Tutorial 1: Fin

Introduction: In this example you will learn to model a cooling fin for electronics. This involves heat generation, conduction and convection.

Physical Problem: All electronic components generate heat during the course of their operation. To ensure optimal working of the component, the generated heat needs to be removed and thus the electronic component be cooled. This is done by attaching fins to the device which aid in rapid heat removal to the surroundings.

Problem Description:

The problem is an introduction to the upcoming tutorials 5 and 6.

The fins are made of aluminum with thermal conductivity of 180 W/m K.

Units: Use S.I. units … centimeters ONLY

Geometry: See figure.

Boundary conditions: There is a uniform heat source along the top boundary of the fin assembly. ( T=100^oC ) The bottom of the fin allows for heat transfer. Within the fin there is uniform heat generation. The rest of the fin is insulated. The Film Coefficient is 50 W/m²K and the Bulk (ambient) Temperature is 20^oC. For now, the value for the heat generation within the fin is set to 1 x 10⁵.

Objective:

To determine the nodal temperature distribution.

To determine the maximum value of temperature in the component.

You are required to hand in print outs for the above.

Figure:

This is the assembly of the entire fin… analyze only the section of the light blue

fins that does not include the base…

Front View

IMPORTANT: Convert all dimensions and forces into SI units.

Basic Outline of the Problem:

Preprocessing:

1. Start ANSYS.

2. Create areas.

3. Define the material properties.

4. Define element type. (Quad 8node 77 element, which is a 2-D element for heat transfer analysis.)

5. Specify meshing controls / Mesh the areas to create nodes and elements.

Solution:

6. Specify boundary conditions.

7. Solve.

Postprocessing:

8. List the results of the temperature distribution.

9. Plot the results of the temperature distribution.

Exit:

10. Exit the ANSYS program, saving all data.

STARTING ANSYS

Click on ANSYS 6.1in the programs menu.

Select Interactive.

The following menu that comes up. Enter the working directory. All your files will be stored in this directory. Also enter 64 for Total Workspace and 32 for Database.

Click on Run.

MODELING THE STRUCTURE

Go to the ANSYS Utility Menu.

Click Workplane>WP Settings.

The following window comes up

	Check the Cartesian and Grid Only buttons.
	Enter the values shown in the figure above.
	Select Workplane>Display Working Plane
	Now use Utility Menu>Plot Controls>Pan Zoom Rotate and use the following window to select ISO mode and translate and zoom the working plane to an appropriate viewing distance.

	Go to the ANSYS Main Menu Preprocessor>Modeling>Create>Areas>Rectangle>By 2Corners.
	The following window comes up:

	Enter the values as shown and click OK.
	The modeling is now finished.

MATERIAL PROPERTIES

	We need to define material properties for aluminum.
	Go to the ANSYS Main Menu
	Click Preprocessor>Material Props>Material Models. In the window that comes up choose Thermal>Conductivity>Isotropic.

Enter 1 for the Material Property Number and click OK. The following window comes up.

	Fill in 180 for Thermal conductivity. Click OK.
	Now the material 1 has the properties defined in the above table. This represents the material properties for aluminum (k=180). Once finished, exit the material model window.

ELEMENT PROPERTIES

	SELECTING ELEMENT TYPE:
	Click Preprocessor>Element Type>Add/Edit/Delete... In the 'Element Types' window that opens click on Add... The following window opens.

	Type 1 in the Element type reference number.
	Click on Thermal Mass Solid and select Quad 8node 77. Click OK. Close the 'Element types' window.
	So now we have selected Element type 1 to be a thermal solid 8node element. The component will now be modeled with thermal solid 8node elements. This finishes the selection of element type.

MESHING

	DIVIDING THE TOWER INTO ELEMENTS:
	Go to Preprocessor>Meshing>Size Controls>Manual Size>Global>Size. In the menu that comes up type 0.00025 in the field for 'Element edge length'.

	Click on OK. Now when you mesh the figure ANSYS will automatically create meshes that have an edge length of 0.00025m along the objects you selected.
	First we will mesh the steel area. Go to Preprocessor>Meshing>Mesh Attributes>Default Attributes. Make sure the window indicates "Material Ref.#1". The window is shown below.

Now go to Preprocessor>Meshing>Mesh>Areas>Free. Pick the area and click OK.

BOUNDARY CONDITIONS AND CONSTRAINTS

	Go to Preprocessor>Loads>Define Loads>Apply>Thermal>Heat Generate>On Areas.
	Select the rectangular area and Click OK.
	The following window comes up. Enter this datum.

	Next, we apply the convective boundary conditions.
	Go to Preprocessor>Loads>Define Loads>Apply>Thermal>Temperature>On Lines.
	For the top of the fin … apply the following value:

Repeat the process of setting a temperature boundary condition on the line defining the bottom of the fin. Set this temperature to 100°C.

Now the Modeling of the problem is done.

SOLUTION

	Go to ANSYS Main Menu>Solution>Analysis Type>New Analysis.
	Select Steady State and click on OK.
	Go to Solution>Solve>Current LS.
	An error window may appear. Click OK on that window and ignore it.
	Wait for ANSYS to solve the problem.
	Click on OK and close the 'Information' window.

POST-PROCESSING

	Listing the results.
	Go to ANSYS Main Menu General Postprocessing>List Results>Nodal Solution. The following window will come up.

Select DOF solution and Temperature. Click on OK. The nodal displacements will be listed as follows.

You will find the maximum value of temperature at the end of the above table.

MODIFICATION

	You can also plot the displacements and stress.
	Go to General Postprocessing>Plot Results>Contour Plot>Nodal Solution. The following window will come up:

Select DOF solution and Temperature to be plotted and click OK. The output will be like this: (playing with Pan Zoom Rotate)

Saving Projects

· Simply go to Utility Menu>File>Save As… and save the project using the desired filename. To open the file later, run Interactive (the first thing explained in this tutorial) as usual, and when that is done, go to Utility Menu>File>Resume From… and choose the saved job from the directory it is saved in.