[aminhgn]

Hello,

I am working on the mass transfer between water and humid air(water vap-air). The mass transfer occurs blow than saturation temperature in falling film parallel flow system which means the temperature of water and air are 25 and 30, respectively; and air and water enters from the top and exit at the bottom. I am using VOF for the multi-phase(air-water) and species model for the humid-air. Firstly, Can I use the default evaporation-condensation model as mass transfer between them? or I have to use UDF to define mass transfer? If, I can use default model, how much are the saturation temp and evap-cond coefficient? If I have to define UDF, should I use mass transfer in multiphase of add UDF as source?

Regards,

Amin

[vinerm]

You don't need UDF for this. You can use Evaporation-Condensation model.

[aminhgn]

Originally Posted by vinerm

You don't need UDF for this. You can use Evaporation-Condensation model.

Thank you for your kindly reply. So evaporation and condensation model is applicable for lower than saturation temperature!? In that case, the coefficients and the saturation temperature are!?
Many thanks in advance,

[vinerm]

Phase change never takes place above or below saturation temperature; then saturation temperature has no significance. However, saturation temperature depends on pressure. So, in an almost dry air, water evaporates at much lower temperature because the partial pressure of vapor in air is much less than saturation pressure corresponding to water temperature.

[lei]

Hi, as vinerm already well said, for a humid air - water system, the saturation pressure need to be modeled as function of the water-vapor partial pressure in gas phase for evaporation-condensation physics.
You could check this article here for an example:
https://udfstore.com/udf-blog/f/udf-...into-humid-air