SUSPENSION VISCOSITY AND BUBBLE RISE VELOCITY IN LIQUID-SOLID FLUIDIZED-BEDS

The effective viscosity which characterizes the pseudo-homogeneous pro perty of the liquid-solid suspension in gas-liquid-solid fluidization is examined in light of the velocity of single bubbles rising through the suspension. Experiments conducted in this study cover a wide range of bubble diameters (2-23 mm) under high solids holdup (0.48-0.57) co nditions. The study reveals that the liquid-solid medium exhibits a ho mogeneous, Newtonian property at any given solids holdup when the bubb le diameters are greater than 12-17 mm. The effective viscosities obta ined in this study based on equivalency of the single bubble rise velo city in Newtonian media as well as those reported in the literature ar e found to follow the Mooney-type relationship for solids holdup depen dence. The two parameters underlying this relationship can be correlat ed as a function of the particle terminal velocity, particle shape and packed solids holdup. When the bubble diameters are smaller than 12-1 7 mm, the effective viscosity of the liquid-solid medium deviates from the viscosity of the corresponding Newtonian liquid. The deviation wh ich marks the reduction in the bubble rise velocity reflects a signifi cant close-range interaction between particles. In this bubble size ra nge, the liquid-solid medium exhibits a non-Newtonian property charact erized by shear-thinning behavior with flow index approximate to 1/2. (C) 1997 Elsevier Science Ltd.