New description of fluidization regimes

Abstract

Two pressure probes and an intrusive bi-optical probe provide experimental data in the bubbling and turbulent regimes to improve our understanding of the bubbling to fast fluidization regimes transition. Pressure, voidage and bubbling properties assessment allows for new description of turbulent fluidization hydrodynamics. Appreciable changes in the hydrodynamics appear well below the transition criterion Uc determined based on pressure fluctuations: bubbles are fast bubbles below Uc, in bubble-emulsion equilibrium state at Uc, and then become slow bubbles for higher fluidizing velocity; the maximum of the total fluidizing gas fraction in the bubble-phase is reached below Uc and never exceeds 75-80 %. The fluidizing velocity at which major hydrodynamics modifications are observed is lower than Uc. This critical velocity is detected with pressure drop assessment or voidage fluctuations frequency analysis. Moreover, it can be theoretically calculated from the two-phase modeling correlations supplemented with a new criterion deduced from our experiments.