The measurement of instantaneous local heat transfer coefficients in a circulating fluidized bed

Abstract

Abstract Instantaneous and time‐averaged local bed‐to‐wall heat transfer coefficients were measured in a 9.3 m tall, 152 mm ID cold model circulating fluidized bed riser at three different heights for 171 μm Ottawa sand at a superficial gas velocity of 7 m/s, and for solids circulation fluxes up to about 70 kg/m 2 .s. All data were obtained with an instantaneous heat transfer probe consisting of a thin platinum film deposited on a 1 cm 2 piece of glass protected by a thin plastic film. Instantaneous heat transfer coefficients in the riser showed sudden and dramatic peaks caused by strands or sheets of particles sweeping past the probe. Consistent with previous work, time‐averaged coefficients varied nearly linearly with suspension density. The heat transfer coefficient decreased from the bottom to the middle of the column, and then increased near the top due to an increase in suspension density for the exit geometry employed.