need help & advise

I can not achieve a uniform homogenous fluidized powder in my fluidized bed; the size of my fluidized bed is 450mmW x 450mmH x 2500mmL; below the porous plate is the air chamber 450mmW x 100mmH x 2500mmL; i am using compressed air with a pressure of 1.5 bar entering at both ends of the air chamber thru 1/2 inch pipe.    please advise how to remedy this problem.

Thank you,

Lydio