Gas mixture thermo properties
 

Hello,

I have a gas nozzle with a backing pressure of ~1 atmosphere going into a chamber of low pressure. I can solve this for using a gas of only 1 type (oxygen, nitrogen etc) but when I try to use it for a gas of different types, I don't seem to get the answer I expect.

For example, in the Ladenburgjet case, the thermophysicalProperies file is
mixture air 1 28.96 1004.5 0 1.458e-06 110.4;
but if I try and use something like
mixture n2 0.8 28.01 1040 0 1.407e-6 103.5;
mixture o2 0.2 32.00 918.0 0 1.764e-6 139.9;
I don't get the same answer. Is there something else I need to be doing to define the mixture of the gas? I feel like it should be an simple solution. I'm using rhoCentralFoam to solve.

EDIT:
Changing the gases with a much more obvious mass difference still gives me an answer that i'm not expecting. I am using helium and O2, which has a substantial mass and maximum velocity difference. However, I'm still getting an answer that depends only on the O2 and not on the He at all. Even at ratios of 99.9% He and 0.1% O2, I get that the maximum velocity is only dependent on the O2. Once the O2 goes to zero, then I get a maximum velocity of helium.

Cheers.