modeling of two phase flow combustion in fluidized bed with MFIX
 

I want to modeling of two phase flow combustion in fluidized bed with MFIX and have these problems. I will be pleased if anybody can help me.
Did you suppose that the gas was incompressible?
I have problem with sign of void fraction that sometimes it goes less than zero. What’s your opinion to overcome this problem?
What’s your idea for the values of relaxation factors?
Is it possible to modeling this case in steady state condition?