Measurement of Two Kinds of Granular Temperatures, Stresses, and Dispersion in Bubbling Beds

Abstract

A CCD camera technique was developed to measure instantaneous particle velocities in a thin bubbling bed for fluidization of 530 μm glass beads. The hydrodynamic velocities were computed by averaging the instantaneous velocities over the velocity space using the concepts of kinetic theory. Laminar-type kinetic stresses and granular temperatures were computed from the measurement of instantaneous velocities. Bubblelike granular temperatures were computed from the hydrodynamic velocities. The measured Reynolds normal stresses per unit bulk density in the vertical direction were 8 times larger than the measured Reynolds normal stresses per unit bulk density in the lateral direction because of higher velocity fluctuations for particles in the bubble-flow region. The sum of the measured shear stresses was equal to the pressure drop minus the weight of the bed of solids within experimental error. The restitution coefficients for 530 μm glass beads, estimated from the ratio of shear to normal stresses, are in the range of 0.99. The mixing in the bubbling and turbulent fluidized beds is due to laminarlike particle oscillations measured by the conventional granular temperature and due to bubblelike granular temperatures produced by the motion of bubbles. The bubblelike granular temperature is much larger than the particle granular temperature. In the center of the riser, the particle granular temperature was about 3 times larger than the Reynolds-like granular temperature. These observations are consistent with the literature of particle dispersion in bubbling beds, such as the early Ruckenstein analysis of homogeneous and bubbling beds.