Investigation of Hydrodynamics of High-Temperature Fluidized Beds by Pressure Fluctuations

Hydrodynamics of a gas-solid fluidized bed at elevated temperatures was investigated by analyzing pressure fluctuations in time and frequency domains. Sand particles were fluidized with air at various bed temperatures. At a constant gas velocity, the standard deviation, power spectrum density function, and wide-band energy of pressure fluctuations reach a maximum at 300 degrees C. Increasing the temperature to this value causes larger bubble sizes and after the bubbles reach their maximum size, they break into smaller bubbles. The Archimedes number decreases with higher temperature and the type of fluidization becomes closer to that of Geldart A boundary at this maximum temperature. Based on estimation of the drag force acting on the emulsion phase, it was concluded that 300 degrees C was a transition temperature at which the drag force reaches a minimum due to a significant change of interparticle and hydrodynamic forces.