Flow Structure of the Solids in a Three-Dimensional Liquid Fluidized Bed

Abstract

The motion of solids in a cylindrical liquid fluidized bed was experimentally characterized by means of a noninvasive radioactive particle tracking technique (RPT) for two monosized bed inventories, spherical glass beads (3 mm GB, density = 2,500 kg/m{sup 3}) and nonspherical poly-(vinyl chloride) particles (5.5 mm PVC, density = 1,300 kg/m{sup 3}). RPT-monitoring of a single radioactive solid tracer mimicking faithfully the characteristics of the solids revealed the detailed solids flow features by determining the tracer instantaneous 3-D Lagrangian trajectory and then its local instantaneous velocities. Transverse solids dispersion coefficients were an order of magnitude lower than their axial counterpart. Time, longitudinal, and circumferential averaging of local velocities in the fully developed region of the fluidized bed revealed a weak gulf streaming characterized by axial velocities positive (respectively negative) in the core and negative (respectively positive) near the vessel walls for the GBs (respectively for the PVCs). The measured mean circumferential ensemble-averaged radial velocity was essentially zero in the fully developed region. The solids flow turbulence field was anisotropic, but the less dense the particles, the closer to isotropy was the solids flow. Computed shear stress profiles showed that PVC particles exhibited a higher shear stress than GB particles. Themore » dynamic solids flow structure inside a 3-D liquid fluidized bed can be viewed as a core-annulus structure with axially-dispersed plug-flow and radial dispersion in each of the upward and downward zones.« less