SimScale CAE Forum

Can not select simulation domain in CHT



I am trying to simulate the heat transfer and distribution of a thin (1µm) heated membrane connected to a bulk material acting as a heat sink in different atmospheres.

Doing a heat transfer simulation works, but the CHT simulation is greyed out when i want to select it. And if I create a CHT simulation I can’t select my geometry.


What could be the cause for that? Do I have to change my model somehow?

Thanky in advance.

Best wishes,


Hi Elmar,

You have to take into account some things:

  • Single solid geometry not supported for CHT

  • STL not supported by analysis type

Does that apply in your case?




Hi Jousef,

thank you for your answer.

The model consists of several solid parts, but it is indeed a STL file.

I have already tried several of the other supported file formats, but the thin membrane (1 µm, in comparison the base area of the model is 1 mm) will, after uploading, consist of only sheet bodies, that can’t be converted back to a solid body. I think 1µm is to thin for either saving or loading properly in that formats. Any help is appreciated.

Here is a comparison of the membrane between a step file (exported from freecad) importet into solidworks and uploaded to simscale:



The problem is clearly visible.

Best regards,


Hi Elmar!

I will forward this to my CAD team, maybe they can comment on that issue!

Thanks for the information!



Hi Elmar,

  1. Regarding your stl model: We do not allow stl-based models in CHT analyses even if they consist of solid parts only. The main reason is that we can not reliably detect the contacts / interfaces between these parts the same way it works for parametric models. It is also quite challenging as often curved parts are not coincident after being triangulated. We also almost never see the use case to be honest. As you have a parametric representation of your model as well, we can work on this one, I guess.

  2. Regarding the sheet body problem with your parametric model. Collapsed solids like we see them as sheet bodies in your model can be caused by modelling tolerance issues or for extremely small entities that we try to simplify during the upload. Meshing those would be usually a big pain though. Is it possible in your use case to model the membrane as thin layer resistance?

Best regards



Hi Alex,

thank you for your answer.

  1. I can export or save my model to several different file formats, that is no problem. STL was just one I had already heard of and it had already worked for a heat transfer simulation :).

  2. I am not exactly sure what I have to do to use a thin layer resistance model for the membrane. Or how to model it in my CAD programm. I am quite new in both, simulation and modelling. The membrane then would be a layer without actual thickness? As long as it is still possible to simulate heating on a part of the membrane, heat transfer and distribution of the temperature with the surrounding atmosphere and material connections it should be ok.

And maybe I can change my model, replace the bulk material with a constant temperature boundary condition and scale it up a bit. I have to think about that and try it.

Best regards,