mass flow inlet condition is not properly specified in circulating fluidized bed
 

Hello
I am working on a circulating fluidized bed
i have done the 2d geometry with velocity inlet, mass flow inlet and pressure outlet as boundary conditions
it is the case of two phase flow(sand and air) initially i patched the solid volume fraction at a certain height for giving the boundary condition for sand.

when i am simulating with transient condition after some time step the problem conversed well

But my problem is after more time step the bed is full of air only there is no sand particle in the bed i thing the mass flow inlet where i gave the mass flux(for sand ) is not properly working
another problem while the sand particle flows from bottom to top it is not scratched and it flows continuously and when it reaches at the top part of the riser then the bed is full of air only