# defining mixture of gases in a domain

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 May 31, 2018, 10:35 defining mixture of gases in a domain #1 Member   Muhammad Ali Uzair Join Date: Sep 2017 Posts: 44 Rep Power: 7 Dear all, i am simulating a species transport problem. For that, I have to define mixture of gases by volume percentage (CO2+H2O+O2+N2=100%) in a rectangular domain. How can I do that? Thanks

 May 31, 2018, 11:08 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,246 Rep Power: 63 Do you have a species transport problem or do you simply want to model it as a mixture of gases? It doesn't mean the same thing. Specifying the gas mixture in the domain is done in cell zone conditions. In a species transport problem, you don't know the composition beforehand, you have to solve for it with the calculate button. Here you only give an initial guess.

May 31, 2018, 11:17
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Quote:
 Originally Posted by LuckyTran Do you have a species transport problem or do you simply want to model it as a mixture of gases? It doesn't mean the same thing. Specifying the gas mixture in the domain is done in cell zone conditions. In a species transport problem, you don't know the composition beforehand, you have to solve for it with the calculate button. Here you only give an initial guess.
Thanks dear,

how can I do it in cell zone conditions, i.e. defining mixture by volume percentage?

tbh my problem is like this; there is an inlet of air, and then there is a mixture of gases with known percentages of volume inside the domain. and I have to do the species transport.
and I cannot use the species transport, then what is the way to to that?

 June 1, 2018, 20:11 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,246 Rep Power: 63 Ok so you need to use the species transport model. Specify the composition of air at the inlet as a boundary condition. For the interior with a predefined mixture, you would specify the mass fractions as the initial condition in the initialization. Normally you would specify mass fractions because that's the primitive variable in the species transport, but sometimes you are allowed to specify mole fractions. m.uzair likes this.

 Tags domain, fluent, mixture, species transport model, volume fraction