Heat transfer and bubble properties in three-phase circulating fluidized beds

Abstract

The heat transfer and temperature difference fluctuations (Δ T) between the immersed heater and the bed proper have been investigated in the riser of a three-phase circulating fluidized bed (0.102 m ID ×3.5 m in height). Bubble properties such as rising velocity, chord length and frequency have also been measured, to analyze the effects of bubble properties on the heat transfer coefficient in the riser. The resultant time series of Δ T-fluctuations have been measured and analyzed by adopting the concepts of mutual information function, phase space portraits and Shannon entropy. The effects of gas and liquid velocities and solid circulation rate on the bubble properties, temperature fluctuations and heat transfer coefficient in the riser have been determined. It has been found that the temperature fluctuations can be a quantitative tool to characterize the heat transport phenomena in the riser of the three-phase circulating fluidized bed. The heat transfer coefficient appears to be closely related to the Δ T-fluctuations and bubble properties in the riser. The heat transfer coefficient and bubble properties have been well correlated in terms of operating variables.