Reply To: Fluctuations and overshoots in the flow rate of ethanol at the outlet.

[Rob]

Sounds right. Buoyancy forces will alter the flow field and if you don't get the boundary pressure right it'll do strange things. 

Back flow conditions are set in the pressure outlet panel and define what comes into the domain when backflow occurs. In your case you'll be setting direction (from neighbouring cell is a good choice), temperature and species volume fraction.