Heat transfer characteristics in a pulsated fluidized bed in relation to bubble characteristics

A pulsated fluidized bed is operated with two sequential duration designate d as the on-period with injecting fluidization air, and the off-period with out injecting fluidization air. The heat transfer coefficient between a ver tically immersed heater and bed in a pulsated fluidized bed is measured und er various pulse cycles and fluidized particles. The obtained results are c ompared with those in a normal fluidized bed with continuous fluidization a ir injection. The relation between heat transfer coefficient and bubble cha racteristics, evaluated by using a digital video camera, was investigated. For certain fluidized particles and operated pulse cycles, fluidization of particles and increment of heat transfer coefficient can be obtained under lower mean air velocity based on a pulse cycle duration than minimum fluidi zation air velocity of the normal fluidized bed. Under the pulse cycles whe re a static bed is formed in off -period duration, the improved heat transf er rate in contrast with the normal fluidized bed can be measured. This is because of the large bubbles formation. As the heat transfer in the pulsate d fluidized bed is obstructed with increasing time to keep a static bed due to the excess off-period duration, it is indicated that there is an optimu m off-period duration based on the heat transfer rate.