Exploring the hydrodynamics of dense beds of Geldart B and D gas-fluidized particles through the analysis of capacitance probe signals

The hydrodynamics of Geldart B and D solids dense fluidized beds, of spherical/irregular morphology, have been characterized using capacitance probes at ambient temperature and 500 °C. A statistical approach applied to the time series of local bed voidage reveals, at specific experimental conditions, a characteristic bimodal distribution in the emulsion phase voidage: a more expanded, high-voidage, phase can be distinguished from a low-voidage phase with values close to minimum fluidization condition. Quantitative and qualitative differences among tested materials can be associated to different particles morphology. Emulsion phase voidages for the tested samples collapse on the same characteristic value once normalized with the voidages at incipient fluidization condition. The Richardson-Zaki equation proves to effectively correlate also in the bubbling fluidization regime the voidage and gas superficial velocity in the emulsion phase. The influence of hydrodynamics of fluidized bed dense phase on mass transfer in the emulsion phase is clearly highlighted.