Measurement of solid and gas holdups in two-dimensional Three-Phase Fluidized Bed using ultrasound and imaging techniques

Abstract

In this present work, a two-dimensional column with width of 30 cm., thickness of 1.5 cm., and height of 113 cm was employed to investigate the hydrodynamics of Three-Phase Fluidized Bed (TPFB) system. From the experiments, it was found that both superficial liquid and gas velocities affect the behavior of gas bubbles and solid particles in the system. The effect of liquid flow rate was more significant than that of gas flow rate. From image processing analysis, the bubble size decreased when the superficial velocity of either liquid or gas phase increased. Within yeast suspension system, an increase in yeast concentration gave rise to the smaller bubble size. Using ultrasonic transmission, it was found that the larger particle could lead to the less signal transmitted through the bed to the receiver. The relationship between solid holdup and amplitude ratio was found to be exponential. An increase in superficial gas velocity resulted a decrease in the amplitude ratio which represented the higher solid holdup. Ultrasonic transmission technique was mainly applied for investigating distribution of solid particle in the bed while visualization technique with digital image processing was employed to measure bubble size distribution which is used for determining the local gas holdup.