domain selection
 

I have two different phases to deal with, a flow of air in a cylinder over solid particles.....a two domain problem but not a multi-phase one. How can I loop over the cells of a distinct domain among two different existing domains? How can I select one of my domain?
Thanks in advance.

Does anyone know the answer? If yes, I would be appreciate it. Or even if you need more information, let me know.
Thanks alot.