Characterization of Regime Transition in Fluidized Beds at High Velocities by Analysis of Vibration Signals

Abstract

Vibration measurement, as a reliable nonintrusive technique, was used to investigate the hydrodynamics of a gas–solid fluidized bed. The extensive experiments were carried out on a laboratory scale fluidized bed, operated under ambient conditions and various particle sizes of sand, aspect ratios, and superficial gas velocities. Pressure fluctuations and vibration signals were recorded at sample frequencies of 400 Hz and 65.6 kHz, respectively. The signals were processed using various techniques such as the standard deviation, Kolmogorov entropy, average cycle frequency, and power spectral density function. The results showed that the vibration technique is able to predict the regime transition from bubbling to turbulent fluidization conditions. It was shown that the transition from bubbling to turbulent can be determined from the variation of the standard deviation, Kolmogorov entropy, and average cycle frequency of vibration signals. However, the velocity can be determined only from the standard deviation of the pressure fluctuation. Other methods of analysis, applied to pressure fluctuations, predicted the transition between the macrostructure and the finer structure of the fluidized bed system, but not the transition velocity from bubbling to turbulent.