5. Heat and Mass Transfer

Abstract

Publisher Summary Heat transfer in fast fluidized bed (FFB) is of great importance for design and operation. One of the remarkable features of the FFB is its very high heat transfer rate. Because of extensive solids mixing in the FFB, the heat transfer rate between particles is several orders of magnitude higher than that of silver by conductive heat transfer. The heat transfer rate between a wall and a gas flowing through a fluidized bed of granules is at least one order of magnitude higher than that for the same flow conditions in an empty column. But when the gas velocity is increased to reach the fast fluidized regime, the rate of transfer decreases because of decreasing bed density. This chapter discusses heat transfer in fast fluidized beds between suspension and immersed surfaces to demonstrate how heat transfer depends on gas velocity, solids circulation rate, gas/solid properties, and temperature, as well as on the geometry and size of the heat transfer surfaces. Both radial and axial profiles of heat transfer coefficients are presented to reveal the relations between hydrodynamic features and heat transfer behavior. Heat and mass transfer between gas and solids in fast fluidized beds are then discussed. Finally, the chapter states that the key to enhanced heat transfer is the frequent renewal of the cluster layer at the surface by minimizing its continued development.