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

Heat transfer to beds of solids fluidized by gas has been measured fro m bed walls and from small diameter heated cylinders immersed in the f luidized 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 part icles 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 be en found that there is a significant variation in heat transfer with d istance from the distributor. By varying the diameter of the bed it ha s been found that peak heat transfer coefficients are greater in the s maller diameter bed, but the dependence of heat transfer coefficient u pon velocity peaks sharply in the smaller diameter bed with a more gra dual change in the larger bed. The experimental measurements have been expressed in the form of a correlation of Nusselt upon Archimedes gro up, and upon a thermal capacity group. The dependence of Nusselt upon the thermal capacity group is much greater than previously reported.