Applying equal inlet and outlet particle flowrate in Rocky

[f.jalilijamshidian]

Hello. As you see in the image, I have a reactor filled with particles, lets say 200 g, on the bottom. The is an outlet pipe on the bottom left side. I want to put an inlet particle surface on the top with the mass flow rate of 10 g/s. Meanwhile, I want to have an outlet mass flow rate from the pipe equal to the inlet (10 g/s) so that the inventory mass does not change. My issue is that I do not know how to implement a condition to have the same output flowrate as the inlet for different values (scenarios).

I would be very happy if I heard from your nice ideas.

Thank you so much.