Hi! I am working on Modeling Species Transport and Gas Combestion with this reaction: (co2 + h2s) + 1.5 (o2+ 3.76n2) = so2 + h2o + co2 + (1.5*3.76)n2 the problem is with the pressure outlet boudary condition. I can't figure out what shall I input as mass fractions there. i think they are supposed to be calculated by Fluent. arn't they? Why can I not change the boundary type to Neuman one? actually, i can only input mass fractions as constants thanks a lot

Just leave them as zero. Fluent does calculate them for you.

Thank you very much John!

These values are the source terms to be introduced in the event of reverse flow (though it doesnt explicitly say so). If no back flow occurs across the zone then you can leave these values but if there is some and they are zero, the medium will be artificially diluted at the exit. In this event, change them to a more realistic value if backflow is physical otherwise extend domain to capture recirculation and prevent backflow, possibly with zero shear walls on this extending section to negate wall shear pressured drop effects.

If you use an outflow it extrapolates the values from the flow domain in the case of backflow but these aren't as stable as pressure boundaries so red lemon's may be a better option.

Phil

i really appreciate! you are very kind thank you for helping me

note that the value is a mass fraction and not a mole fraction