The following sample problem was designed to familiarize you with the basics of solving heat transfer problems using WinTherm. This is just one possible solution path for solving the problem. As you become more familiar with WinTherm, you will develop your own methods for solving problems such as this.

11.6.1 Model Description

Pipe: 10 x 1 inches Duct: 10 x 2 x 2 inches Top of Box to Bottom of Pipe: 0.5 inches

Objectives

• To create basic geometry using Geometry Primitives
• To become familiar with the following Geometry Operations: Scale, Translate, Rotate, Copy, Condense, Delete & Check Distance
• Connecting and Unconnecting Conduction between Parts

Start up WinTherm by double clicking the WinTherm icon.

11.6.2 Create Plate Primitive

Select the Geometry Tab to create the duct and cylinder geometry.

The duct geometry can be modeled using Plate Primitives. Under the Create Sub-Tab select the Plate Primitive.

From the main menu select Options -> Units -> English to switch from SI to English units if necessary.

Enter the Plate Dimensions: Length = 10 inches and Width = 2 inches.

Enter the Number of Elements along both the Length and Width: Length = 20 and Width = 5.

Press the Create button and the plate geometry will appear.

To create the rest of the duct, you will need to translate and rotate copies of the plate primitive that you just created.

Create the top of the duct.   Select the Edit Sub-Tab.  Select Copy as the Operation.  Under Copy Parameters enter 2 inches as the Z Translation Vector.  Click the Copy Button at the bottom of the Edit page. 

Create the right side of the duct.  If not already selected, select the bottom of the duct by clicking on it.  The part will appear green in color when selected as opposed to gray.  (Note: From the Main Menu select View -> Legend for information on graphics colors.)   Select Copy as the Operation.  Under Copy Parameters enter 0 inches for all Translation Vectors. Click the Copy Button at the bottom of the Edit page.

The new part will be copied directly on top of the original part.  Increase the part number to 3 in the Part Selector Number duct at the top of the Geometry page to select the new part.

Select Rotate as the Operation.  Under Rotation Parameters enter a Rotation Angle of 90 degrees.   The rotation point should be 0, 0, 0.  Select X as the rotation axis.  (Note: Use the XYZ World Coordinate Icon located at the bottom of the graphics window as a reference when manipulating geometry.)   Click the Rotate button at the bottom of the page.

Note: If you make a mistake, select the part, under Operations select Delete, and then click the Delete button at the bottom of the edit page.

Create the left side of the duct.  Select the bottom of the duct by clicking on it.  Select Copy as the Operation.  Under Copy Parameters enter 0 inches for all Translation Vectors. Click the Copy Button at the bottom of the Edit page.

As with the right side, the new part will be copied directly on top of the original part.  Increase the part number to 4 in the Part Selector Number duct at the top of the Geometry page to select the new part.

Select Rotate as the Operation.  Under Rotation Parameters enter a Rotation Angle of -90 degrees.   The rotation point should be changed to  0, 2, 0.   Select X as the rotation axis. Click the Rotate button at the bottom of the page.

Reverse Normals. The normals of the bottom of the duct are facing in instead of out.  Select the bottom of the duct by clicking on it.  From the main menu select Tools -> Reverse Normals.  All the sides of the duct should now be facing out (light green on the outside, dark green on the inside).

Check Distance. Select the Diagnostics Sub-Tab.  Change the selection mode to Select Element by clicking the Element button on the toolbar.   Select the middle element at the front of the top of the duct by clicking on it as the First Element.  Select the middle element at the front of the bottom of the duct by clicking on it as the Second Element. 

A pink line will connect the two elements, and the distance between the two elements will be displayed in the upper left-hand corner of the Graphics Window.

Try checking the distance between other elements.  When finished, select Clear to remove the Check Distance line.  Change the selection mode back to Select Part by clicking the Part button on the toolbar.

11.6.4 Create and Translate Cylinder Primitive

The pipe geometry can be modeled using a Cylinder Primitive. Under the Create Sub-Tab, select the Cylinder Primitive.

Enter the Plate Dimensions: Length = 10 inches and Diameter = 1 inch.

Enter the Number of Elements along both the Length and Width: Along Length = 20 and Around Diam. = 10.

Press the Create button and the plate geometry will appear.

Translate the Pipe.  Select the pipe by left clicking on it in the Graphics Window.  Select the Edit Sub-Tab.   Select Translate as the Operation.  Under Translation Parameters set the Translation Vector to 0, 1, 3. Click the Translate Button at the bottom of the page.

11.6.5 Set Boundary Conditions and Run Model

You will need to assign a temperature to the pipe.  Select the Editor Tab.  Select the Parts Sub-Tab.  If not already selected, make the pipe the active part by selecting it.   Choose Assigned under the Temperature duct.

Then set the temperature of the pipe to 300F.

The solution parameters are located under the Analyze Tab | Params Sub-Tab.  The Start Time and Duration should be left at the default values 0, with 0 minutes which will solve for the steady-state solution.  Click the Run button to initiate the thermal solution.

The view factors will be calculated first and then the transient solution.  The Thermal Solution with the successfully completed duct will appear when the thermal solution is complete.  Click OK.  Click Auto Scale to change the temperature Display Scale to a more reasonable range.   Notice the temperature of the side of the duct is much cooler than the top of the duct.  The reason for this is the pipe is radiating to the top of the duct, but there is no conduction between the top, bottom and sides of the duct.  The model needs to be condensed.

11.6.6 Condense Parts

The Condense command allows you to reduce two or more vertices into a single vertex. The reason for condensing vertices is that WinTherm will only calculate conduction between parts that share common vertices. Parts that have vertices nearby, penetrating, or even coincident (on top of each other) vertices from another part will NOT have any conduction.

Select the Geometry Tab | Edit Sub-Tab.  Under Operations select Condense.  Set the Max Vertex Separation to 0.001 inches.  Click the Condense button at the bottom of the page.

The following information should appear in the Status Window.

Return to the Analyze Tab | Params Sub-Tab and click the Run button to re-invoke the thermal solution.

Notice the top of the duct now conducts to the sides of the duct.

To break the conduction between the top and sides of the duct, return to the Geometry Tab | Edit Sub-Tab.  Select the top of the duct part.  Select Translate as the Operation.  Under Translation Parameters set the Translation Vector to 0, 0, 3.  Deselect Translate Connected.  This will cause the connection to adjoining parts to be broken and there will no longer be conduction between the parts. (Note: If Translate Connected is selected, the part maintains connections to other parts.  The geometry will be stretched to maintain the connection. Try it.)  Click the Translate Button at the bottom of the page. 

Now change the translation vector to 0,0,-3.  Click the Translate Button to return the duct top back to its original position.

Return to the Analyze Tab | Params Sub-Tab and click the Run button to re-invoke the thermal solution.

Notice conduction has been broken between the top and sides of the duct.  You may use Condense to reconnect the top and sides of the duct.