Hi everyone. My problem is a bubble columm (water-air). There is an inlet of air in the bottom e i would like that just this air get out in the top. My question is: Who can i put a boudary condition that just the air massflow out and the water not?

Thanks

One way of doing this is, extend the height of the bubble column over the liquid height and patch it with unit vof of air. This will make the water to stay in the system and not go thru the pressure outlet/outflow boundary condition for the outlet. Better free surface conditions such as "Degassing boundary condition" are available in FLUENT as UDF's

And how can i use the UDF? Do you have some example of this kind of boundary condition? Degassing boundary?

I never tried to use the degassing boundary condition UDF by myself, but u can get it from the FLUENT UDF archive examples. The procedure how to use it is explained clearly in the UDF. Goodluck..!

thank you very much!!!!