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ME-430 INTRODUCTION TO COMPUTER AIDED DESIGN
TRANSIENT and STEADY STATE THERMAL ANALYSIS OF
HEATSINK
Pro/ENGINEER and Pro/MECHANICA Wildfire 2.0
Dr. Herli Surjanhata

Background

A steady state thermal analysis calculates effects of constant thermal loads on a
model and is used to determine temperatures, heat flow rates, and the heat fluxes in
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.
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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.

Make a cut with the dimensions shown below. 4
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.
5
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.


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.

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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).


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. 11
Close.
File -> Save Mesh.
Close.
BOTTOM SURFACE.

Enter 100 for Convection Coefficient
h, and 30 for Bulk Temperature.
OK
13 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.

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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.

The value in the right
hand column is set to
after 150 seconds. This
value of 1 is a multiplier
for the Q load of 50
Watts.

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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:
Optionally, a temperature gradient from a previously completed steady state analysis
can be used by setting Initial Temperature Distribution to MEC/T instead of Uniform.
17Analysis -> Mechanica
Analyses/Studies…
Or click on Run a Design Study in the

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.
19Change the
Plotting
Grid to 4.

Change the Number of Master
Intervals to 40.
Click on User Defined Steps
button.

Click on

Click
to check the
analysis status.
When the run is
completed without
error.
Close the window.
Close the Analyses
and Design Studies
dialog box.

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Review the Results Click on
icon.
Enter Window Name
as “temp” for
temperature
distribution. Format -> Result Window…
Enter the setting as shown on the left.

23 24Click on
.

Enter the Name of
max_dyn_temp.

Type in the Title of Graph of
Max Dynamic Temp.

Under Display type, select
Graph.

Click on OK.