Heat dispersion within organized fluidized system heated in a cylindrical apparatus

Experimental investigation was performed on heat dispersion in the system c omposed of bed of porcelaine spheres between which sands were fluidized by an air stream. The system was heated by the wall of a tubular apparatus. Th e diameters of the spheres and the sand fractions as well as the air flow r ates were varied in individual experiments. It has been found that the generation of the fluidized phase within the voi ds of the bed promotes the longitudinal uniformity of the local heat fluxes transferred from the hot apparatus wall into the system, as well as the ra dial uniformity of the temperature over the system cross-section. The flat radial temperature profiles within the bed with the fluidized phase manifes t high effective thermal conductivity (practically indeterminable) which is responsible for very fast heat dispersion within the system. This is in co ntrast with the bed alone in which the well-marked radial temperature gradi ents manifest rather low effective thermal conductivity. The experiments re vealed that the heat transfer rate from the hot apparatus wall into the org anized fluidized system, like into the bed alone, is determined by the ther mal resistance within the near-wall region of the systems. The Nusselt numb ers expressing the heat transfer rates in both systems can be correlated wi th the Reynolds numbers by the same formula, independently of the sizes of the spheres and of the sands as well as of the fluidized phase density, in the range of gas flow rates applied in the experiments.