Hydrodynamic transition from fixed to fully fluidized beds for three-phase inverse fluidization

Abstract

Hydrodynamic transition experiments, involving both visual observations and pressure measurements, were performed using a 127-mm diameter Plexiglas column for threephase inverse fluidized beds of 5.8-mm polyethylene spheres. Observations of interest not hitherto reported include: (1) A marked hysteresis effect (even when starting from a loose-packed condition) between inverse fluidization and defluidization which disappears when a wetting agent is added to the downflowing water. (2) An initially abrupt decrease of the minimum fluidization voidage, єemf, followed by a gradual rise of єemf with increasing superficial gas velocity, Ug. (3) Lower values of emf for three-phase systems than for the corresponding two-phase (liquid-solid) fluidized beds because local agitation by the gas bubbles causes bed compaction near the minimum liquid fluidization velocity, Ulmf. (4) Ulmf vs. Ug curves which, though they always show Ulmf decreasing as Ug increases, sometimes display concave-downward, sometimes concaveupward and sometimes S-shaped behavior.