Reply To: Which solution method (scheme) should I select for multiphase flow (pumping gas to blow water out)?

[Rob]

36 hours isn't too bad, other than more parallel & faster cpu there's not much you can do. Using a coarser mesh will speed things up, but you'll just produce rubbish faster. Some models run in a few 10's of minutes, others can take several weeks or even months: CFD isn't always a quick process.
Re the balance, you need to look at the mass fluxes and volume integral: what goes in must come out or add to the volume mass.