Hello,

Here are the answers to your questions.

1. If your gases are likely to be compressible, then you will need to turn on the energy equation.

2. Solver settings depend on the nature of your problem. If you are solving a stiff problem, it might be useful to run a coupled solver. Otherwise, a segregated solver (like SIMPLE or SIMPLEC) might suffice. The primary difference is that the flow equations are solved either in a coupled manner or one after the other. You will find additional details in section **'28.4.3 - Pressure Velocity Coupling'** in the Fluent Theory Guide.

3.For backflow, you can either choose 'Static' or 'Total' pressure from the drop dowm. If you use 'Static', then Fluent will use the specified gauge pressure. If you use 'Total', then Fluent will calculate the dynamic pressure from the velocity in the adjacent cell zone and calculate the pressure based on this and the specified gauge pressure value.

4. The general idea is to pose the problem in such a way that you are sure of the mass fraction of your species in case of backflows. For example, you could have an outlet where only one species is dominant (and the mass fraction of the other species is 0 at this boundary). Please choose your computational domain in such a way that you are able to make that call appropriately.

Since we don't have anymore information about the problem you are attempting to model, I'm not able to answer some of the questions more specifically. I hope this helps.

Thanks.

Best,

Karthik