[flow-mo-mcfadden]

I'm trying to build a Fluent case to study the system shown in the figure but I can't figure out how to establish a boundary condition that represents the positive displacement pump. To be clear my model includes a pressurized steam inlet and a pressurized air flow inlet. I know the outlet diameter so it was suggested that I use a velocity inlet BC at the outlet and reverse the flow direction. I tried this without success (Fluent divergence).

In theory, a 100% efficient positive displacement pump in this application will evacuate the mixing chamber at a fixed volumetric rate. While the volumetric flow rate is fixed the mass-flow adjusts based upon the density of the fluid in the mixing chamber.

This seems like it would be trivial to solve. Any tips on an outlet boundary condition? I would really like to figure out how to get this to work.