Characterization of gas fluidized beds of group C, A and B particles based on pressure fluctuations

Pressure fluctuation data were obtained with a quick response transducer at a sampling frequency of 100 Hz for periods of 100 s (i.e. 10,000 points) in order to characterize the gas-solid flow behaviour of fluidized beds of six powders. For beds of Geldart group B and group A particles, the occurrence and movement of bubbles caused vigourous pressure fluctuations of relatively large scale and weak dominant frequency. For beds of group C particles, on the other hand, pressure fluctuations were significantly smaller in scale and exhibited large dominant frequencies, with no clear formation of bubbles. The standard deviation of pressure fluctuations was markedly higher for the group A particles than for the group C powders. Group C particles could be characterized by gas voids and channels which exhibit periodic behavior, while beds of group A and B particles behaved in a less periodic manner and were dominated by more random and intensive bubble motion. Chaotic time series analysis was carried out for the six different species of particles. The Hurst exponent demonstrated differences between the three different powder groups. The two-phase character of gas-solids flow was more distinguishable for the group B and A powders than for the group C powders.