Transition Velocity and Bed Expansion of Two-Phase (Liquid-Solid) Fluidization Systems

Hydrodynamic transition experiments for two-phase (liquid-solid), both upward and downward, liquid flow systems were performed in a 127-mm diameter column. The particles were 3.2-mm polymer (1,280kg/m³), 5.8-mm polyethylene (910, 930, 946 kg/m³), 5.5-mm polystyrene (1,021 kg/m³) and 6.0-mm glass (2,230 kg/m³) spheres, with water, aqueous glycerol solution and silicone oil as liquids. The dimensionless pressure gradient increases initially with increasing liquid velocity, but decreases gradually with increasing liquid velocity beyond U_lmf due to bed expansion. The non-dimensionalized pressure gradient using the liquid/solid mixture density increases with increasing liquid velocity and then reaches a constant value close to unity beyond U_lmf. The minimum fluidization Reynolds number for liquid-solid system increases with increasing Archimedes number including both heavier and lighter than the density of the liquid phase. U_lmf should be the same for both upward and downward fluidization systems since the Ergun equation is based on the main assumption that drag force of the superficial liquid velocity, U_lmf, is equal to the net difference between gravitational and buoyancy forces.