Minimum fluidization voidage in the beds of three kinds of silica is i
nvestigated at elevated temperatures up to 1223 K experimentally and t
heoretically. The bed voidage depends not only upon the operating temp
erature but also upon the humidity of fluidizing gas. Experimental res
ults and theoretical consideration on the change in the bed voidage wi
th temperature and/or humidity demonstrate that this change is caused
by the adhesion force of silica particles originating from the change
in the concentration of siloxane groups on the surface of the particle
s.