EXPERIMENTAL-OBSERVATIONS OF VOIDAGE DISTRIBUTION AROUND BUBBLES IN AFLUIDIZED-BED

Air-fluidized beds of two types of powder (groups A and B of the Gelda rt classification) have been examined using X-rays and the voidage dis tributions around individual gas bubbles have been determined. The res ults show that the rising bubbles are surrounded by an expanded ''shel l'' of particles in which the void fraction is considerably in excess of that of the emulsion phase remote from the bubbles. The extent of t he shell is shown to be greater than predicted by current theories rel ating to the steady motion of bubbles in fluidized beds. A simple mode l of bubble coalescence shows that the increase in size of the ''visib le'' bubble volume is caused by inflow of gas from the shell region du ring the process.