FAILURE BEHAVIOR OF AERATED FINE POWDER BEDS AND THEIR TRANSITION TO FLUIDIZATION

Failure behavior of fine powder beds by upward air flow was investigated experimentally with a two-dimensional column to clarify the mechanism of agglomerate formation in the bed. To analyze the crack formation process the stress distributions in beds of uniform structure were calculated with the finite element method based on an elastic model. In any case the first step of the failure process was crack formation by the pressure gradient due to air throughflow. in the bed. However, the second step depended on bed conditions. In beds of cohesionless powders, the particles around cracks were easily agitated and locally fluidized by the penetrating air. Similar situations were observed in the case of cohesive powders if the bed was loosely packed. In beds of densely packed cohesive powders no agitation-and fluidization were created immediately. Primary cracks were formed at the bed bottom on wall sides. The stress distribution prediction by the finite element analysis with the elastic bed model provided satisfactory implications for the observed crack formation.