Maryam Rafaq
Aerospace Engineering Department
College of Aeronautical Engineering,
PAF Academy Asghar Khan,
Risalpur. mary.rafaq@gmail.com
Muhammad Usman
Aerospace Engineering Department
College of Aeronautical Engineering,
PAF Academy Asghar Khan,
Risalpur. yaayayooya@gmail.com
Abstract—Heat sinks is a heat exchanger that dissipates the heat into the surrounding medium , and hence cools down the devices. The main aim is to create a design such that combines high heat transfer coefficient , a low pressure drop and reasonable cost.
Keywords—extended surfaces , fins , layout and design of fins , forced convection
I.
I NTRODUCTION
The base of this project is around heat sinks which are used to cool electronic devices like CPU. A heat sink is heat exchanger that is used to cool down the device ,by dissipating the heat into the surrounding environment. This heat exchange occurs through the extended surfaces. Heat sinks are designed in such a way that it has maximum surface contact with the cooling fluid like air or some other fluid. There are a number of different design and systems of heat sinks that are used for different heat exchanger purposes. The main parameters that are considered for designing different heat sinks are design and layout of fins, material of fins , which type of fluid is used inside the heat sink for extracting heat from the fins and the process which drives the fluid .
The purpose of this study research for such a design and solutions for heat sinks that are used to cool down the CPU device. The main goal is to design a heat sink with high heat transfer coefficient , a low pressure drop and reasonable cost. compared to aluminum 1050A , which is relatively much expensive and soft metal.
Copper alloys have twice the thermal conductivity as compared to aluminum but they are more costly and denser alloys. Copper alloys are mostly used in computer systems .
And there are other alloys of silver , brass etc used for making fins.
D.
Fin shape
Metallic fins can be divided into different categories on bases of geometry and patterns . Fin shapes varying in order to make them cheap and more conductive, and different sizes. There shapes vary from rectangular to cylindrical and or any cone-shaped shape. The different shapes are shown in fig below.
II.
DEFINITIONS
A.
Extended surfaces
The term extended surface is commonly used to depict an important special case involving heat transfer by conduction within a solid and heat transfer by convection from the boundaries of the solid.
B.
Fins
Extended surface is used specifically to enhance heat transfer between a solid and an adjoining fluid. Such an extended surface is termed a fin.
C.
Fins material
The type of the material that are used to make fins in the electronic devices ,say CPU must be effect. Nowadays the material from which these fins are made of metals like aluminum and copper. These materials have different thermal conductivities.
Aluminum alloys such as 6061 and 6063 are mostly used because of there low cast and good conductivity as
Fig.1
These different shapes leads to different heat flux values.
As the heat flux coefficient is related to dimensionless parameter for relative heat transfer , Nusselt number which has direct relation with Reynolds number. Reynolds number is also a dimensionless parameter which relates to fluid velocity and viscosity. Velocity of working fluid mainly depends upon the shape by which the fluid is flowing around the fin. Therefore higher the Nusselt number higher will be the heat transfer rate and higher will be the heat flux.
E.
Fins layout
The layout of the fins is very important. These variations are involved when there is size constraints and also when the fluid flows in such a way that it has to pass over the maximum area as much as possible. The efficieny and layout of these fins are related to coefficient of heat transfer and Nusselt number.

G.
Forcing mechanism or forced convection:
In most heat sinks, the working fluid is forced over the heated area in order to increase the heat transfer. The aim of these forced mechanism is that by external sources we want to increase the cooling effect. Like fans are used in order to remove hot air , so that it quickly replaced by the cold air , and hence the cycle continues.
III.
WORKING PROCEDURE
The working principle of heat sinks are related to Fourier’s law of heat conduction. This law states that The rate at which heat is transferred by conduction, is proportional to the product of the temperature gradient and the crosssectional area through which heat is transferred. As the heat will be transferred from region og higher temperature to lower temperature region.
Fig. 2
F.
Working fluid:
As we know that working fluid passes over the fins in order to cool down the temperature. The working fluid that is mostly used is air , as it is cheap and readily available , and more over it don’t damage the electronic devices. There are some devices in which other fluids like water or refrigerants are used. They are costly and have large heat flux and are difficult to self-contain.
Extrusion - where metal is heated and pushed through a mold.
IV.
MANUFACTURING METHODS
Heat sinks are manufactured by different methods. The methods on which these different heat sinks are formed depends upon application , performance and cast. The following methods are as below:

Machining the metal.
- where a CNC machine is used to cut


Forging - where metal is heated and shaped by pressurization.

Stamping - where the metal fin is cut, and then soldered onto the base.

Skiving - where a blade is used to slice, and push up the single block of metal.
V.
PROPOSED MODEL

Fig. 3
This is proposed model of CPU heat sink. This is design and we did manual calculations to find out that whether our proposed model is valid or not. Moreover we build a matlab code to show the temperature distribution curve .
VI.
MATLAB CODE x = 0:0.0001:0.025 ; y = @(x)
((cosh(16.327*(0.025x)))/cosh(16.327*0.025))*70+
293 ; m = y(x) ; plot(x,m,'r*') z = @(x) (cosh(16.327*(0.025x)))/cosh(16.327*0.025) ; n = z(x) ; plot(x,n,'r*')
VIII.
DESIGN CALCULTIONS
Fig. 4 Temperature distribution curve
VII.
ANSYS ANALYSIS
Fig. 5 Temperature Distribution
IX.
RESULTS AND ANALYSIS
Following results were obtained from ANSYS
In Temperature Distribution

Red color shows maximum T

Blue color shows minimum T
In heat flux distribution

Red color shows max heat flux

Blue color shows mini heat flux
X.
R EFERENCES
1.
Thermal cooling enchancement techniques for electronic components.
2.
“Heat sink”- wikipedia
3.
R.Mohan and Dr.P.Govindarajan. ―Thermal analysis of CPU with composite pin fin heat sinks ,
International Journal of Engineering Science and
Technology.
4.
Deepak Gupta, Momin Nausheen, A.D. Dhale ,
CFD Analysis & Simulation of Pin Fin for
Optimum Cooling of MotherBoard

XI.
C ONCLUSION :
We have got a total heat flux of 209 KW/m^2 . It means our proposed design was correct. This model can be used in a CPU with an efficient heat transfer. Rectangular fins design was proved to be the most suitable in our case.