Drift flux in gas—liquid—solid fluidized systems from the dynamics of bed collapse

Abstract

In the present study, the bubble drift velocity in three-phase systems operated in the dispersed bubble flow regime is considered. A theory is developed to account for the dynamic behavior of the collapse of a three-phase fluidized bed after a sudden stop of the gas and liquid flows. Based on this theory, the bubble drift velocity and drift flux are defined and their physical implications are presented. It is shown that the bubble rise velocity in a three-phase fluidized bed consists of two components: one is the sum of solid-free-based superficial velocities of the original steady state operation and the other is the bubble drift velocity. In the case of a three-phase fluidized bed, the bubble drift velocity is physically represented by the rise velocity of bubble swarm in the dynamic system modified by the solids holdup change due to bed collapse. In the case of a three-phase packed bed, the rise velocity of bubble swarm in the dynamic system directly represents the bubble drift velocity. Experiments for the dynamic of bed collapse of a three-phase fluidized system using 3.04-mm glass beads are conducted. Predictions for the dynamic behavior of bed collapse by the proposed theory agree very well with experimental measurements. Experiments of a single bubble rising in a liquid—solid fluidized bed and bubble swarm rising in a gas—liquid bubble column are also conducted to study the bubble motion in a three-phase fluidized bed under two extreme conditions. A unified correlation is obtained to correlate all the results for the bubble drift velocity in a three-phase fluidized bed as well as those under the two extreme conditions.