Unfortunately I can’t say exactly what this is for. The heat will come from cylindrical elements on the +z side of the geometry.
I noticed you remeshed with tets, is that better than the hex elements I was using for this application?
Also, what are the options for wall functions and what considerations should I have looking at such a thin channel?
You said that the volume ratio is too high currently, I haven’t calculated y+ yet but I suspect that I won’t be able to use a wall function.