Behavior of Bubbles and Heat Transfer Characteristics in a Fine Particle Fluidized Bed Equipped with Immered Vertical Tube Bundles at Lower Gas Velocities

摘要

To establish a rational method for designing a fluidized bed cooler for heat recovery from fine fluidized particles, the bubble characteristics and heat transfer coefficient between a fluidized bed and a heating tube were measured using char particles with a mean size of 70 mum and particle density of 409 kg ·m~(-3) in a fluidized bed equipped with immersed vertical tube bundles. The heat transfer coefficient was also estimated by applying the observed values of the variables of bubble frequency and bubble voidage to an existing packet model. The results show that the presence of vertical couses the lateral distribution of bubbles to level off and that the size of bubbles ranges from 1.0 to 1.4 cm independent of gas velocity, bed elevation and tube pitch. In is also found that the estimated values of heat transfer coefficient agree well with the observed values for relatively small tube pitch, but are systematically smaller than the observed ones for relatively large tube pitch and for a single tube.