Determination of particle and gas convective heat transfer components in a circulating fluidized bed

Low temperature (below 600 K) heat transfer between the wall and two-phase gas and solid flow in fluidized beds has been widely recognized to consist of two components. Particle convection, which is due to the convective exchange of particles of a high heat capacity at the surface and gas convection which is due to the motion and heat capacity of the gas in contact with the surface.; Simultaneous heat and mass transfer experiments were conducted to determine the particle and gas convective components in a cold flow circulating fluidized bed. Heat and mass transfer at the wall was measured for silica sand of 0.150 and 0.400 mm mean particle diameters, FCC of 0.069 mm diameter and steel shots of 0.253 mm diameter.; The Colburn heat and mass transfer analogy was employed using a naphthalene mass transfer probe. Overall heat transfer, i.e., the combined particle and gas convective components, was measured using a heat transfer probe. The particles are immune to mass transfer, thus the mass transfer data is indicative of the gas convective component. The particle convective component was quantified by the difference between the measured overall heat transfer and gas convection as measured by mass transfer.; Wall to bed heat transfer in the fast bed was found to be a function mainly of suspension density. The overall heat transfer coefficient was found to be roughly proportional to the square root of the local suspension density as measured using the pressure drop method. The heat transfer coefficient was found to increase with decreases in particle size at similar suspension densities.; Gas convection measured using the naphthalene sublimation technique was found to account for from approximately 15% up to roughly 95% of the overall heat transfer coefficient. The gas convective component was found to be only a weak function of suspension density.; An empirical model resulting from a modification of the model presented by Wirth (1994) is presented for overall heat transfer predictions. Heat transfer at the wall of a circulating fluidized bed is simplified to be a function principally of the cross-sectional suspension density and particle Archimedes number.