# Saturation temperature UDF for evaporation-condensation

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 April 13, 2021, 10:42 Saturation temperature UDF for evaporation-condensation #1 Member   Obi Join Date: Jul 2016 Location: Canada Posts: 45 Rep Power: 10 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?

 June 20, 2021, 10:08 #2 New Member   Stanlee Join Date: Aug 2017 Location: New Zealand Posts: 19 Rep Power: 8 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？

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