Gas-to-particle and particle-to-particle heat transfer in fluidized beds of large particles

Abstract

Gas-to-particle and interparticle transfer rates were measured, at room temperature, for three different materials, in the range 1 ≤ U/ U mf ≤ 3.5 and 0.900 ≤ d p ≤ 2.250 mm by means of batch runs in which wet capillary-porous particles were dried in fluidized beds of similar dry ones. It was observed that gas-to-particle convective transfer coefficients vary only slightly with the air velocity. A “slow-bubble model” convenient for large particle fluidization, was developed to explain this finding and provided interesting data concerning the gas flow distribution in beds of large particles. The particle-to-particle heat transfer coefficients, nearly independent on the particle thermal properties, were correlated by the following equation: h pp = 206 d p −1.22 ( U/ U mf ) −0.56. A theoretical analysis of the interparticle heat transfer confirmed the observed trends and its application to our results allowed to estimate the dense phase expansion.