My question was, how to model the resitance as a cylinder with finite thickness, like an actual filter, rather than using surface shell. When I try to that, I get an error that reads : "Material devices (resistance) should have at least two surfaces in contact with fluid."
I know it has more than two surfaces in contact with fluid. So I don't know how to interpret this error.
Understood. It is hard to tell without seeing the exact model. It really should be OK though. I would look at the connections where it meets the walls, are they properly connected or just at an edge? It may also be good to have a solid top to the filter, so it is just a solid cylinder.