Bed-to-wall heat transfer in a gas-solid fluidized bed with external solids circulation:Modified packet renewal model

摘要

A pilot scale experimental setup was constructed to investigate the effect of hydrodynamics on bed-to-wall heat transfer in a gas-solid fluidized bed with external solids circulation. The bubble size and velocity are increased rapidly with gas velocity at bubbling fluidization. The increased gas velocity promotes the increase in bubble frequency at turbulent fluidization. The external solids circulation can break up bubbles, attributing to the decrease in bubble size and velocity and increase in bubble frequency. The bubble properties are employed to calculate the packet parameters in the packet renewal model. And the packet residence time plays a dominated role in the heat transfer process. The heat transfer bypass occurs due to poor solids radial mixing and external solids circulation. Two correction factors are introduced to modify the Mickley and Fairbanks' model, and the results show that the modified model can predict the heat transfer coefficients successfully.