[obiscolly50]

I want to write a UDF for calculating the saturation temperature in a multiphase domain for simulating evaporation and condensation. I'm using a mixture model of the simulation. My domain consists of 2 phases:
1) Water vapour and air (modelled as a mixture of species)
2) Water liquid.

For the mass transfer, I believe the saturation temperature is the temperature of vapour condensation or liquid evaporation according to the Lee model. My thought is that to calculate the saturation temperature on a cell by cell basis, there could be 3 instances:
a) A cell only contains water vapour and air: In this case, the partial pressure of water pressure is used to calculate the saturation temperature (temperature of condensation)
b) A cell only contains water liquid: In this case, the pressure of the cell is used to calculate the saturation temperature (temperature of evaporation)
c) A cell contains a mixture of moist air and water liquid, the fraction which can be determined by using the C_VOF() macro.

Can someone tell me if my thought process is right for this problem? The last scenario is where I'm a bit confused. How can I deal with this scenario of 2 different phases occurring inside a cell? My thought is this would lead to a calculation of 2 saturation temperatures and mass transfer is likely to occur between both phases within the cell. This phenomenon is most likely to occur at the interface. If I have two saturation temperatures for both phases, which do I return to the UDF function?

[stanlee8]

I don't understand why you will get two Tsat.
Say you have already determined which cells are at the interfere, using C_VOF, then you can use the mole fraction of water vapour to find out the saturation temperature. Isn't it？