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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.

    Approach

    Import the following geometries into your Workbench by clicking the button:

    Clicking the link leads to the following Workbench view:

    Electronic_Box_Tutorial_CAD_Edit_1
    Figure 1: SimScale Workbench view

    The project contains two geometries. The first one, named Electronics Box Missing Flow Region, still needs a final CAD preparation step before it can be used in a simulation.

    The second geometry, Electronics Box Flow Region Prepared, is the final complete geometry that we aim for with this approach.

    CHT simulation involves heat transfer through both solids and fluids. 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 solid parts, as you can see in the first geometry:

    an electronics box that will be used in a cht analysis
    Figure 2: The original CAD model of the electronics box, which will be used in a CHT analysis

    To begin creating a fluid flow volume select the geometry ‘Electronics Box Missing Flow Region’ and click ‘Edit a copy’:

    entering cad mode electronics box cooling
    Figure 3: Click the ‘Edit a copy’ button. This will allow you to create a draft of the chosen model, and you’ll be able to perform several CAD operations within the same user interface.

    After selecting the first geometry and clicking on ‘Edit a copy’, a draft of the CAD model will be created for editing. The interface looks as follows:

    entering cad mode electronics box cooling
    Figure 4: The CAD editing tool supports a series of CAD operations that allow, amongst others, CAD clean-up and flow volume extraction

    Next, create an internal flow volume operation by hovering over the Flow Volume icon and selecting ‘Internal’.

    internal flow volume operation in cad mode
    Figure 5: An Internal volume operation will create a fluid domain within a closed CAD body

    To create the internal fluid volume, select a face of the housing that will be adjacent to the boundary face. This will define a starting point (source) for the internal fluid volume creation and is referred to as a seed face.

    Since the housing of the electronic box has two open faces, we have to define two boundaries, which will limit the creation of the internal fluid volume. For the electronic box, select the front and the back of the housing as the boundaries.

    Thermal Management Electronic Box Internal fluid Volume settings
    Figure 6: Setting for the Internal Volume operation. The boundary faces provide limits for the internal fluid volume.

    Once the settings panel looks as above, hit ‘Apply’.

    If the flow volume operation is successfully performed, you will see a newly created solid body 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 7: The internal cavities are filled with the flow region (light blue), and this region is visible under the Scene tree.

    To observe just the flow volume created, hide all the other parts. This can be done by hiding the whole CAD first and then showing only the Flow region.

    flow region show
    Figure 8: Hide the main CAD Electronic Box Missing Flow Region and then show only Flow region.

    Now you can exit CAD editing tool by clicking on the ‘Save’ button (top right, see Figure 7). This will save the latest version of your draft as a new model under the Geometries list named with “Copy of …” prefix. The name can be edited as preferred.

    Interface Detection

    When we create the CHT simulation, the tool detects the interfaces between the solid and fluid regions automatically and hence, no further CAD operation is necessary.

    automated interface detection simscale
    Figure 9: Interfaces are detected automatically and are allotted an interface type by default.

    Note

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

    Last updated: May 16th, 2025

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