Hello Everyone. In my simulation I mix two gases. Initially in the half part of the chamber are air (volume fraction of the air is 1) and the in the another half part are neon (volume fraction of the neon is 1). The problem is when I check the volume fraction of the air anywhere in the chamber (in case of steady state simulation) is not 0.5. In this case the mixture are in a state of equilibrium. And the volume fraction of air or neon must be 0.5. Thanks for the answer.