Select volume

A cell zone has been defined with assignments of faces. This is not supported. Please create a closed solid region that exactly represents your cell zone in your CAD tool. How do i solve this error??
I use stl format cad , when i upload it ,it creates solid_0 and my radiator comes under this and because of this it gets selected as a face and not as a volume

Hi @markII!

If you want to use MRF zones you have to make sure not to have a face but a volume. Faces are not allowed for a MRF zone which I assume you want to use?