Learning Forum

[Abdullah Hassan]

Hi,

I am having an issue in ANSYS simulation. I am trying to do condensation of water vapor to water liquid but when I initialize the solution, it says latent heat cannot be less than zero. 

I tried to search online & it comes to my knowledge that it is related to enthalpy. 

as enthalpy of liquid is -2.858e+08 and 

enthalpy for vapor is -2.418e+08 at standard temperature. so change in enthalpy is coming negative which means the latent heat is less than zero. 

Can anyone help me, how to resolve this issue or what values I need to choose for enthalpies in this case.

 

NOTE: I already did the simulation for water boiling/evaporation and I didn't face such issue in that particular case. 

[Rob]

If you're using the Evaporation/Condensation model the To and From phase matters. I always have to check the manual, but if you currently have the vapour in the To field switch that to the From field. 

[Abdullah Hassan]

I understand that, what I am trying to do is Condensation of water vapor at 100 C, 

for this case 

From phase should be "from vapor' 

to phase should be like " to liquid".

when I did this, it said latent heat can not be less than zero. 

but when I do the opposite 

from = liquid

to = vapor 

system doesn't shows any warning. Infact it also did the condensation upon putting water vapor at inlet volume fraction as 1. 

 

 

I don't understand that. can you please help

[Rob]

It's because Fluent doesn't know which material is gas and which is liquid. All Fluent does is look at the material data and then add/remove energy based on the formation enthalpy. To get around this, the To and From phase definitions matter: hence my comment about checking.