If I understand correctly, you will not get 0 value because of flow in direction paralel to water surface.
I'm not sure if you will get in FlowSimulation movement in relation to humidity.
Perhaps In order to get water vaporation you need to apply some temperature.
Thank you Stefan for your answer.
I think the problem of parallel flow is possible... There is some trick to place the control volume (coincident or not with meshes, etc.) to avoid it?
For temperature, I define initial and limit water and air temperatures. I just not consider things like day/night cycles, etc...
I try to better explain my basic question, because I realized it is not so straightforward...
I have to model the evaporation rate from a water surface (a lake) under several wind conditions, in Cosmofloworks (SW 2008)
I would like to find an evaporation rate under different wind velocities.
I can start with a simplified problem, where the water is static and air and water temperature are constant.
How could I model this system well in SW? Internal or external flow? How to represent the water surface? ...
The first attempt I tried is in my previous post, but I am not sure at all it is the good way!