ON OPTIMUM TRANSFER COEFFCIENT AT AN EXCHANGE SURFACE IN A GAS-FLUIDIZED BED

A surface renewal model which uses a generalized gamma distribution to represent the expected residence times of particles is developed to describe heat transfer from a transport surface to a gas fluidized bed of solid particles. The observed maximum heat transfer coefficient value at a particular gas mass velocity is predicted using photographic residence time measurements. The average heat transfer coefficient depends on the expected heat pick up of a single particle entering the effective transfer region and the average flux of particles entering the region. Nusselt numbers calculated from the model equation are generally lower than experimental values. The particle flux depends on the bubble frequency which may be related to bed properties. The model may be used with existing heat transfer data to predict the effect of particle and gas properties on surface to bed coefficients and the optimum value for a bed of known particle properties. © 1969.