In this example you will learn to model a composite material and analyze one dimensional conduction properties. Using ANSYS will allow you to output the temperature distribution in an extremely simple and accurate way.
Problem Description:
· We are modeling heat transfer in a block with a gap filled with different gases.
· All units are S.I.
· Boundary Conditions:
1) The left side of the block has a constant temperature of 400 K.
2) The right side of the block has convection (h=20 W/m-K ; T= 300 K)
3) The Al section generates heat at a rate of 200 W/m3
4) The He section absorbs heat at a rate of 175 W/m3
· Material Properties:
Aluminum(1st layer): KAl = 235 W/m*K
Helium(2nd layer): KHe = 0.1513 W/m*K
Copper(3rd layer): KCu = 400 W/m*K
· Dimensions
Length = 3 m
Width = 3 m
Thickness of each Layer = 1 m
· Objective: Find the nodal temperature distribution and the rate of heat loss from the furnace.
· Figure:
Basic Outline of the Problem:
Preprocessing:
1. Start ANSYS.
2. Create areas through keypoints.
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 6.1 in the programs menu.
· Select Interactive.
· The following menu comes up. Enter the working directory. All your files will be stored in this directory. Also under Use Default Memory Model make sure the values 64 for Total Workspace, and 32 forDatabase are entered. To change these values unclick Use Default Memory Model.
· Click RUN
Modeling the Structure:
· Go to the ANSYS Utility Menu (the top bar). Click Workplane>WP Settings…
· The following widow comes up: (notice the numbers are different)
· Check the Cartesian and Grid Only buttons
· Enter the values shown in the figure above. Click OK
· Go to the ANSYS Utility Menu (the top bar). Click Workplane>Display Working Plane. This will display the working grid on the workspace.
· Use Utility Menu>PlotCtrls>Pan Zoom Rotate to display the grid as shown in the next step below.
· Next, go to the ANSYS Main Menu (on the left hand side of the screen) and clickPreprocessor>Modeling>Create>Keypoints>On Working Plane.
· The following window comes up:
· Click on the working plane below to select the points (they follow the dimensions explained in the beginning, (1m x 3m). After setting the workplane settings in the beginning, you should be aware that each line on the plane equals to 1m. When done, click OK.
· Now you have created the points to make the block.
· Now select Preprocessor>Modeling>Create>Areas>Arbitrary>Through KPs. A window will now appear on the left of the screen.
· Select the points that form the 1st section. Click Apply such that it is formed separate from the other two areas.
· Repeat the step of selecting the KPs that make up each area, and clicking Apply until all three layers are defined. (Click OK for the last one)
· The model should look like this now: (note, you have a black background)
Material Properties:
· Now that we have built the model, material properties need to be defined such that ANSYS understands how heat travels through this composite solid.
· Go to the ANSYS Main Menu
· Select Preferences. We will set up the drop menus only to include thermal tasks, to make everything easy to navigate.
· Select Thermal and hit ok. Now you are ready.
· Click Preprocessor>Material Props>Material Models.
· The pop-up window will now look like this:
· In the window that comes up, select Material>New Material
· Hit OK. Repeat the process for the third material. (repeat the last step once more)
· Choose Thermal>Conductivity>Isotropic.
· The following window comes up:
· Fill in 235 for Thermal conductivity. Click OK. This is the Thermal Conductivity of Al.
· Now repeat the steps of clicking Thermal>Conductivity>Isotropic and then defining the Thermal Conductivity as 0.1513 for the Model 2.
· You have now defined the k value of Helium.
· Define the last section and this time use K = 400. This is the Thermal Conductivity of Copper.
· Now exit the “Define Material Model Behavior” Window.
Element Properties:
· Now that we’ve defined what material ANSYS will be analyzing, we have to define how ANSYS should analyze our block.
· 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.
· Now we have selected Element Type 1 to be a Thermal Solid 8node Element.
· This finishes the section defining how the part is to be analyzed.
Meshing:
· This section is responsible for telling ANSYS how to divide the block such that it has enough nodes, or points, to produce accurate results.
· Go to Preprocessor>Meshing>Size Controls>Manual Size>Lines>All Lines. In the menu that comes up type 0.05 in the field for Element edge length and 1 for the Spacing Ratio.
· Click on OK. Now when you mesh the figure ANSYS will automatically create square meshes that have an edge length of 0.05m along the lines you selected.
· Now go to Preprocessor>Meshing>Mesh Attributes>Default Attributes. The window is shown below:
· Make sure that the window matches the one above, click OK, and proceed toPreprocessor>Meshing>Mesh>Areas>Free
· A popup window will appear on the left hand side of the screen. This window allows you to select the area to be meshed.
· Choose the 1st area and then click OK in the pop-up window. This both meshes the area and defines it as Material 1. Material 1 (as you recall from before) was set to Aluminum originally by defining the k value of the material as 235 W/m*K.
· Now return to Preprocessor>Meshing>Mesh Attributes>Default Attributes. This time, selectMaterial Number 2 from the dropdown menu and click OK.
· Once the pop-up window appears, select the middle layer and click OK.
· Repeat this process of defining each layer as a different material for Material 3 and mesh it so that all three layers have been meshed.
· The block should now look like this when you are done meshing: (if you choose fit in the pan zoom rotate dialog)
Boundary Conditions and Constraints:
· Now that we have modeled the block and defined how ANSYS is to analyze the block we will apply the appropriate Boundary Conditions. ANSYS refers to all Boundary Conditions under the Loads category, so remember that when looking for commands within the main menu…
· Go to Preprocessor>Loads>Define Loads>Apply>Thermal (from here one can apply any of the loads, or Boundary Conditions, offered by ANSYS.)
Apply Constant Temperature
· Now we’ll apply the given temperature boundary condition on the right side of the block.
· This time, within the Thermal Load category select Temperature>On Lines.
· A popup window will appear on the left hand side of the screen. This window allows you to select the line you wish the load to be applied to.
· Click the innermost boundary of the block and then OK.
· Enter 400 in the popup window as the set temperature for the left edge of the first section:
Apply Convection
· Now we will apply convection to the right side of the composite block. Select Convection>On Lines
· A popup dialog will appear. Select the correct line and hit OK.
· Enter the appropriate values and hit OK.
Apply Heat Generation and Heat Absorption
· The next step is to add heat generation to the composite block.
· Choose Heat Generat>On Areas
· Enter 200 W/m3 for the generation and the hit ok.
· Repeat this step for the second area but input -175 W/m3 to imply absorption.
· Once that is complete, the block should look like this:
Solution:
· Go to ANSYS Main Menu>Solution>Analysis Type>New Analysis.
· Select Steady State and click on OK.
· Go to Solution>Solve>Current LS.
· Wait for ANSYS to solve the problem.
· Click on OK and close the 'Information' window.
Post-Processing:
· This section is designed so that one can present the results of their analysis in the most appropriate way. This presentation can be in the form of tabulated nodal values, curves, etc.
· Go to the ANSYS Main Menu. Click General Postprocessing>List Results>Nodal Solution. The following window will come up:
·
· Select DOF solution and Temperature. Click on OK. The nodal temperatures will be listed as follows:
· Within this window one can numerically find the maximum and minimum value of the temperature within the block. Note that you may have nodes in different places. Therefore your first displayed temperatures might not be the same as the ones shown above. If you scroll down you should find everything.
Modification / Plotting the Results:
· The last section displayed the numerical results, but some people prefer a plot presentation of the temperatures on the block over the numerical results. This is how you go about doing that…
· First 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:
· This is the Final Solution
· To find extra information on Saving an ANSYS model see the Appendix on the ANSYS tutorial mainpage.
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.
