Reply To: Mass flow outlet boundary condition

[Rob]

I don't follow the bit about Fluent setting liquid even if you have gas. Pictures may help. 

The mass flow outlet was removed for some multiphase several versions back as it wasn't stable. The issue is that if we remove x kg/s and there is a variable amount of a denser phase that the pressure on the boundary becomes unstable. A volume flow boundary (velocity) would be numerically better and potentially physically more sensible as pumps etc suck volume.