Instantaneous local heat transfer and hydrodynamics in a circulating fluidized bed

Local heat transfer mechanisms and hydrodynamics are studied in a 9.3 m tall, 152 mm i.d. transparent cold model circulating fludized bed for 171 mu m Ottawa sand. Instantaneous measurements at the wall are made with platinum-coated heat transfer probes. For some conditions, simultaneous local voidages are determined using a capacitance probe. Results show that the sudden and dramatic peaks in the measured instantaneous heat transfer coefficients are directly caused by the arrival of strands of particles at the heat transfer surface. Analyses of the capacitance probe signals indicate that these strands possess wide distributions of voidages which vary with the local time-averaged area-averaged suspension density.