water-air interface is not in dynamic equilibrium
 

Hi experts

I am simulating a falling liquid film evaporation, see the pic.

Laminar, Mixture, Condensation-evaporation Lee model with a UDF defining the saturation temperature (based on the vapour partial pressure) was used. The mass transfer is indeed on the interface, which means my UDF work? It is a steady-state simulation. The settings are shown below. The water vapour- air mixture is incompressible.

I expect the RH will be equal to 100% around the water-air interface, but in fact, the simulation results show that the RH near the interface is far lower than 100%.

Does anyone have any idea about the reason?

Regards
https://forum.ansys.com/uploads/594/GG4DWA7QMBAX.png
https://forum.ansys.com/uploads/756/9EKTU95CDCN3.png