I´m trying to solve a very simple problem in Fluent where I have a model with a couple of different materials and wants to calculate the temperature distribution. When reading the case into Fluent the program automatically turnes some of the boundaries between the different materials into walls. The rest of the boudaries are still referred to as interior. When calculating the temperature distribution these walls seems to be completely isolated and no energy is transfered over the walls. I want to change the boundary type into something else, but there seems to be no good alternative. Is there any other way of getting around this problem?

I have solved this kind of heat transfer problem many times but this obstacle have never occured earlier, is it a problem that has its origin in Gambit where I generated the grid?

Change the boundary type from wall to interior for these odd BCs. If for some reason the code wont let you do that the meshes may need to be fused first: Geometry > Fuse. If neither of these two approaches work the meshes on either side of the wall are probably non-conformal.