haibin wu

Yes, this is a convection problem, not an axial flow problem. I also do not quite understand the setting of the heat transfer boundary conditions for the shell. My current idea is to reduce the problem in the above graph to keep only fluid A, and then set it only for the boundary of fluid A. I don't know that if I only consider the boundary of fluid A, how should I set its boundary conditions? About the surface area and perimeter of fluid a, and the outer perimeter of d, I don't know what this has to do with the thermal boundary setting of wall. Could you tell me about it?thanks