Hi Rob, thank you for your reply. From what I remember about this simulation, the air within the domain had a specified air/H2O mixture and the air entering through the inlet also had a specified air/H2O mixture. I have found how to modify the inlet air/H2O mixture (in inlet boundary conditions), but how would I modify the air/H2O mixture of the domain. Is it by going into the internal boundary condition? I could not find anything. Any assistance on this is greatly appreciated. Thanks.