Heat Transport Mechanism around Tubes Immersed in Floating Particles

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Intensive studies designed to realized to fluidized bed heat exchanger with excellent heat characteristics have been cconducted in recent years. While several theories for the heat transfer process have been proposed, actual design currently still depends on empirical correlation.The mechanism of heat transport from a single row horizontal tubes submerged in a floating fluidized bed, of which the static bed height was very shallow, was investigated experimentally. In this paper, in order to improve the performance of a heat exchanger on fluidized, low density particles (polystyrene hollow sphere) were employed.Aiming at phenomenological understanding of the heat transport mechanism, the fast response capacitance sensor mounted flush within the tube was developed to investigate the movement of particles near the surface of tubes. Local instantaneous heat transfer coefficient was also measured using a miniature heat flow sensor for the same conditions.A new model of heat transport mechanism was suggested from the data of capacitance sensor and heat flow sensor. Comparison of this model with many of the other models, in particular the packed renewal model originally developed by Mickley and Fairbanks, was tried.The results obtained were; (1) The capacitance trace versus time can be directly related to the variations in local solids density near the tube surface. (2) Capacitance signals can be divided into three major types as follows; the dense emulsion phase, the lean emulsion phase and the gaseous medium with some entrained particles. (3) Signals of heat flow sensor correspond to those of the capacitance sensor. (4) Heat transfer coefficient rises extremely by the effect of the dense emulsion. (5) Heat transport mechanism can be explained by a renewal model of results were accord with experimental results.