A probabilistic heat transfer model for turbulent fluidized beds

Abstract

A probabilistic heat transfer model was developed that allows for the gradual evolution of bed-to-surface heat transfer coefficients with increasing superficial gas velocity when bubbling and turbulent flow structures co-exist. The model is based on the packet renewal theory and the probability of particle packets for the specific hydrodynamic regime adjacent to the heat transfer surface. Assuming distinctive two-phase flow, dense packets at minimum fluidization voidage and voids almost free of particles, causes the heat transfer coefficients to be underestimated in the turbulent flow regime. By allowing for contributions of structures of intermediate voidage that reflect typical behavior in the turbulent flow regime of fluidization, heat transfer predictions are improved significantly. The resulting model is shown to give good agreement with experimental heat transfer data for fluidized beds of FCC and Alumina particles, changing smoothly from one flow regime to another in columns of different diameters and from the core of the bed to the wall.