Simulation study on the phase holdup characteristics of the gas-liquid-solid mini-fluidized beds with bubbling flow

Previous simulations of three-phase fluidization systems based on the Euler-Lagrange approach have made progress in the studies of bubble and suspension dynamics. However, for guiding the operation and design of reactors, it is obviously more practical to obtain the phase holdup characteristics under the steady state. In this study, the hydrodynamic simulations on the gas-liquid-solid mini-fluidized beds (GLS-mFBs) were performed from the initial introduction of bubbling flow to the steady three-phase fluidization using the coupling model of volume of fluid (VOF) and discrete element method (DEM). After the initial process of bubbling flow accompanied by redistribution of phase holdups, i.e., the contraction of fluidized bed, the steady state of the GLS-mFB was achieved and maintained by the interactions between bubbles and fluidized bed. The axial and radial profiles of phase holdups in the steady GLS-mFBs, which is difficult to measure through experiments, are obtained and discussed. It is found that the suspension resistance against the rising bubbles is strengthened by the wall confining effect arising from the shrinkage of bubble-wall gap under smaller column diameter, and the phase holdup characteristics and bubble dynamics are investigated and explained by this effect. The bubble wake, which plays an important role in the momentum exchange between bubbles and suspension, is analyzed in terms of formation mechanism and size changes. It is proved that the VOF-DEM simulation is an effective method to predict the phase holdups of the GLS-mFBs and explain the underlying hydrodynamic mechanism.

Automated summary

The study conducted hydrodynamic simulations of gas-liquid-solid mini-fluidized beds using the VOF-DEM coupling model, achieving steady state flow and obtaining axial and radial profiles of phase holdups. The simulation proved effective in predicting phase holdups and explaining hydrodynamic mechanisms.