HEAT-TRANSFER FROM VERTICAL SURFACES TO DENSE GAS-FLUIDIZED BEDS

Heat transfer to beds of solids fluidized by gas has been measured from bed walls and from small diameter heated cylinders immersed in the fluidized solid. The experiments have been carried out in beds of 90 mm and 290 mm dia., for different bed depths, for different locations of the heating surface within the bed and at the walls. The size of particles was varied from 100 mum to 1 mm in diameter, in three materials, glass, Diakon, and nickel. Four different distributors were examined. By varying the position of the heating surface at the walls it has been found that there is a significant variation in heat transfer with distance from the distributor. By varying the diameter of the bed it has been found that peak heat transfer coefficients are greater in the smaller diameter bed, but the dependence of heat transfer coefficient upon velocity peaks sharply in the smaller diameter bed with a more gradual change in the larger bed. The experimental measurements have been expressed in the form of a correlation of Nusselt upon Archimedes group, and upon a thermal capacity group. The dependence of Nusselt upon the thermal capacity group is much greater than previously reported.