In the Conjugate Heat Transfer (CHT) simulations, the interfaces are required for the heat transfer between two regions. These interfaces are generally created automatically during the meshing process. To enable the mesher to create the interfaces automatically, CAD should have the face cutouts at the mating surfaces.
This is the sample CAD for the CHT application, containing three regions, one fluid region and two solid regions.
In the following image, there are no face cutouts at the regions where this surface is touching the other parts. The entire surface is continuous so, no interfaces will be created during the meshing, and there will be no heat transfer between these regions.
Here, the surface regions, which are in contact with other parts, are precisely cut into separate surfaces. So the interfaces will be created in this case.
Once meshing finishes, the list of interfaces can be seen in the mesh log. In case the faces are not split at the mating surfaces, the interfaces at these surfaces will not be created and will not be listed in the log.
Some CAD softwares delete the face cutouts while exporting. Make sure the CAD is exported preserving these separate faces, and inspect it after uploading it to the SimScale platform.