Mass flow rate
 

Hi,

I'm running simulation in CFX-Eulerian-Eulerian approach in a rectangular,vertical box with a slot at the top for curtaining particles.I want to achieve mass flow rate at each height by putting plane (horizontal plane).At discharge point the mass flow rate is fine when i extract my data based on X,Y,Z and massflow and sum all mass flows within the plane it gives me the exact amount of mass flow I put in setup for solid inlet boundary condition but gradually by coming down to the base of the box it gives me some negative mass flow rates and at the base plane all of my mass flow rate are negative.I don't know what is the reason.

Cheers,
Sepideh