Time-series analysis of the characteristic pressure fluctuations in a conical fluidized bed with negative pressure

Abstract

The negative pressure conical fluidized bed is widely used in the pharmaceutical industry. In this study, experiments based on the negative pressure conical fluidized bed are carried out by changing the material mass and particle size. The pressure fluctuation signals are analyzed by the time and the frequency domain methods. A method for absolutely characterizing the degree of the energy concentration at the main frequency is proposed, where the calculation is to divide the original power spectrum by the average signal power. A phenomenon where the gas velocity curve temporarily stops growing is observed when the material mass is light, and the particle size is small. The standard deviation and kurtosis both rapidly change at the minimum fluidization velocity and thus can be used to determine the flow regime, and the variation rule of the kurtosis is independent of both the material mass and particle size. In the initial fluidization stage, the dominant pressure signal comes from the material movement; with the increase in the gas velocity, the power of a 2.5 Hz signal continues to increase. A method of dividing the main frequency by the average cycle frequency can conveniently determine the fluidized state, and a novel concept called stable fluidized zone proposed in this paper can be obtained. Controlling the gas velocity within the stable fluidized zone ensures that the fluidized bed consistently remains in a stable fluidized state.