Density fluctuations in fluidized beds

The effectiveness of fluidized beds is limited by the presence of density fluctuations such as those caused by gas bubbles. The size and frequency of such bubbles were measured in airfluidized beds of glass beads and silica‐alumina catalyst with a gamma‐ray absorption technique used. The results showed that the gas bubbles developed owing to an influx of gas from the continuous dense phase. With increasing elevation in the bed the volumetric rate of bubble flow approached as a limit the total air flow minus the flow through the dense phase corresponding to minimum fluidization. The growth rate of bubble diameter was as much as 0.17 in./in. of elevation. Fluidization was most uniform with the cracking catalyst, for which the apparent density of the dense phase decreased with increasing gas velocity.