Flow rate computation.
 

I would like to compute the integral of the mass or volumetric flow rate across the threshold of a doorway in a 2D model. I don't see any boundary type that would allow a creation of a line across the threshold in a report of mass flow rate, and I don't see a choice for computing either flow rate in the graphics window in results. Am I even going about this computation the right way? Am I missing something simple? I am a new user to Fluent 14.5.7. I used the meshing tools inside Fluent to generate the mesh. -Thanks.