Bubble and bubble wake characteristics in a gas-liquid-solid fluidized bed

The hydrodynamics of a gas-liquid-solid fluidized bed were investigated by examining the behavior of bubbles and bubble wakes. Both single bubbles rising in a liquid-solid fluidized bed and individual bubbles in freely-bubbling beds were studied.; A light transmittance technique involving a dual optical fiber probe was used to measure the local solids holdup in a three-dimensional gas-liquid-solid fluidized bed. The bubble could be clearly identified in the same signal, thus permitting the simultaneous determination of the local solids holdup profile in the wake of a single bubble and the rise velocity and chord length of the bubble.; The solid holdup behavior was studied in the wake of single bubbles rising in a liquid-solid fluidized bed for different liquid velocities, particle sizes, and bubble sizes. The wake solids holdup was found to decrease with decreasing mean solids holdup in the bed, to be essentially independent of the bubble Reynolds number over the range investigated in this study (4000 {dollar}<{dollar} Re{dollar}sb{lcub}rm b{rcub}{dollar} {dollar}<{dollar} 8000), and to decrease with increasing particle size.; In freely bubbling beds at low gas holdups ({dollar}varepsilonsb{lcub}rm g{rcub}{dollar} {dollar}<{dollar} 0.03), both the solids holdup in the wake and the particulate phase solids holdup were measured. The light transmittance probe developed for the single bubble system was also used for these measurements. Axial variations in the particulate solids holdup indicated that the relative wake solids holdup increased with axial distance from the distributor. The best agreement between the single bubble measurements and the measurements in the freely bubbling bed occurred in the bubble formation region.; And finally, a simple model of the bubble wake was developed based on equations available in the literature for a spherical vortex to predict both the wake size and the relative wake solids holdup. The predictions showed good agreement with the experimentally observed values.