A STUDY OF THE PARTICLE CONVECTION CONTRIBUTION TO HEAT-TRANSFER IN GAS-FLUIDIZED BEDS

A model for the particle convection heat transfer component of the overall heat transfer between a submerged surface and a bubbling fluidized bed is presented. A convective boundary condition combined with surface coverage concepts are introduced to describe the instantaneous wall-to-bed heat transfer. Both thermally lumped and distributed formulations with constant and variable properties for the model are presented and studied. As formulated, the model is not restricted to uniform bed particle size distributions. Experimental measurements obtained from instantaneous local heat flux probes are compared to the model predictions. The thermally distributed, variable property model formulation provides very good agreement with the experimental data over a wide range of particle sizes and fluidization velocities. For particle size beds ranging from 256 to 4000 mum, the model displayed a very accurate trend prediction relative to available data, with magnitude predictions of 2-28% error, depending upon particle size over a wide range of fluidization velocity.