Particle convective heat transfer coefficient, axial

Derive the axial profile of the particle convective heat transfer coefficient in a circulating fluidized bed of fine particles using the information given in 10.4.1. It can be assumed in the derivation that particles in the bed are all in a cluster form. 

Kang, Fan and Kim(96) measured coefficients for heat transfer from a cone-shaped heater to beds of glass particles fluidised by water. They also found that the heat transfer coefficient passed through a maximum as the liquid velocity was increased. The heat transfer rate was strongly influenced by the axial dispersion coefficient for the particles, indicating the importance of convective heat transfer by the particles. The region adjacent to the surface of the heater was found to contribute the greater part of the resistance to heat transfer. 

In Chapter 5, Z. Yu and Y. Jin of THU describe experimental studies of heat transfer between particle suspensions and immersed surfaces, enumerating the effects of variables and of the radial and axial distribution of the heat transfer coefficient. They then present an analysis of the mechanism of heat transfer, particularly in terms of particle convection. 

Beat Transfer, Fluid-bed reactors are characterized by high heat-transfer coefficients on the side walls and on internal heat-transfer devices such as coils or axial bayonet-type tubes, with heat-transfer coefficients ranging from 50 to 125 Btu/(hr)(ft )( F). Coefficients betw een the gas and solid particles of high surface area are somewhat higher than attained under natural convection conditions. For example, a natural convection coefficient for 50-n particles in air is around 200 and, in a fluidized system, this value would be even higher. 

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