Diffusion from fluid region into porous tissue.
 

Can any one help me please?

Im modelling oxygen diffusion from fluid into porous tissue. I want the fluid flow stationary and want to see the effects of the oxygen diffusing into the tissue until equilibrium is reached. When i use the exact boundary conditions needed and include an inlet velocity i get what i would expect for the flow field; so the porosity definitions should be correct. However, when i try to model the species transfer, the concentration of oxygen is the same within the tissue as outside the tissue to start with. Is there a way of specifying a lower concentration of oxygen for the tissue as it wouldn't let me modify oxygen content in the materials panel.

Also, for the diffusion into the tissue, would i need to write a UDF for the source term within the tissue as im new to all this stuff.

Many thanks Lindz