Calculating mass flow from a boundary without any velocity
 

Hi there,

I am trying to examine the flow rate of a volatile gas from a surface, simulated here as a boundary condition of pure gas and examining its flow into the domain. However seeing as I am simulating a pool of the gas on the floor and thus the boundary has no velocity, when i try to post Process it using the flowRatePatch function, the cumulative phi turns up as 0, despite the fact that in paraFoam I can see the gas entering the domain.

So my question is, is there another way in which i can measure the flow rate of the gas from the patch into the domain? Any help would be greatly appreciated.