| Circulating Fluidized Beds (CFB's) have found increasing use in such applications as fluidized catalytic cracking, coal combustion, and calcination. For the proper design, operation, and control of a circulating fluidized bed, reliable design correlations to predict the heat transfer coefficient are important.;In order to determine accurately the radiative and convective heat transfer in a high temperature two-phase flow heat exchanger, careful considerations were given in design and fabrication of the test facilities. In the experiment, radiative heat flux was directly measured by a radiometer and total heat flux was directly measured by calorimetry. Experimental tests were carried out using two different test particles (FCC and Sand), covering a range of solid particle densities and mean particle size (88-264 ;From the experiments, the three major heat transfer mechanisms (gas convection, particle convection, and radiation) could be quantitatively delineated. In particular, the effect of particle size, temperature, suspension density and gas velocity on particle convective heat transfer coefficients was investigated. Particle convective heat transfer coefficient showed strong dependence on suspension density and particle size. For a given suspension density and particle size, two regions of heat transfer coefficients were observed. Associating this with two flow regimes, a preliminary flow map was obtained to predict the regimes.;From the measured radiative heat flux and temperature difference between suspension and wall, bed suspension emissivities were determined. The experimentally deduced suspension emissivities were found to be in good agreement with emissivities calculated based on independent scattering theory. At the constant suspension density and temperature, smaller particles showed higher emissivity than larger ones. The contribution of radiation to total heat flux was found to range from 40% to 50% at the operating temperature of 450-550... |
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