dense particle in air simulation
 

i was using MPPIC foam for particle in air, i was getting good convergence too till suddenly, it shot up, (mean= 0.05, max = 10 , courant number),
i was simulating swirl tubes and particle seperation of sand,
i got 1 failed mesh check (unused points are there)
inlet velocity = 20m/s
outlet pressure = 1 bar
no of particles is 18g sand for 1m3 of air
any idea on how to go about it