hi,I have met a question in my work.I am simulating the diffusion of fume which is from the chimney to the big space of atmosphere.In the gambit,I make a model of finite size.But I don't know which boundary I should set for the outlet,pressure outlet or outflow?In fact,if I set outflow,the iteration in fluent is converged,but the solution is worse than that of pressure outlet which can not reach converge. Moreover,if I set pressure outlet,there is another question:how to set mass fraction of species in this boundary without knowing the actual data. thank you for any suggestion.

Are you modeling the fume source from within the building the chimney is attached to? Do you know the flow rate through the chimney? Are you instrested in the heat transfer, which will impact buoyancy of the fume?

I'm modeling the fume source withine the big space where there's nothing except a chinmey.I know the rate of the outlet boundary and I am very intresting in heat transfer.Do all these are considered in the setting of boundary condition? expecting for your help.thank you.