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How to Prepare the Fluid Region for Conjugate Heat Transfer Simulations?

For simulations involving conjugate heat transfer (CHT) analysis, the requirements for the simulation domain are slightly different from the normal procedure where we create a flow volume covering the negative of our overflowed geometry which represents the physical walls. This article describes how to proceed with CHT simulations ensuring the flow domain is accurately created.


Create Flow Volume and Keep Existing Parts

CHT simulation involves heat transfer through both solids and fluid. Hence, we need to keep the original solid parts while extracting the fluid volume as they participate in the heat transfer too. Usually, the CAD model only involves the solid parts, as you can see in the following electronics box example.

an electronics box that will be used in a cht analysis
Figure 1: The original CAD model of the electronics box, which will be used in a CHT analysis

We will use the Flow volume extraction feature under the CAD mode to generate the fluid region needed for CHT analysis. Simply, click on ‘Edit in CAD mode‘ icon.

accessing cad mode feature of simscale
Figure 2: Accessing the CAD mode feature is easy. Just select your CAD model, then click on the Edit in CAD mode icon next to your geometry.

In this example, we will generate the fluid volume inside the electronics box, which has multiple openings. Therefore, we need to use Internal Flow Volume mode. Visit the flow volume extraction article to learn more about the flow volume feature. Extract the flow volume as follows:

  1. Under Flow Volume, select ‘Internal‘.
  2. Click on ‘Seed face‘ (blue).
  3. Select one of the internal faces.
  4. Click on the ‘Boundary faces’ (pink).
  5. Select the surfaces with openings that lead to the interior.
  6. In case there are cell zones in your model, assign them to Excluded parts. If not, leave it empty.
  7. Hit ‘Apply’ to run the operation.
internal flow volume extraction operation is executed on an electronics box with multiple openings
Figure 3: Creating flow volume for an electronics box using Internal Flow Volume Extraction

If the flow volume operation is successfully performed, you will see the newly created Flow region inside the Scene tree. The default color of the flow region is blue, as in the following picture:

electronics box cad model and internal flow region in simscale cad mode
Figure 4: The internal cavities are filled with the flow region (light blue), and this region is visible under the Scene tree.

Imprint the Geometry

In order to know where the physical contacts between two solids are, we need to perform an imprint. This action basically cuts the interface between two bodies in physical contact into recognizable surfaces. Please refer to our article where a detailed explanation of what an imprint does is well mentioned.

As a result, when we create the CHT simulation, the tool detects the interfaces automatically. If you need to, you can further change the thermal properties of the interfaces.

imprint function in simscale cad mode is necessary for using the model in a cht analysis
Figure 5: To be able to use the CAD model in a CHT analysis, you need to imprint the model.


This is only necessary if you have a CHT simulation (or when you want to see the heat transfer through the walls/solids). If you need to perform an incompressible, compressible, or convective heat transfer analysis, you need to delete the solid parts.

After all the operations are concluded exit CAD mode by clicking on ‘Finish’. This will direct you to the Workbench.

exporting the edited cad model from simscale cad mode to the workbench
Figure 6: Export the CHT-ready CAD model to the Workbench by clicking on the Finish button.

After exporting the edited CAD model to the Workbench, you will see the new model named with “Copy of …” prefix. To clarify, you need to use the new model in the CHT analysis.

automatically detected interfaces in a cht analysis
Figure 7: Interfaces are detected automatically if the Imprint operation is performed. Successful imprint operation is necessary to detect surfaces between parts that are in direct contact.

If the above example caught your interest, quickly jump to the Thermal Management: CHT Analysis of an Electronics Box tutorial where you will learn to visually inspect and manage the temperature distribution inside an electronics box.


If none of the above suggestions solved your problem, then please post the issue on our forum or contact us.

Last updated: May 26th, 2021

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