A stochastic model for particle convective heat transfer in gas-solid fluidized beds

Abstract

Particle convection is the predominant mode of heat transfer in gas-solid fluidized beds of small particles at temperatures below 650 K and near-ambient pressures. The mechanism of heat transfer is unsteady-state conduction between the heat transfer surface and the hot bed particles which contact it in a recurrent, aperiodic manner. The particle-surface contacting is treated here as a stochastic process with the inter-packet periods being described by a constant-rate Poisson distribution and the contact periods by a negative exponential distribution. These features of the contacting process are incorporated into the packet heat transfer model of Baskakov, and expressions for the heat transfer coefficient and its variance are derived. The contact period distribution data of Ozkaynak and Chen for a bed of 245 μm glass beads at three fluidizing velocities is employed to predict the heat transfer coefficient and its variance at the three velocities. The predicted heat transfer coefficients are found to be in excellent agreement with the measured heat transfer coefficients. However, paucity of simultaneous contact-period distribution and heat transfer data has limited further verification of this model.