Carnegie Mellon

Mechanical Engineering

Self-paced learning on the Web
FEM/ANSYS

 

T3 Transient Slab
Home Course Info Problems Test Problems Students Reference

Thermal #3: Transient heat transfer analysis of a rectangular slab

 

Introduction: In this example you will model a transient heat transfer. We will see how the temperature field changes over time.

Physical Problem: We will model a rectangular slab with a hole in its center. It is maintained at a constant temperature at one end and there is convective heat transfer at the other end. The top and bottom of the slab are insulated.

Problem Description:

 

bullet

The slab is made of material with density 5000 kg/m3. Its specific heat is 200 J/Kg K, and thermal conductivity is 5 W/m K.

bullet

The bulk temperature on the right of the slab is 293K, and the Film Coefficient is 100 W/m2K.

bullet

On the left side the temperature on the boundary is 773K.

bullet

Units: Use S.I. units ONLY

bullet

Geometry: The hole in the center has a radius of 1cm. The hole is located at the center of the slab. See figure for the rest of the dimensions.

bullet

Boundary conditions: There is convection along the side walls. The top and the bottom walls are insulated. The initial temperature of the slab is 293K throughout.

bullet

Objective:
bullet

To plot the temperature field in the slab 50 seconds after the boundary conditions have been suddenly applied to the slab.

bullet

To animate the temperature field to see how it develops as time elapses.

bullet

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

bullet

Figure:

 

 

bullet

IMPORTANT: Convert all dimensions and forces into SI units.

 

STARTING ANSYS   

 

bullet

Click on ANSYS 6.1 in the programs menu.

bullet

Select Interactive.

bullet

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.

bullet

Click on Run.

 

 

MODELING THE STRUCTURE

 

bullet

Go to the ANSYS Utility Menu.
bullet

Click Workplane>WP Settings.

bullet

The following window comes up:

 

 

bullet

Check the Cartesian and Grid Only buttons

bullet

Enter the values shown in the figure above.

bullet

Go to the ANSYS Main Menu and click Preprocessor>Modeling>Create>Area>Rectangle>By 2 Corners

bullet

The following window comes up:

 

 

 

 

bullet

Now we will pick the end points of the rectangles.

bullet

First make the outer rectangle of dimensions 15 cm X 5 cm (30 X 10 units on the grid).

bullet

Now got to Preprocessor>Modeling>Create>Area>Circle>Solid Circle. Create a circle of radius 1cm and with center at the center of the rectangle.

bullet

Now go to Preprocessor>Modeling>Operate>Booleans>Subtract>Areas, and subtract the circle from the rectangle by choosing the rectangle first, then the circle.

bullet

If you cannot see the complete workplane then go to Utility Menu>Plot Controls>Pan Zoom Rotate and zoom out to see the entire workplane.

bullet

The model should look like the one below:

 

 

MATERIAL PROPERTIES

 

bullet

We need to define material properties separately for steel, and the insulation material.   

bullet

Go to the ANSYS Main Menu and click Preprocessor>Material Props>Material Models.  In the window that comes up choose Density. Put in 5000 for density.  From the same window choose Thermal>Specific Heat and enter 200.  From the same window choose Thermal>Conductivity>Isotropic and enter 5 for the thermal conductivity.  The following windows will appear as follows:

 

 

 

 

bullet

Fill in the appropriate values as shown in the figure above. Click OK.

bullet

Now the material 1 has the properties defined in the above table. This represents the material of the slab.

 

ELEMENT PROPERTIES

 

bullet

SELECTING ELEMENT TYPE:

bullet

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

 

 

bullet

Type 1 in the Element type reference number.

bullet

Click on Thermal Solid and select Quad 8node 77. Click OK. Close the 'Element types' window.

bullet

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:

 

bullet

DIVIDING THE WALL INTO ELEMENTS:

bullet

Go to Preprocessor>Meshing>Size Controls>Manual Size>Lines>All Lines. In the menu that comes up type 0.005 in the field for 'Element edge length'.

 

 

bullet

Click on OK. Now when you mesh the figure ANSYS will automatically create a mesh, whose elements have a edge length of 0.005m along the lines you selected.

bullet

Now go to Preprocessor>Meshing>Mesh>Areas>Free. Pick the slab area and click OK. The meshed slab look like the following:

 

 

BOUNDARY CONDITIONS AND CONSTRAINTS

 

bullet

Go to  Preprocessor>Loads>Define Load>Apply>Thermal>Convection>On Lines. Pick the right line along the outer boundary. Click OK. The following window comes up.

 

 

bullet

Enter 100 for "Film Coefficient" and 293 for "Bulk Temperature" and click OK.

bullet

Go to Preprocessor>Loads>Define Load>Apply>Thermal>Temperature>On Lines. Pick the left line along the outer boundary. The following window comes up.

 

 

bullet

Enter the value of the boundary temperature on the left edge of 773 K.

bullet

Now the Modeling of the problem is done.

 

SOLUTION

 

bullet

Go to ANSYS Main Menu>Solution>Analysis Type>New Analysis.

bullet

Select Transient"and click on OK, then select Full in the window that comes up.

bullet

Go to Main Menu>Solution>Load Step Opts>Time/Frequency>Time-Time Step.

bullet

The following window comes up:

 

 

bullet

Fill in the values as shown and click OK.

bullet

Now click Solution>Load Step Options>Output Controls>Solution Printout.

bullet

The following window comes up. Enter the values as shown and click OK.

 

 

bullet

Now click Solution>Load Step Options>Output Controls>DB/Results File.

bullet

The following window comes up. Enter the values as shown and click OK.

 

 

bullet

Now go to Solution>Define Loads>Settings>Reference Temp.

bullet

The following window comes up. Fill in the values shown and click OK.

 

 

bullet

Go to Solution>Define Loads>Apply>Thermal>Temperature>Uniform Temperature.

bullet

The following window comes up. Enter the values as shown and click OK.

 

 

bullet

Now go to Solution>Solve>Current LS.

bullet

Wait for the solution to get done.

bullet

Close the "Stat Command" window.

bullet

Now the solution is done.

 

POST-PROCESSING

 

bullet

Plotting the temperature field after 50 secs.

bullet

Go to ANSYS Main Menu and click on General Postprocessing>Read Results>By Load Step. The following window will come up.

 

 

bullet

Enter values as shown and click OK.

bullet

Now go to General Postprocessing>Plot Results>Contour Plot>Nodal Solution.

bullet

The following window comes up. Enter the values as shown and click OK.

 

 

bullet

The temperature distribution looks something like the plot below.

 

 

bullet

Animating the development of the temperature field

bullet

Go to Utility Menu>Plot Controls>Animate>Over Time. The following window comes up. Enter the values as shown and click OK:

 

 

bullet

Click below to take a look at the animation.

bullet

Temperature field animation

 

 

Home Course Info Problems Test Problems Students Reference
Send mail to the Teaching Staff with questions or comments about this web site.