my problem: 1. how to define a thickness of a solid wall.(the geometry includs only the face of the wall).

2.how to define boundry conditions in both sides of the wall,and mass fractions.

3. where to define diffusion constants for the wall. thank you! hagar

You can't have diffusion through a solid wall. Look in the User's manual for porous jump.

hi evan! thanks for your response. how can i define a wall thickness in fluent? (with no diffusion at all)

You can define a thickness for use in conduction heat transfer in the boundary conditions panel.