icepak v12.0 tut 03

Tutorial 3. Use of Parameterization to Optimize FanLocation

Introduction: The purpose of this tutorial is to demonstrate the following ANSYS Icepakfeatures with the help of a small system level model.

In this tutorial you will learn how to:

Use network blocks as one way of modeling packages. Specify contact resistance using side specifications of a block object. Define a variable as a parameter and solve the parametric trials. Specify fan curves. Use local coordinate systems. Generate summary report for multiple solutions.

Prerequisites: This tutorial assumes that you have little experience with ANSYS Icepak,but that you are generally familiar with the interface. If you are not, please reviewthe sample session in Chapter 1 of the Users Guide and Tutorial 1 of this guide assome of the steps that were discussed in these tutorials will not be repeated here.

Problem Description: The system level model consists of a series of IC chips on aPCB. A fan is used for forced convection cooling of the power dissipating devices.Bonded fin extruded heat sink with 8 fins of thickness 0.008m is attached to the ICchips. Fan flow rate is defined by a non-linear fan curve. The system also consistsof a perforated thin grille. A study is carried out for the optimum location of thefan by using the parameterization feature in ANSYS Icepak.

c ANSYS, Inc. June 2, 2009 3-1

Use of Parameterization to Optimize Fan Location

Figure 3.1: Schematic of the Geometry

Step 1: Create a New Project

1. Start ANSYS Icepak, as described in Section 1.5 of the Users Guide.

When ANSYS Icepak starts, the New/existing panel will open automatically.

2. Click New in the New/existing panel to start a new ANSYS Icepak project.

3. Specify a name for your project (i.e., fan locations) and click Create.

ANSYS Icepak will create a default cabinet with the dimensions 1 m 1 m 1 m,and display the cabinet in the graphics window. This cabinet will be modified in thenext section.

Step 2: Build the Model

1. Resize the default cabinet.

The cabinet forms the boundary of your computational model. Press Shift-I fora 3D view. Select Cabinet in the Model manager window and enter the locationvalues as shown in the panel below. The geometry editing panel can be found inthe lower right hand corner of the GUI.

3-2 c ANSYS, Inc. June 2, 2009


Extra: The previous tutorial showed you how to enter these values in the Cabinetpanel.

2. Create the Fan

Click on the Create fans icon ( ) in the object toolbar next to the model treeto create a 2D, intake circular fan on one side of the cabinet. Change the defaultplane to plane YZ. Enter the location values as shown in the geometry panel below:

Defining a parameter for multiple trialOne of the objectives of this exercise is to parameterize the location of thefan. To do this, click Apply after entering in the fan location values. ANSYSIcepak will then ask you for an initial value of zc, enter an initial value of0.1, and click Done.

Figure 3.2: The Param value Panel

We will now set the physical properties which will define the fan behavior:

Now edit the fan object and go to Properties tab.



In the Properties tab, retain the selection of Intake for Fan type and selectNon-linear in the Fan flow group box.

Enter the characteristic curve by clicking on the Edit button and selecting TextEditor in the drop-down list next to Non-linear.

Figure 3.3: The Fans Panel (Properties Tab)

First change the units of the volume flow rate and pressure according to theunits in Table 3.1 and enter the values in pairs with a space between them inthe Curve specification panel.

Table 3.1: Values for the Curve Specification Panel

Volume Flow (CFM) Pressure (in water)0 0.4220 0.2840 0.260 0.1480 0.0490 0.0



Click Accept to close the form. Now, select the Edit button in the Properties tab panel and click on Graph

Editor in the drop-down list next to Non-linear to view the fan curve defined(Figure 3.4).

Figure 3.4: The Fan Curve Panel

In the Properties tab, give the fan an RPM of 4000 in the Swirl group box,located near the upper-right corner of the Properties window of the Fan object.

Enter 2000 for the Operating RPM value in the Options group box.The fan curve defined originally for RPM=4000 will be automatically scaledaccording to the fan laws for the new operating RPM=2000. The swirl RPM(4000)can also be used to compute the swirl factor.

Click Update and Done to close the fan window.Now the model looks as shown in Figure 3.5.

Extra: The fan object has been shaded using shading under the Geometry tab.



Figure 3.5: Model with Fan

3. Set up a Grille.

Click on the Create grille icon ( ) for creating a new grille, set its plane toy-z. Then, using the morph faces icon ( ) move the grille to the max-Xface of the cabinet or resize the grille as shown in the panel:

We will now define properties for the grill by clicking the Properties tab.This is a 50% open perforated thin grille.

Under velocity loss coefficient, retain the default selection of Automatic.

Specify a Free area ratio of 0.5.

Retain Perforated thin vent for the Resistance type.

For more details on loss coefficient data, please refer to Handbook of HydraulicResistance, by Idelchick, I. E.

The model looks as shown in Figure 3.6.



Figure 3.6: Model with Fan and Grill

4. Set up a wall.

The model includes a 0.01 m thick PCB that touches and covers the entire min-Yfloor of the cabinet. The PCB is exposed to the outside with a known heat flux of20 W/m2. In order to take in consideration the heat flux, we will use a wall objectto simulate the PCB.

Click on the Create walls icon ( ) to create a new wall. We will define thegeometry and physical parameters for the wall object:

Make the plane xz.

Use the morph faces icon ( ) from the model toolbar so that the wallobject covers the entire min-Y floor of the cabinet.

Edit the Wall object and go to Properties tab. Give a Wall thickness of0.01m. Set the Solid material to FR-4.

Specify an Outside heat flux of 20 W/m2.

After creating the wall, the model looks as shown in Figure 3.7.



Figure 3.7: Model with Wall Added

5. Create blocks.

In this step, we will create several types of blocks to represent different physics.

Creation of Solid BlocksNow, we will create four blocks that dissipate 5 W each and have a contact

resistance of 0.005 C/W on their bottom faces. Create a new block ( ), and retain the type as Solid and geometry as Prism. Size it as shown in thepanel below:

Edit the block and specify the following in the Properties tab: In the Surface specification group box, click on the Individual sides checkbox

and click Edit (Figure 3.8).



For the Min Y face, toggle on Thermal properties and Additional resis-tance.

Select Thermal resistance from pull down menu next to Additional re-sistance.

Ensure Fixed heat is enabled and set Total power to 0. Set Thermal resistance to 0.005 C/W and click Accept.

Figure 3.8: The Individual side specification

In the Thermal specification group box, retain the selection of default forSolid Material (you can also select Al-Extruded which is the default).

Set Total Power to 5 W.

Click Done to close the panel.



Next, make three copies of this block with an X offset of 0.08 m.Extra: The previous tutorial showed you how to make a copy of an object.

Figure 3.9: Creation of Solid Blocks

Creation of Network blocksLet us now create four IC chips in the form of network blocks. To createa network block, we will create a Block object and change the block typeto Network in the Properties tab. Each network block will have junction-to-board, junction-to-case, and junction-to-sides thermal resistances. The valuesof these resistances are known a priori.

Add a new block, and position it as shown in the panel below:

Edit the block to change the properties of this block;

Ensure that the Block type is set to Network.

Toggle on Star Network.

Enter the following parameters: Board side = Min Y, Rjc = 5 C/W,Rjc-sides = 5 C/W, Rjb = 5 C/W, and Junction power = 10 W.



Figure 3.10: The Properties Panel



Now make three copies of this network block with an X offset of 0.08 m. Thisfinishes the creation of the network blocks.

Creation of a Hollow BlockFinally, to cut out a section of the cabinet from the computational domain, wecan create a hollow block. This represents a region that does not affect heattransfer, but alters the flow patterns.

Create a new Block, make sure it is a hollow.

In the Geometry tab, create a new Local coord system. Select Create newfrom the Local coord system: drop-down list. Enter X offset = 0.1, Y offset= 0, Z offset = 0. Click Accept. This is just to demonstrate the use oflocal coordinate system.

Further, size the block as follows:

6. Create Heatsink.

Now we will create the detailed heat sink. The heat sink base acts as a heat spreaderfor all the chips.

Click on the Create heat sinks icon ( ) and edit it, enter its location and propertiesas shown in the following table:



Table 3.2: Heatsink Properties

GeometryPlane: x-z, xS = 0.05, yS = 0.03, zS = 0.1, xE = 0.34, zE = 0.23Base height: 0.01 mOverall height: 0.06m

PropertiesType: DetailedFlow Direction: XDetailed Fin type: Bonded finFin spec: by Count/thickFin Count: 8Thickness: 0.008mFin material: defaultBase material: Cu-PureFin bonding Edit button (lower-right corner)Effective thickness: 0.0002mSolid material: default



Click Update and Done. This completes the model building process. The completemodel should look like that shown in Figure 3.11.

Figure 3.11: Final Model

Step 3: Creating separately meshed assembliesOne of the key aspects of modeling is to use an adequate mesh for the model. We needto have a fine mesh in the areas where temperature gradients are high or flow is turning.Having a too coarse of a mesh will not give you accurate results and at the same time, toofine a mesh may lead to longer run times. The best option is to explore the model carefullyand look for opportunities to reduce mesh counts in the areas where the gradients arenot steep. Creating non-conformal assemblies gives required accuracy along with reducedmesh count. Select set of objects to create assemblies. Also decide suitable slack valuesfor assembly bounding box. Your selection can be reviewed in the section below where wewill create non-conformal meshed assemblies.

We will now create two non-conformal meshed assemblies.

To create the first assembly, first highlight all the blocks (except the hollow block) and theheat sink object in the model tree, then right-click on them and choose Create assembly.Then, right mouse click and select Rename from the menu. Rename the assembly, asHeatsink-packages-asy. To build the bounding box for the assembly called Heatsink-packages-asy, double-click on it to edit the assembly.



In the Meshing tab of the Assemblies panel, toggle on Mesh separately, and then set theSlack parameters as the following:

Table 3.3: Slack Values for Heatsink-packages-asy Assembly

Min X 0.005 m Max X 0.015 mMin Y 0.005 m Max Y 0.005 mMin Z 0.005 m Max Z 0.005 m

To create a non-conformal mesh interface, it is necessary to use a positive slack value,unless the bounding box touches the cabinet or a hollow block is used, in which case azero slack value would be acceptable.

Note that for the Heatsink-packages-asy, we have set a bounding box that is 0.005 m biggerthan the assembly at five sides except Max X where the slack is defined higher (0.015 m)to capture the wake region of the flow.

Click Update and Done to complete the bounding box specifications for the assembly.

Following the same procedure above, create one more assembly for the fan object (nameit Fan-asy). Use the following table to assign the Slack values for the Fan-asy assembly.

Table 3.4: Slack Values for Fan-asy Assembly

Min X 0 m Max X 0.005 mMin Y 0.002 m Max Y 0.002 mMin Z 0.002 m Max Z 0.002 m

Step 4: Generate a MeshNow, open the Mesh control panel, keep the default values for the mesh settings andensure that Mesh assemblies separately is on. Then click Generate mesh. You may get awarning about minimum separation. Click on Change value and mesh.

Extra: This warning appears because the Minimum gap (separation) which is like a toler-ance setting for the mesher is larger than 10% of the smallest feature in the model.When there are objects smaller than the mesher tolerance, those objects will not bemeshed correctly. To avoid this we use the change value and mesh option whichmodifies the minimum gap to 10% of the smallest object. This option is used for thisparticular tutorial and may not be applicable all the time. As separation setting is



a useful tool designed to avoid unnecessary mesh due to inadvertent misalignmentsin the model (without modifying the geometry), we may use other options suitableto the model. Please refer to the Periodic Boundary Conditions: Determining HeatSink Performance Tutorial located on the FLUENT User Services Center websitefor more details.

Examine the mesh by taking plane cuts; examine Face alignment and Quality ratio. Goto the Mesh control panel, click on the Display and Quality tabs for examining the mesh.

Step 5: Setting up the Multiple TrialsBefore we start solving the model, we will set up the parametric trials for the fan locationparameter zc.

Go to the Solve menu and select Define trials. The Parameters and optimization panel pops up.

Toggle on Parametric trials in the Setup tab.

Select the Design variables tab and next to Discrete values, type 0.165 following0.1, separated by a space as shown in the Figure 3.12:

Click Apply.



Figure 3.12: The Parameters and optimization



After the first trial has been completed, ANSYS Icepak has the options of startingthe following trial(s) from the default initial conditions specified in Problem setuppanel, or from the solution(s) of the trial run(s) that have completed.

For this model, next go to the Trials tab and ensure the Restart ID is blank for the2nd trial. This instructs ANSYS Icepak to start the 2nd run from the default initialconditions.

Click on Reset button and select Values to use the base names for trial naming. Click Done to close the Parameters and optimization panel.

Step 6: Creating monitor PointsCreate two monitor points by dragging and dropping (block.1 and grille.1) into the Pointsfolder to monitor the velocity in the grille and the temperature in one of the solid blocks.The variables to be monitored can be easily changed by selecting them in the Monitorpoints panel.

Figure 3.13: The Modify point Panel



Step 7: Physical and Numerical SettingSet the overall problem definition to turn on the energy and turbulence using Zero equa-tion model. Since we are not solving for natural convection, there is no need to turn onthe Gravity vector.

Problem setup Basic parameters

Figure 3.14: The Basic parameters Panel



Solution settings Basic settingsEnter 200 in the Number of iterations field in the Basic settings panel.

Extra: You can check Reynolds and Peclet numbers by clicking Reset button.

Figure 3.15: The Basic settings Panel

Step 8: Save the ModelANSYS Icepak will save the model for you automatically before it starts the calculation,but it is a good idea to save the model (including the mesh) yourself as well. If you exitANSYS Icepak before you start the calculation, you will be able to open the job you savedand continue your analysis in a future ANSYS Icepak session. (If you start the calculationin the current ANSYS Icepak session, ANSYS Icepak will simply overwrite your job filewhen it saves the model.)

FileSave projectAlternatively, click the save button ( ) in the file commands toolbar.



Step 9: Calculate a SolutionSelect the Solve menu and click on Run solution. In the Solve panel, toggle on Performmultiple trials and Write overview of results when finished, and then click Start solution.

Figure 3.16: The Solve Panel



Step 10: Examine the ResultsOnce the solutions are done, click on the Post menu and select Load solution ID. Selectthe solution that corresponds to the first (parametric) run, i.e., c = 0.1. Use the variouspostprocessing features available in ANSYS Icepak to display your solution. In particular,use:

Plane cut to display the velocity vectors on a plane through the cabinet,

Figure 3.17: Trial 1 Vector Plots at Constant Z Plane Cut

i To view the 2nd parametric run, click on the Post menu and select Loadsolution ID. Select the solution that corresponds to the second parametric run,i.e., c = 0.165. The graphics display window will update automatically.

Object face to display temperature contours on wall.1 and on all blocks, Object face to display temperature contours on the faces of the PCB (wall.1) and

on all blocks

Surface probe to display the temperature values at a particular point,Examine the solution sets of both runs. You will find that, in the second run, themaximum temperature is lower than in the first run and that the network blocksare the hottest objects inside the cabinet. The second trial has the fan located atzC= 0.165 which is closer to the heat sink location. This increases the flow velocityover the heat sinks and thus increases the convective heat transfer coefficient, whichleads to more heat transfer from the fins (blocks) and thus reduces the maximumtemperature.



Figure 3.18: Trial 2 Vector Plots at Constant Z Plane Cut

Figure 3.19: Trial 1 Temperature Contours on Blocks and PCB (wall.1)



Figure 3.20: Trial 2 Temperature Contours on Blocks and PCB (wall.1)

Step 11: Reports

1. Overview Report

At the end of the runs, ANSYS Icepak will automatically display an overview reportsince you toggled on Write overview of results when finished in the Solve panel. Thisreport will have:

fan operating point volume flow rate through the grille heat flow from the chips network junction temperatures heat flows for the wall and the grille

Examine these results. Simply go to the Report menu and then select Solutionoverview and click on View to display the desired overview report.

2. Summary Report

You can also create a single summary report containing the results of all the trialruns completed. Go to the Solve menu and select Define report. In the Definesummary report panel, under Solution ID, select Multiple. The default Filter, * ,picks all the available solution IDs. Create a summary report on a few blocks andverify that the second trial gives lower temperatures.



Step 12: SummaryIn this tutorial, you learned how to set up and solve parametric trials, specify fan curvesand create a new local coordinate system. The use of network blocks to model packageshas been demonstrated and how to specify contact resistance using side specifications ofa block object. A summary report is generated for multiple solutions.

Step 13: Additional Exercise to Model Higher Altitude EffectThe final model can be also used to model the higher altitude affect. In order to modelthis correctly, new air properties at, lets say, 3000m need to be defined and assigned tothe default fluid. The density of air is the most affected property and gets lower as yougo higher in altitude. The data for air properties at a different altitude is presented inmany handbooks and may even include temperature change affect with it. For 3000m wecan select the available library material Air@3000m. Please note that a custom materialhaving any properties can be created and stored in the material library to use in anyproject.



Then, select Problem setupBasic Parameters and assign the new air material to thedefault fluid.

In addition, in the Fan flow section of the Fans Properties tab, all the defined fan curvesneed to be modified by multiplying the existing data with the ratio of densities (thedensity of air at 3000m / the density of air at 0 m) which is smaller than 1. Finally, themodel is ready to be run to account for the effects of higher altitude.


3 Use of Parameterization to Optimize Fan Location

icepak v12.0 tut 03

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