Hello,

When I'm doing a species transport modelling without any chemical reactions involved, eg spread of ammonia gas in a room, thus the mixture is air and ammonia gas.

Is it better to "break up" air into its main constituents eg N2,O2,CO2,vapour or do is it better to "lump" its constituent into a single species material as "air"?

Julie,

It depends what you want to do. If the O2 (or other components) will not be modeled as reacting, then including them as separate components will just take extra computing time.

One thing with CFD modeling, it is pretty easy to try different alternatives. If it works out, great; if it doesn't, sometimes you learn from that as well.

Ok thanks!