Learning Forum

[FaizanYounas]

Hello there.

I'm running a phase change simulation in fluent using the LEE model, it's a condensation case. For that, I need to add the source term in the energy equation. I know that I can do this with the DEFINE_SOURCE macro. But, I'm not good with the UDF's right now. I made one but it's not working. I went through the Fluent User Manual and came to know that I can add the source term using the following command:

solve/set/multiphase-numerics/heat-mass-transfer/alternative-energytreatment

I tried and it's working. I can tell from the results that the source term is being added. But, I don't know where to put the latent heat for that energy source. So far I know that the difference between the SSE is taken as the latent heat. First, I'm a bit confused about the units. The unit for SSE (standard state enthalpy) is J/kgmol and for latent heat is J/kg. Secondly, I want to add the latent heat as 329,400 J/kg, in order to add this value as a difference between SSE. Should I subtract the SSE of liquid from vapors or it's the other way around. I went through the user manual again but couldn't understand much about how fluent takes the latent heat.

Please let me know if anyone have an idea about this.

[Rob]

The kgmol is an Americanism for kmol. Don't ask, it made sense in Fluent 2 (or 3) and hasn't been changed. Assuming you're no reacting anything then the latent heat is the difference between the formation enthalpy of the liquid & gas: the absolute values don't matter so set one or other as zero and work from there.

[FaizanYounas]

Thank you very much for the reply. It really solves the problem