A MODEL FOR HEAT-TRANSFER IN CIRCULATING FLUIDIZED-BEDS

A heat transfer model is proposed for predicting transfer coefficients in circulating fluidizeds beds. Based on observations and on hydrodynamic measurements of the core-annulus flow structure in low- and high-temperature risers, the model assumes that particles in the annulus congregate into strands with different voidages. These strands are assumed to undergo a repeating process of formation, downward movement along the wall, and disintegration. Heat is transferred between the wall and the strands by transient heat conduction with a wall contact resistance. The resulting model gives reasonable agreement with published data for smooth surfaces. It accounts successfully for the effects of heat transfer surface length and particle size. However, it is shown that the effect of the geometry of the heat transfer surface on the flow pattern of particles must be taken into account in future models for membrane or other non-smooth geometrics. © 1990.