WALL-TO-BED HEAT-TRANSFER IN GAS SOLID FLUIDIZED-BEDS - PREDICTION OF HEAT-TRANSFER REGIMES

When studying heat transfer between a fluidized bed and immersed surfaces, three modes of heat transfer can occur, viz. conduction (particle convection), gas convection and radiation. A classical definition of the dominant mechanisms is the following: (1) particle convection dominant: d(p) < 600-mu-m; (2) radiation significant: T(b) > 900 K; (3) gas convection significant: d(p) > 600-mu-m. A new definition of the 'heat transfer regimes' is presented in a particle diameter vs. temperature diagram. The discussion on the transition between the various 'regimes' is based upon (i) the Saxena and Ganzha classification scheme combined with Ergun's equation, and (ii) dimensionless numbers related to the ratios between conduction and radiation and between convection and radiation in porous media.