TORTUOSITY OF BUBBLE RISE PATH IN A LIQUID-SOLID FLUIDIZED-BED - EFFECT OF PARTICLE-SHAPE

Effects of particle properties on the rise of single bubbles in a liqu id-solid fluidized bed are studied by focusing on the particle-shape e ffect at various bed voidages near incipient fluidization of glass bea ds and sand particles. Experiments, covering the bubble-size range 6-3 7 mm and solids holdups as high as 0.94 times that in tile packed stat e, are conducted in a 2-D column to directly observe the possible rela tionship between the rate and tortuous path of bubble rise. The shape effect, being significant when the close-range (surface-to-surface) in teractions between the particles are predominant, is appreciable for t he relative solids holdups exceeding 0.9. Marked reduction in the bubb le rise velocity is observed as the bubble size is decreased below 8 a nd 12 mm for the spherical glass and irregular sand particles, respect ively, This anomalous reduction stems partly from the tortuousness in the rise path and partly! from thr ''hesitation'' in the net vertical movement. The former, in particular, is quantified ill terms of the to rtuosity of the 2-D rise path. The results support the peculiar trend in the rise velocity observed especially for the sand particles.