Simulating Condensation in Fluent
 

I am simulating condensing, hot, pure steam (air) through a CD nozzle. However, the simulation has been very unstable regardless of the multiphase model I chose. The flow actually becomes supersonic (obviously wrong). I have the following questions if anyone can shed some ideas on:

1. Am using the Mixture model (and tried VOF) with both cavitation (Zwart model) and evaporation-condensation (Lee) mechanisms. Can I use more than 1 mechanism for phase change? If I am just simulating condensation, should I set the evaporation frequency to 0?

2. I assumed the vapourization pressure and saturation temperature in the mass transfer mechanisms the ones that we read of the steam table, i.e. Psat = 101325 Pa at Tsat = 373.15 K?

3. I remember reading something in the literature that Fluent does not model condensation well, one must use an UDF with it. Is it still the case with Fluent 19?

Thanks.