1

www.glacialtech.com

Geometry Parameters Analysis

of CPU Heat Sinks

GlacialTech, INC.

27th September 2002

2

www.glacialtech.com

To understand the effects of the geometry parameters for aluminum extrusion fins, we employed PHOENICS and experimentation to prove the results each other. The parameters are:

the ratio of thickness and pitch between fins

fin number

length for heat sink

height of fins

Introduction

3

Phoenics simulation

VR-EDITOR1. Build physics module2. B.C. setting 3. Phoenics setting

EARTH（ Iteration）

Convergence

Yes

No

VR-VIEWERGenerate temperature、 velocity and pressure field

Decide the geometry parameter of heat sinks

Manufacturing extrusion fins

Check thermocouple

Keep environment temp. is 35℃

Steady

Yes

No

Measure CPU temp.

1.Calculate thermal resistance2. Discussion of results

Experimentation

Flowchart for the research

4

www.glacialtech.com

Physics model

environment temp. is

35 ℃

heat flux is 45 W

Flow rate is 17 CFM

5

www.glacialtech.com

PHOENICS Setting

steady state

elliptic – staggered formulation

cartesian coordinate system

the fluid is incompressible

k-ε turbulence model

convergence criterion is 0.1 ﹪

no heat flux in heat sink

6

www.glacialtech.com

Insulate

Insulate Insulate

Fan

Heat Sink Copper

Computer Display

Power supply

Th

erm

al Co

up

le

Insulate

Insulate Insulate Fan

Heat Sink

Computer & Data

Acquisition Board

Power Supply

Ambient Temperature = 35¢XC

Heat Source

(Copper or CPU)

Thermal Couple

Pressure Load

Closed Chamber

Experimentation

7

www.glacialtech.com

Discussion :Ⅰ

785.01092.11036.3104.7 13243 xxxyblue line:

green line:

9156.110294.810256.2104.2 22335 xxxy

The ratio of thickness and pitch between fins

Fin number

p: pitch of fins

t: thickness of fins

We have better performance in more fins in the same ratio of p/t.

8

www.glacialtech.com

Discussion :Ⅱ Length for heat sink

1047.11094.3109.7 325 xxy

The effect of increasing length of heat sinks is not apparent for decreasing thermal resistance.

The good value of length of heat sink is about 75 mm.

9

www.glacialtech.com

Discussion :Ⅲ Height of fins

412234 101.110111.210136.110711.1 xxxy

When the height of fins is less than 20 mm, thermal resistance has large drop.

10

www.glacialtech.com

Conclusion and Development

1. Thermal resistance will decrease when thickness were increased, but

increasing fin number has bigger effect than increasing thickness of fins.

2. Increasing height of fins will provide good solution but increasing

length of heat sinks is not apparent for decreasing thermal resistance.

3. We will build a system which will help us to design extrusion fins

quickly in the future.

4. General extrusion ratio is 20 now, but the ratio in GlacialTech is 28, so

to promote extrusion ratio is our purpose in the future.

11

www.glacialtech.com

•Power dissipation=70W

•Environment Temp. = 35℃

•Flow rate = 13.3CFM

•Noise=25 dB •Thermal Resistance=0.357 ℃/W

Application