Tài liệu TRANSIENT and STEADY STATE THERMAL ANALYSIS OF HEATSINK Pro/ENGINEER and Pro/MECHANICA Wildfire doc

A transient thermal analysis is used to determine the temperature, heat storage and other thermal quantities in a model due to a time varying load.. All other considerations such as the

ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN TRANSIENT and STEADY STATE THERMAL ANALYSIS OF

a part A steady state analysis is commonly used as a precursor to a transient

thermal analysis to determine the initial conditions

A transient thermal analysis is used to determine the temperature, heat storage and other thermal quantities in a model due to a time varying load Because the applied load may be time dependent, the solution is time dependent All other considerations such as the type of the thermal load and the modes of heat transfer are the same as

in a steady state analysis Transient analysis is probably the most common form of thermal analysis

Problem Statement

An engineer must attach copper heat sink to a CPU The heat sink will be subjected

to a time varying 50 Watt load and a constant convection of 100W/mC

The time required to reach steady state will be determined A fringe plot of the temperature distribution after 1000 seconds will be made

Create the Heat Sink Part

Create a new part called heat_sink.prt

Edit -> Setup -> Units

Select Meter Kilogram Second (MKS)

in the Units Manager dialog box

Click on Set button

Create a block 0.062 m width X 0.08 m depth x 0.04 m height Extrude both sides

Make a cut with the dimensions shown below

Pattern the cut with increment of 0.004 m and total of 15 cuts

Create a cut to accommodate the fan at the top of the heat sink

Create another cut to facilitate the installation clamp The dimensions of the cut are shown below

The final part is shown in the following figure

Transfer the Model to Pro/MECHANICA

From Applications pull-down menu select

From Insert pull-down menu, select

Surface Region

Or click on the Create a Simulation Surface

Region button on the right toolbar

Sketch -> Done Pick the bottom surface of the heat sink as

sketching plane

Select Right under SKET VIEW, and pick RIGHT datum plane as a horizontal or vertical reference for sketching

Make sure to include FRONT datum plane as additional reference

Create two centerlines to ensure the symmetry, then create a square with 0.012 as the sides

Click

When prompted with Select surface or surfaces to be split,

Select surface to add, pick

anywhere on the surface (bottom surface of the heat sink)

OK -> Done -> OK to complete the

surface region creation

Assign Material to the Part

From Properties pull-down menu, select Materials

Or click the Define Material button from the right toolbar

Assign CU as the material of the heat sink

Assign -> Part

Pick the heat sink Click the OK button

Click the Close button

Generate the Elements Using AutoGEM

The model can be autogemmed during the run, or before the run, if materials have been assigned

Select AutoGEM -> Create

Or click the Create p-mesh for

Geometric Element Modeling button

Close

File -> Save Mesh

Close

Assign Boundary Conditions – Convection Condition

Create a convection condition on all surfaces except the bottom

The temperature inside the computer is assumed to be a constant 30 degrees C

Although MKS units are defined, degrees C can be interchanged with degrees K if

this is done consistently for all inputs and outputs Prescribed temperature boundary conditions are generally not used in transient thermal analyses They may conflict

with the initial model temperature

From Insert pull-down menu, select

Enter 100 for Convection Coefficient

h, and 30 for Bulk Temperature

OK

Tip: For easy surface selection choose Box Select then drag a bounding box Hold CTRL and select the surface region (square area) located in the middle bottom surface to deselect it

Place Heat Loads

Place a time varying heat load of 50 watts on the base surface

From the Insert pull-down menu, choose

Heat Load

Select Surface

Or click on New Heat Load on Surface icon in the toolbar

Pick the square surface region on the bottom surface of the heat sink

Enter 50 for Q, and click the Time Dependent radio button as the heat load in the problem varies with time

Select the Function button on the Heat Load definition form The Function Definition dialog box appears

Under Description, enter the following text:

CPU heats up and reaches maximum output of 50 W at 150 seconds

Under Type change to Table

Click on Add Row button

Fill in the dialog box as shown below

Click OK

Enter the time, and value as shown on the figure on the left

The value in the right hand column is set to after 150 seconds This

A graph of the function can be seen by selecting Review

Click the Graph button

Create a Transient Thermal Analysis

Create a transient thermal analysis with Single-Pass Adaptive convergence method For some runs, the Quick Check convergence method may be used to get a quick reading of the model Specify 22 C for uniform initial temperature Typically the estimated variation is left set to Auto In this case the user estimates the heat sink will start at 22 C and reach a maximum of about 52 C so a value is input This preliminary knowledge is most useful when Automatic output intervals are used Tip:

Analysis -> Mechanica Analyses/Studies…

Or click on Run a Design Study in the top toolbar

From File pull down menu, select

New Transient Thermal

Under Name, type in

Transient_Analysis

Under Description, type in the following:

Determine the temperature of the CPU heat sink during the first

1000 seconds after the computer is booted

Click on BndyCondSet1 to highlight it Both

BndyCondSet1 and ThermLoadSet1 are

highlighted

Enter 22 for the initial

Temperature

Keep the rests default

Click on Convergence tab, and make sure Single-Pass

Adaptive method is selected

Click on Output tab

Under Output Intervals, select

User-defined Output Intervals

Change the

Plotting Grid to 4

Change the Number of Master

Intervals to 40

Click on User Defined Steps

button

Click on to unchecked all

Drag the scroll toolbar

to the last interval number 40

Enter 1000 seconds for number 40

Check on Full results

at row number 40 Click on

OK

Run the Transient Thermal Analysis

Run the analysis by clicking

Close the window Close the Analyses and Design Studies

dialog box

Review the Results

Click on icon

Enter Window Name

as “temp” for temperature distribution

Enter Title “

Temperature Distribution of Heat Sink”

Under Design Study and Analysis, make sure that

Click Display Click this icon

Make sure you fill in the following form (window) as shown below:

Check on Continuous Tone

Click the OK and Show button

Click on

Enter the Name of

max_dyn_temp

Type in the Title of Graph of

Max Dynamic Temp

Under Display type, select

Graph

Select Measure in the

Quantity box

Click on

File -> Exit Results

Click on Yes button

Type in File Name: transient for the results to be saved

Click the Close button

Save the model

Steady State Thermal Analysis

Expand the Loads/Constraints in the

Model Tree until you see HeatLoad1

Left-click HeatLoad1, then right-click it

Select Edit Definition

Uncheck Time Dependent option, and click OK -> Done

Create a Steady State Thermal Analysis

From Analysis pull-down menu, select Mechanica Analyses/Studies

From File pull down menu, select

New Steady State Thermal

Name the analysis as

Steady_State

Convergence Method: Multi-Pass Adaptive

Set the Maximum

Polynomial Order to

9

Convergence: Local

Temperatures and Local Energy Norms 5

%

OK

With the Name Steady_State highlighted, run the analysis by clicking

Click Yes

When the run is completed without error

Close the window

Close the Analyses and Design Studies dialog box

Review the results

Click

Enter Window Name as

“temp_steady” for temperature distribution Enter Title “ Steady State

Temperature Fringe Plot

of Heat Sink”

Make sure you fill in the following form (window) as shown below:

Click Display Options

Check on Continuous Tone Check on Show Element

Create a Capping Surface Display

Turn off Show Element Edges, and display the heat sink in default

orientation

Insert -> Cutting/Capping Surfs…

Under Type, select Capping Surface

OK

To delete Capping Surface display, select

Edit -> Delete Capping Surface

Create a Maximum Temperature Convergence Graph

Click on to copy the definition Fill in the Result Window Definition dialog box

as shown below

Click on OK button Display the maximum temperature convergence graph by

selecting View -> Display, and select conv

Click on to copy the definition Fill in the Result Window Definition dialog box as shown below

Click on OK button Display the maximum temperature convergence graph by

selecting View -> Display, and select flux

Save the all result windows -> and also Save the model before exiting

Pro/ENGINEER