, P. Vamsi Krishna

4, M. M. Rao

5

1Asst. Professor, Dept. of Mechanical Engg., SCET, AP, India, [email protected]

2Graduate Student, Dept. of Mechanical Engg., SCET, AP, India, [email protected]

3Graduate Student, Dept. of Mechanical Engg., SCET, AP, India, [email protected] 4Associate Professor, Dept. of IPE, GITAM University, AP, India, [email protected]

5Principal, SCET, AP, India, [email protected]

Abstract

Heat Sinks, in Electronic systems, are devices that cool the hotter body by dissipating the heat to a fluid medium, generally air. These

are used to cool devices such as high-power semiconductor devices, and optoelectronic devices such as high power lasers and light

emitting diodes (LEDs). These are primarily heat exchangers that are used to exchange the heat from the component to the

surroundings so as to avoid the problem of overheating. There are different types of heat sinks 1.Extruded heat sinks 2.Flooded-fin

heat sinks 3. Integrated vapour chamber heat sinks. The most effective heat sink is the one which can dissipate a large amount of heat.

In this paper, numerical simulation using CFD techniques is carried out for different types of heat sinks. Multi-material heat sink in a

computer cabinet is considered so as to study their performance under different flow conditions. Assembly model of cabinet is initially

generated. Motherboard, Rams, Chipset, Chipset heat sink, Processor heat sink and the rest of the components are modelled and then

assembled to the cabinet. A total of 180W maximum heat dissipation was given as input for analysis. The total heat consisted of heat

profile of the processor, 20W heat dissipation each for Ram and chipset. 80mm axial flow fans with 80cfm were used for inlet and

outlet air exits. 40 mm fan was modeled on the chipset and 80mm fan on the processor. Full case flow simulation was carried out and

the results were presented.

Index Terms: Heat Sink, Flow Simulation, Full Case Flow Simulation, CFD.

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1. INTRODUCTION

The advancements in computing technology led to higher data

processing rates at tremendous speeds and smaller form factor.

This is leading to higher processor temperatures and thus

higher heat dissipation requirement. Higher processor

temperatures lead to malfunctioning of CPU. Thus the major

problem in electronic systems may be defined as increasing

the performance of the processor while keeping the

temperature to a minimum extent. Thus better ways for heat

dissipation are required. Many cooling solutions [1] like using

heat pipes, water cooling and even cooling by using liquid

nitrogen have been developed.

The main criteria to be considered when designing an air

cooled heat sink is the effective utilization of the fin surface

for transfer of heat from a relatively small heat source like

CPU (with large heat generation rate) with high heat flux. The

technological advancements have led to increase in heat loads.

Thus better heat conductors such as copper plates, carbon –

carbon composites [1], doped Aluminum [10, 11] are used to

improve heat spreading from the heat source into heat sinks.

The type of heat sink and air flow in the heat sink also affect

the amount of heat dissipation. Material used for the heat sink

is another important factor that influences the efficiency of the

heat sink.

A desktop computer CPU is a complex system involving a lot

of heat transfer. Processor, Chipset and Rams are considered

as major heat sources. Experimental testing for study of heat

dissipation in a computer cabinet is a costly affair. Thus

prediction of flow pattern is of great interest as it helps in

studying the heat dissipation process. While designing a

desktop, full case flow simulation is very much necessary to

understand the flow pattern and heat transfer happening in the





system. This data can be used for optimizing the design for

better heat transfer.

R. Mohan,et al [1] discussed the process of optimizing the pin

fin and slot parallel plate fin heat sink for thermal

performance. Thermal performance when using copper and

carbon-carbon composite material for heat base were

presented in their work. Dong-Kwon, et al [2] experimentally

compared the performance of plate-fin and pin-fin heat sinks

subjected to impinging flow. Jei Wei [3] gave an overview of

the thermal design and cooling technology development of

Fujitsu’s high performance servers. Thermal management is

outlined in terms of server cabinet, system board and CPU

package. The challenges before cooling solutions were also

discussed. Chyi-Tsong Chen, et al [4] demonstrated how FEM

and GA can be together applied to optimize the shape of heat

sink for better heat dissipation. Takeshi hirasawa, et al [5]

addressed the problems in manufacturing heat sinks that rise

due to size, shape and materials being used.

Flat micro heat pipes are now being used in lot of applications

like personal computers. Yuichi Kimura, et al [6] presented

the results of steady state analysis on flat micro heat pipe. The

steady-state heat transfer characteristics of this heat pipe have

been experimentally confirmed in detail, and a prediction

method for its maximum heat transfer rate is proposed.

Sukhvinder Kang, et al [7] presented a physics based

analytical model to predict the thermal behavior of pin fin heat

sinks in transverse forced flow. Giovanni Cortella[8] showed

how CFD can be used in refrigerator systems design. Ram

Viswanath, et al [9] addressed the multidimensional problem

in which materials and process improvements in packaging

and heat-sink technology are required to minimize thermal

resistance while maintaining an optimal cost for the thermal

solution. Keller and Kurtis [10, 11] discussed the advantages

of using cast heat sinks of aluminum doped with zinc. Tom

Kowalski, et al [12] discussed the use of FNM and CFD to

design the complex electronic cabinet used for high speed

internet connection. M. Davis, et al [13] discussed the use of

thermoelectric materials in cooling solutions for heat sources

of small form factors.

In the present work, performance comparison of multi-

material plate fin heat sink with copper base and aluminum

plate fins, located in a desktop computer as shown in fig 1,

during flooded and impinging flow is presented. A total of

180W heat dissipation is planned. The heat profile of

processor [15, 16], 20W heat dissipation from Ram and

Chipset [1] were given as input. A full case flow simulation is

carried out and the results are compared. Processor

temperature is the important factor considered in present work.

Figure 1: Modeled cabinet with processor, heat sink and

Ram (one side cover plate was made transparent for

showing inner parts)

2. HEAT SINK TYPES Different types of heat sinks have been designed as cooling

solution for heat dissipation problem. These heat sinks are

classified based on various criteria. The classification of heat

sinks is presented in fig 2.

Figure 2: Heat sink classification

When air is forced to flow over the fins by use of a special fan

on the heat sink, then it is called as active heat sink. Figure 3

shows an active heat sink. When no extra fan is used for

circulating air over the fins and the air circulation is purely

due to the case fan, the heat sink is referred as passive. Figure

Heat Sink

Extruded

Flooded

Integrated

Vapour

Chamber

Active

Passive





4 shows a passive heat sink. Passive heat sinks are generally

seen on north bridge chipset in common home desktops.

Figure 5 shows an integrated vapor chamber heat sink.

Figure 3: Active and flooded heat sink

Figure 4: Passive heat sink on a mother board

Figure 5: Integrated Vapour Chamber heat sink

In addition to the above classification, heat sinks are further

classified as extruded, flooded and Integrated Vapor Chamber

heat sinks.

Extruded heat sinks are generally made by extruding

Aluminum or other material. This Heat sink is a single piece.

The fins are rarely rectangular. Figure 6 shows an Extruded

Heat sink. When higher power dissipation is the requirement,

then flooded heat sinks are used. In Flooded heat sinks, the

ratio of the fin thickness to fin pitch can be as low as 1:3[9].

Figure 3 shows a flooded heat sink. It can be observed that the

fins are very close to each other. Integrated vapor chamber

heat sink, on the other hand, uses heat pipe. The problem of

resistance to heat spreading is well tackled by the usage of

heat pipes.

Figure 6: An active extruded heat sink

In present work, the heat sink considered, has a

Copper base and Aluminum plate fins. Studies are conducted

when this heat sink was subjected to flooded and impinging air

flows. The images of the heat sink models considered are

show in figures 7 & 8.

Figure 7: Designed flooded plate fin heat sink with Al fins

and Cu base





Figure 8: Designed plate fin heat sink with impinging flow,

Al fins and Cu base.

With the designed heat sinks, a full case flow simulation was

carried out and the results are presented in the next section.

3. RESULTS AND DISCUSSIONS

The chassis models with the flooded and impinging flow heat

sinks are analyzed using CFD simulation for air flow patterns

and heat dissipation. Four fans are used in simulation, of

which 2 case fans and 1 processor fan were 80 mm axial flow

with 80 cfm and other was a 40 mm chipset fan.

Two orientations of flooded heat sink i.e. parallel flow and

perpendicular flow are initially considered. When the fan of

the flooded heat sink is placed parallel to the inlet case fan, it

is observed that the temperature of the Ram is around 74oC.

The cut plot showing the orientation of the heat sink and the

flow pattern for this case is given in fig 9. Figure 10 and 11

show the flow velocity and density of air in parallel flow

pattern.

Figure 9: Cut plot showing temperature and velocity

distribution for parallel flow flooded cooler

Figure 10: Air density distribution in cabinet for parallel

flow flooded cooler

Figure 11: Air velocity distribution in cabinet for parallel

flow flooded cooler

Figure 12: Cut plot showing temperature and velocity

distribution for perpendicular flow flooded cooler





Figure 13: Air density distribution in cabinet for

perpendicular flow flooded cooler

Figure 14: Air velocity distribution in cabinet for

perpendicular flow flooded cooler

In Figures 12, 13 and 14, the cut plots containing the

perpendicular flow pattern are presented. From the above plots

it can be observed that there is higher air velocity for

perpendicular flow between rams when compared with

parallel flow. This resulted in lower temperatures for RAM. A

comparative graph of predicted temperatures of various

components in both the cases is given in fig 15. Based on the

results it can be observed that the latter is an optimum

orientation. The results of these are taken into consideration

when comparing the performance with those of impinging

flow.

Surface plots showing temperature distribution and heat flux

of the processor heat sink and chipset heat sink for this

orientation are presented in figures 16 to 18.

Figure 15: Comparison of temperatures in parallel and

perpendicular flow orientations

Figure 16: Temperature distribution on processor heat

sink with flooded flow

Figure 17: Heat flux on processor heat sink with flooded

flow





Figure 18: Temperature distribution on Chipset heat sinks

with flooded flow on processor heat sink

Figure 19: Temperature distribution on processor heat

sink with impinging flow

Figure 20: Heat flux on processor heat sink with

impinging flow

Figure 21: Temperature distribution on Chipset heat sink

with impinging flow on processor heat sink

Figure 22: Cut plot showing the air flow pattern in cabinet

with impinging flow on CPU heat sink

Figure 23: Comparison of temperature in impinging flow

and flooded flow





As mentioned earlier, CFD analysis with impinging flow on

multi-material heat sink was also performed. Figures 19 to 22

show the results of the analysis when impinging flow on heat

sink was considered. Based on the surface plots of the

processor heat sinks, it can be observed that there is a slight

lower temperature during flooded flow. A comparative plot of

temperatures of various components is presented in figure 23.

Processor temperature is the main factor of comparison as

processor is the component dissipating maximum amount of

heat in the system. Based on the plot it can be observed that

with flooded flow, the processor and Ram temperatures are

slightly lower, but the chipset temperatures are high. Based on

these observations, it can be concluded that there is

performance gain achieved using a flooded heat sink but at the

cost of increased temperature of other components. In order to

overcome this disadvantage, a better chipset fan or chipset

heat sinks are to be used.

4. CONCLUSION

A study of effect of air flow on the performance of a multi –

material heat sink, with copper base and aluminium plate fins,

using CFD analysis is performed. Two types of air flows are

considered: Flooded flow and impinging flow. Initially flow

simulation is carried for two orientations of the flooded flow

heat sink. It is found that when the heat sink is perpendicular

to the inlet case fan axis, the temperatures of all the other heat

generating components are low. Thus this orientation is

considered for comparison with imping flow configuration

results. Comparing the results of impinging flow and flooded

flow, it is observed that, there is a performance gain with

flooded flow heat sink at the cost of rise in temperature of

other components.

REFERENCES

[1] R. Mohan and Dr. P. Govindarajan, 2010, “Thermal

analysis of CPU with composite pin fin heat sinks”,

international journal of engineering science and

technology Vol.2, issue 9, pp. 4051-4062

[2] Dong-Kwon Kim, Sung Jin Kim, Jin-Kwon Bae, 2009,

"Comparison of thermal performances of plate-fin and

pin-fin heat sinks subject to an impinging flow",

International Journal of Heat and Mass Transfer 52,

pp.3510 – 3517

[3] Jie Wei, 2007, “Thermal management of Fujitsu’s High-

performance servers”, FUJITSU Sci. tech J., Vol 43 - 1,

pp.122-129

[4] Chyi-Tsong Chen, Ching-Kuo Wu, Chyi Hwang, 2008,

“Optimal design and control of CPU heat sink processes”,

IEEE Transactions on Components, Packaging and

Manufacturing Technology - TCPMT , vol. 31, no. 1, pp.

184-195

[5] Takeshi hirasawa, Kenya Kawabata and Masaru Oomi,

2005, “Evolution of heat sink technology”, Furukawa

Review No.27, pp. 25-29

[6] Yuichi Kimura, Yoshio Nakamura, Junji Sotaniand

Masafumi Katsuta, 2005, “Steady and Transient Heat

Transfer Characteristics of Flat Micro Heat pipe”, No. 27,

pp.3-8

[7] Sukhvinder Kang, Maurice Holahan, 2003, “The Thermal

Resistance of Pin Fin Heat Sinks in Transverse Flow”,

Proceedings of IPACK0, July 6–11, Maui, Hawaii, USA

[8] Giovanni Cortella, 2002, “CFD-aided retail cabinet

designs”, Computers and Electronics in Agriculture, pp.43

– 66

[9] Ram Viswanath, Vijay Wakharkar, AbhayWatwe and

VassouLebonheur, 2000, “Thermal performance

challenges from silicon to systems”, Intel technology

journal Q3, pp1-16

[10] Keller, Kurtis, 1998, "Cast 3D Heatsink Design

Advantages", IEEE ITherm '98, Seattle, WA, May 27-30,

pp. 112-117

[11] Keller, Kurtis, 1998 "Low Cost, High Performance, High

Volume Heatsinks", IEMT-Europe.

[12] Tom Kowalski and Amir Radmehr, 2000, “Thermal

analysis of an electronics enclosure: coupling flow

network modeling (FNM) and computational fluids

dynamics (CFD)”, Sixteenth Annual IEEE Semiconductor

Thermal Measurement and Management Symposium, San

Jose, CA

[13] M. Davis, R. Weymouth, P. Clarke, “Thermoelectric

CPU cooling using High efficiency liquid flow heat

exchangers”, Hydrocool Pty Ltd, Proceedings of the

COMSOL Users Conference, Taipei

[14] Asad ALEBRAHIM and Adrian BEJAN, “Entropy

Generation Minimization in a Ram-Air Cross-Flow Heat

Exchanger”,Int.J. Applied Thermodynamics, ISSN 1301-

9724, Vol.2, No.4, pp.145-157

[15] Intel® Core™ i7-900 Desktop Processor Extreme Edition

Series and Intel® Core™ i7-900 Desktop Processor Series





Datasheet, Volume 1, February 2010, Document #

320834-004

[16] Intel® Core™ i7-900 Desktop Processor Extreme Edition

Series and Intel® Core™ i7-900 Desktop Processor Series

Datasheet, Volume 2, October 2009, Document number:

320835-003

BIOGRAPHIES

N. V. S. Shankar is currently working as

Asst. Professor in Department of Mechanical

Engineering, Swarnandhra College of

Engineering and Technology,

Seetharampuram. He has a total of 8 years

work experience consisting both academic

and industrial.

Rahul Desala is currently pursuing his IV

year B. Tech. (Mechanical) at Swarnandhra

College of Engineering and Technology,

Seetharampuram affiliated to JNTU,

Kakinada.

V. SrinivasBabu is currently pursuing his IV

year B. Tech. (Mechanical) at Swarnandhra


Seetharampuram affiliated to JNTU,

Kakinada.

Dr. P. Vamsi Krishna is working as

Associate Professor in Industrial

Production Engineering Department,

GITAM Univesrsity, Visakhapatnam.

He has 10 years of experience in

teaching and research.

Dr. M. Muralidhar Rao is currently

working as Principal, Swarnandhra


Seetharampuram. He has over 32 years of

experience and has many national and

international publications. He also guided

research projects.

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