Cluster size distribution in the freeboard of a gas–solid fluidized bed

Size distribution of clusters was determined in the freeboard of a 0.05 m diameter fluidized bed using a fiber optic probe at various axial and radial positions and different superficial velocities. The experimental results showed that the cluster size distribution is wider at lower axial positions due to the existence of larger clusters. Size of clusters decreases in the vicinity of the wall owing to wall effects and high rate of contacts between ascending and descending clusters. Studying the cluster size distribution at three superficial gas velocities showed that the size of clusters increases and their distribution becomes wider by increasing the superficial gas velocity. Effect of particle size on the cluster size distribution was examined which indicated that larger clusters are formed in a bed of larger particles.