VOF - Eliminating shear on the surface of a thin liquid film
 

I'm trying to simulate film evaporation and film condensation by using the VOF method. So there is a liquid film on the wall of a rectangular duct and a mixture of air and water vapor flows adjacent to the film. Based on the relative humidity either evaporation or condensation occure over the film surface.

I have already done this simulation with the Eulerian Wall Film (EWF) model and in the EWF model it is possible to switch off the surface shear at the film surface.

I had to switch this off to make the result i.e.., the rate of mass transfer comparable to some theoretical solutions. So it is like there should be a flow of moist air (air + water vapor) over the film surface but the film velocity has to be zero so that the mass transfer over the film surface is only by evaporation or condensation.

Now by the VOF method i simply patch the cells adjacent to the wall with liquid (water) volume fraction to get the desired film thickness.

Could someone please tell me if it is possible to eliminate surface shear in this case on the liquid (film) surface.

Please let me know if at least a UDF could help in this case.