Effects of solid particle properties on heat transfer between high-temperature gas fluidized bed and immersed surface

Abstract

The effects of particle size, packed density, thermal conductivity and specific heat capacity on heat transfer between a high-temperature gas fluidized bed and an immersed surface are investigated. Hollow-corundum-sphere, corundum, magnesite and quartz sand particles with different diameters within the range of 0.35–1.21 mm are used. A liquefied petroleum gas fluidized bed furnace with 0.3 m × 0.3 m cross-section at hearth bottom and 0.8 m in height is used. The furnace temperature varies in the range of 990–1010 °C, the immersed object is a silver sphere of 20 mm in diameter and the fluidizing velocity is changed from about 1.0 U mf (the minimum fluidizing velocity) to about 3.0 U mf. The experimental results show that, for small particles, d p<0.8 mm, the effects of thermophysical properties of particles on heat transfer coefficient become important with particle diameter decreasing; for large particles, d p⩾0.8 mm, the effects of the properties on heat transfer are limited; and for all particles with diameters in the range of 0.35–1.21 mm, the heat transfer coefficient between the fluidized bed and the immersed surface is insensitive to particle thermal conductivity.