Umf is the minimum fluidisation velocity for a bed of particles. An increase in the superficial gas velocity from 2 Umf to 2.5 Umf results in (all velocities are smaller than the entrainment velocity of the particles) no change in the_______________?
(A) Drag on particles
(B) Drag on column walls
(C) Bed height
(D) Bed voidage

