2000 Volume 26 Issue 6 Pages 830-836
A pulsated fluidized bed is operated with two sequential duration designated as the on-period with injecting fluidization air, and the off-period without injecting fluidization air. The heat transfer coefficient between a vertically immersed heater and bed in a pulsated fluidized bed is measured under various pulse cycles and fluidized particles. The obtained results are compared with those in a normal fluidized bed with continuous fluidization air injection. The relation between heat transfer coefficient and bubble characteristics, 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 fluidization air velocity of the normal fluidized bed. Under the pulse cycles where a static bed is formed in off -period duration, the improved heat transfer 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 pulsated 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 optimum off-period duration based on the heat transfer rate.