I am a relative newcomer to CFX 4.4, and I have a couple of (ok, maybe a few) questions concerning some processes I am trying to model.

I am trying to simulate filling a pressure vessel with intermittent venting (meaning that the tank pressure and the mass of fluids in the tank do not remain constant). I keep getting global conservation of mass problems. Is there some way to work around this, perhaps in a user subroutine?

Also, I am trying to model boiling in a tank with an ullage. I need to simulate 1) the stratification/destratification in the tank as boiling commences, 2) the changes in pressure due to the bubbles breaking the liquid surface and becoming part of the ullage, and 3) how the liquid level changes as the fluid boils off.

I haven't been able to find anything that will allow the disperse bubbles to join a continuous gas pocket. Is this possible? Specifically, I would like to model what happens at a "dead leg" of a pipe if a heat leak causes boiling at a closed valve in a line.

I would appreciate any pointers or tips you guys can provide me. Thank you very much.

I have performed smulations in CFX 4.3 on the filling of an evacuated vessel. This was not too difficult as long as the pressure ratio was not below 0.4. (Ratio = pressure inside the vessel/pressure outside the vessel)

Some settings were 'compressible flow' and adaptive time stepping'

When Mach > 1, more settings were required but I can't remember them right now. If you're interested I can look them up for you.

Astrid