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Heat sink analysis using COMSOL Solver. (A tutorial guide)

Kaleeswaran.B

M.Tech (CFD); Dept. of Aerospace.

University of Petroleum Energy Studies

Dehradun, India

kaleesmach@gmail.com

Abstract—In this paper COMSOL multiphysics analysis of

heat sink in an aluminum material is shown. Various steps

involved in it are explained and diagrammatic version of it is also

explained.

Keywords: COMSOL, Multiphysics,

I. INTRODUCTION.

In COMSOL multiphysics analysis involves three steps;

1. Sequencing – the methods done are saved in a step

wise tree method. Thus, during every part of the

training the step can be viewed and can be changed if

on wishes.

2. Selection of materials: in this the material one wishes

to add, could be added and its properties could be

studied.

3. Use of selections: to define the boundaries, initial

conditions and other steps of the modeling process.

The modeled system consists of an aluminum heat sink for

cooling of components in electronic circuits mounted inside a

channel of rectangular cross section. Such a set-up is used in

order to measure the cooling capacity of heat sinks. Air enters

the channel at the inlet and exits the channel at the outlet. The

base surface of the heat sink is kept at a constant temperature

through an external heat source. All other external faces are

thermally insulated.

Figure1: Model of the heat sink with the boundaries.

II.ABOUT THE MODEL.

The cooling ability of the heat sink is determined by the

power required to keep the base of the surface at a constant

temperature. The model solves the concept of thermal

balance.Actually,the thermal energy is transported through the

conduction, convection in the heat aluminum sinks. The

temperature field is made continuous throughout the model.

The temperature is set at the inlet of the channel and at the

base of the heat sink. The layer can also be sliced to view the

model in layers.. In such case, you have to define a heat

transfer coefficient for the adhesive layer and then set the

temperature at the heater side of the layer. The transport of

thermal energy at the outlet is dominated by convection.

The flow conditions are solved by taking momentum and

mass conservation equations. The flow field is obtained by

solving one momentum balance for each space coordinate (x,

y, and z) and a mass balance. The inlet velocity is defined by a

parabolic velocity profile for fully developed laminar flow. At

the outlet, a constant pressure is combined the assumption that

there are no viscous stresses in the direction perpendicular to

the outlet. At all solid surfaces, the velocity is set to zero in all

three spatial directions. The thermal conductivity of

aluminum, the thermal conductivity of air, the heat capacity of

air, and the air density are all temperature-dependent material

properties.

III.PROCESS/METHODS

i. First step involves click on MODEL WIZARD. In

model wizard click add physics tree> click on the Heat

transfer>conjugate heat transfer>laminar flow (nitf).In the

studies click preset studies>stationery>OK (finish).

ii. Second step click on the GLOBAL DEFINITIONS.

The global definitions are located in the model builder

window. GLOBAL DEFINITIONS > click on the

SETTINGS in the parameter window and enter the

following settings;

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S.no Name Expression Description

1 L channel 7 Channel length

2 W channel 3 Channel width

3 UO 5 Inlet velocity

4 H channel 1.5 Channel height

Table: 1.Global settings parameters

iii. Third step involves defining the GEOMETRY.

Right click on the model I> GEOMETRY I and IMPORT.

Go to settings window> browse and click import HEAT

SINK model and click on the build selected button.(actually

strictly speaking U can use this import facility only when U

install the COMSOL setup. The import model is already a

finished CAD model stored in the COMsol setup).

Figure: 2.Model selected with domain as air.

IV. Now, right click on the Geometry I and then click

WORKPLANE I. Now, under the work plane I > click on

the geometry and then click RECTANGLE. Now, go to

settings window for rectangle.

Width of the rectangle = L channel.

Height of the rectangle = W channel.

Position section of the rectangle along X axis = 4.5e-02.

Position section of the rectangle in Y axis = W channel/2.

Figure:3.Model selected with inner domain aluminum

V. In the Model Builder window, right-click Work

Plane and choose Extrude. Right-click Extrude and choose

Go to Default 3D View. Go to the Settings window for

Extrude. Locate the Distances from Work Plane section. In

the table, enter the following settings:

Enter the Distance as H channel

Click the Build Selected button.

VI. MATERIALS:

In the Model Builder window, right-click Model

1>Materials and choose Open Material Browser. Go to the

Material Browser window, locate the Materials section. In

the Materials tree, select Built-In>Air. Right-click and

choose Add Material to Model from the menu. Air By

default, the first material you add applies to all domains.

Typically, you can leave this setting and add other materials

that override the default material where applicable. In this

example, specify aluminum for Domain 2.Use Aluminum

AH 3003-H18.

VII.CONJUGATE HEAT TRANSFER:

In the Model Builder window, right-click Model

1>Conjugate Heat Transfer and choose Fluid. Select

Domain 1 only.

Figure :4.Conjugate heat model.

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1. In the Model Builder window, right-click Conjugate Heat

Transfer and choose Laminar Flow>Inlet.

2. Select Boundary 115 only. Go to the Settings window for

Inlet. Locate the Boundary Condition section. From the

Boundary condition list, select laminar inflow.

Figure: 5.Inlet condition chosen model

3. In the U (average velocity) field edit field, type U0. In the

Model Builder window, right-click Conjugate Heat Transfer

and choose Laminar Flow>Outlet.

4. Select Boundary 1 only. In the Model Builder window,

right-click Conjugate Heat Transfer and choose Heat

Transfer>Temperature.

5. Select Boundary 115 only. In the Model Builder window,

right-click Conjugate Heat Transfer and choose Heat

Transfer>Temperature.

6. In the Model Builder window, right-click Conjugate Heat

Transfer and choose Heat Transfer>Temperature.

7. Select Boundary 8 only. Go to the Settings window for

Temperature. Locate the Temperature section. In the T0 edit

field, type 393.15 K.

8. In the Model Builder window, right-click Conjugate Heat

Transfer and choose Heat Transfer>Outflow. Select

Boundary 1 only.

VII.MESH:

1. In the Model Builder window, right-click Model 1>Mesh

and choose Free Tetrahedral. In the Model Builder window,

right-click Study and choose Compute.

2. Create a selection to use for defining a data set in the

Results branch. In the Model Builder window, right-click

Mesh 1>Free Tetrahedral 1 and choose Size.

Figure :6.Fine tetrahedral mesh

3. Go to the Settings window for Size. Locate the Geometric

Scope section. From the Geometric entity level list, select

Domain.

4. Select Domains 1 only. 5 Locate the Element Size

section. From the Predefined list, select Finer. 6 Click the

Build All button.

IX. Study Definitions:

1. In the Model Builder window, right-click Model

1>Definitions and choose Selection.

2. Go to the Settings window for Selection. Locate the

Geometric Scope section. From the Geometric entity level

list, select Boundary.

3. Right-click Selection 1 and choose Select Box.Select

Boundaries 3 and 5–114 only.

X.RESULTS:

1. Data Sets, in the Model Builder window, right-click

Results>Data Sets>Solution and choose Add Selection.

2. Go to the Settings window for Selection. Locate the

Geometric Scope section. From the Geometric entity level

list, select Boundary.

3. From the Selection list, select walls. 3D Plot Group .In

the Model Builder window, click Surface .Go to the Settings

window for Surface. Locate the Coloring and Style section.

From the Color table list, select Thermal.

4. In the Model Builder window, right-click 3D Plot Group

1 and choose Arrow Volume. Go to the Settings window for

Arrow Volume. In the upper-right corner of the Expression

section, click Replace Expression.

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5. From the menu, choose Conjugate Heat Transfer

(Laminar Flow)>Velocity field (u, v, w). Locate the Arrow

Positioning section. Find the x grid points subsection. In the

Points edit field, type 40.

6. Find the y grid points subsection. In the Points edit field,

type 20.

Figure: 7.Heated vector-temp plots over the heat sink

7. In the Coordinates edit field, type 5e-3. Right-click Arrow

Volume 1 and choose Color Expression. Go to the Settings

window for Color Expression. In the upper-right corner of the

Expression section, click Replace Expression. From the menu,

choose Conjugate Heat Transfer (Laminar Flow)>Velocity

magnitude. Click the Plot button.

This will produce th required vector plots and the much

required contour plots of the heat sink model.

Figure 9.Sliced model of the temperature plot.

Figure 10.Zoomed view of the sliced model.

Figure: 8.Zoomed view of the temperature vector plots Figure 11.Top view of the heat sink model.

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XI.CONCLUSION:

Figure 7 shows the temperature vector plot of velocity over

the model. A region of high temperature can be seen near to

the model. After crossing the model the temperature of the

high velocity air reduces. A zoomed view of the vector plot is

also shown, in that a region of circulation occurs near to the

model. This causes the pressure to reduce and thus reducing

the temperature increment also.

Figure 9, 10 Sliced view models shows that the temperature

plots near and far from the models. It shows that there occurs a

region of high temperature before the model and near to the

model. After the model the heating effect of the air reduces

much.Thus,the model really acts as a heat sink