Particles are unlocked and the bed expands from an height of
Bed continues to expand
(for liquid only) till there is a carry-over of solid particles
For gas–solid system, bubbly or segregated fluidization is observed, with large-size bubbles–formation .A qualitative graph showing the variation of packed–bed height and pressur–drop with the superficial velocity of the liquid is produced below:
(Fig. 32b)
Fixed bed of height and porosity
The bed expands at (minimum fluidization velocity) from
The bed continues to expand with increase in the bed porosity from to higher porosity
and porosity 
(minimum fluidization velocity) from 
to higher porosity 
