Recently I ran into some problems.

I simulates a count-flow with two phase, ie: some kind gas flow from bottom to top, some kind solid flow from top to bottom. Therefore, there is a problem, how to define the boundary condition in Fluent, you know, the same line or surface, which considered as inlet for one phase, is however considered as outlet for the other phase.

How to slove the problem? Would you please give me some suggestions?

pressure inlet and pressure outlet boundaries do not prescibe that the fluid will enter or leave the domain. Using the backflow parameters for inlet conditions at the pressure outlet should work.

Many thanks for your suggestion. I will try what you told me.