evaporation from surface with jet impingement

Andrea

Hello, there's something strange.. We are modelling a jet impingement drying (steady state, 2d axisymmetric). We want to simulate the evaporation from the surface impinged (a wall). We activated species transport with 2 species: air and water vapor. We built a UDF to specify mass fraction of water vapor at wall: it calculates the mass fraction corresponding to saturated conditions for water vapor f(T, P). We set 0% mass fraction of H2O at the inlet

Results: INLET mass flow: 1,1374 10e-04 kg/sec

mass fraction of AIR: 99,6 %

mass fraction of H2O: 0.4 % OUTLET mass flow: 1,1374 10e-04 kg/sec (the same)

mass fraction of AIR: 93,7 %

mass fraction of H2O: 6,3 %

It seems that air disappears and water is created. It isn't a physical solution, i think. What we want: water vapor is created and diffuses from surface to the fluid but i don't want to lose air mass.

using a UDF define_source?

P:S: Other settings are: T wall = 320 K, vel inlet = 10m/sec, T inlet =390 K, press outlet = 0 Pa (far from inlet, so without reversed flow). The mesh is fine enough (y+=1)so we used enanched wall treatment with viscous k-epsilon model.