Boundary Conditions for Bubble Column
 

Dear all,

I am trying to model a Bubble Column. Just to begin with, at the bottom plate in a cylindrical column, I have made some holes to act as sparger holes, and have used it as "velocity inlet" for the gas phase. The rest of the bottom plate has been defined as "outflow", intending to use it as drainout of the water phase. For the top plate, similarly, I have made some holes to act as water inlet, and have used it as "velocity inlet" for the liquid phase. The rest of the top plate has been defined as "outflow", intending to use it as vent for the air. The problem does not converge, and also while checking results at any intermediate iteration, no movement of fluid can even be seen inside the column. Next I tried to use only single phase (air) for both inlets, and then also the problem does not converge. It seems the boundary conditions are not properly defined. Please suggest me a remedy.