Learning Forum

[Amir]

Hello,

I am trying to simulate water-vapor condensation, using VOF model. When adding materials from Fluent database, I manually add the values of Latent Heat:

Zero for water-liquid and for Air, and 43987714 j/Kgmol for water-vapor.

When starting the calculation, it gives "Latent Heat can not be less than zero" error.

I tried running the same geometry as an Evaporation simulation (reversed BC and starting with water-liquid at inlet, instead of vapor), it did not give the Latent Heat related error and based on attached contour, seems that Evaporation is actually happening and there is water-vapor in the domain.

I would appreciate any comment on this.

Thanks

[Amine Ben Hadj Ali]

Verify if you are defining the phase change as from "liquid" to "gasesous" phase

[Amir]

 

Thank you DrAmine, I was defining it as “liquid” to “vapor” for Evaporation and as “vapor” to “liquid” for Condensation, the later seemed not to be correct. Changed it as you mentioned and the error did not show up.

[manuel.pacherres]

Hi Emir I just read the problem you had, I just wanted to ask:
 The air that you are considering, will be the cooling fluid ? or is that necessarily to perform the condensation process in Fluent you need to enter air ?

[Amir]

Hi Manuel, in this simulation Air was not playing any role. It was the condensaion of just "water vapor" into water liquid and Air was not needed.

[manuel.pacherres]

I understand Emir, thank you very much for your answer 
If I were to work with concentric tubes where cold water at 22.5°C at atmospheric pressure passes through the middle tube, and water vapor at 105°C at its saturation pressure which is 122300 Pa passes through the outer tube; do you know if I would have to change the properties for both water and vapor according to the inlet temperatures (i.e. 22.5°C and 105°C)?  And at those temperatures, can I also put "0" for the SSE of water in liquid state and 43987714 j/Kgmol for water in vapor state ?

[Amir]

You add the "latent heat" when defining (importing) your material (0 for water liquid and 43987714 j/Kgmol for water vapor) and it does not depend on your boundary conditions (inlet or outlet temperatures). Water in liquid state has latent heat value of zero and in vapor state it is 43987714 j/Kgmol.

I am not sure what you meant by "SSE of water", but yes as I mentioned latent heat should be 0 for liquid and 43987714 j/Kgmol for vapor state.

Hope it helps.