Calculating material concentration profile

Sungyeol

I try to calculating material concentration profile from wall using transport calculation options in multi-component problems. I specially interest micro meter scale profile near wall in large reacting vessel geometry. However, I cannot give a boundary condition in the wall, assuming almost zero concentration in the wall.

Or should I give a source boundary condition in the wall? (In the wall, there are chemical reactions but I just want to model this using source for steady state.)