A MECHANISTIC MODEL FOR PHASE HOLDUP PREDICTIONS IN A 3-PHASE FLUIDIZED-BED

A mechanistic model developed based on modification of the concept underlying the classical wake model (CWM), more specifically the generalized wake model, is presented to account for the phase holdup behavior in gas-liquid-solid fluidized beds. The CWM is characterized by two parameters, namely, the relative wake size and the relative solids content in the bubble-wake, and assumes the wake to be closed. Conventionally, one of these two parameters is calculated indirectly from the phase holdup data with an assumed value or a presumed empirical correlation for the other parameter. In addition to these two parameters, the present model takes into account the inherent physical behavior of the wake involving liquids and solids exchanges due to the vortex shedding and formation. Moreover, the relative wake size and relative solids content in the bubble-wake used in the model are obtained directly from the experiments or experimentally based correlations. Based on the present model, it is found that the predicted liquid holdup is fairly insensitive to the frequency of the vortex shedding and to the ascending velocity of the shed vortices. Thus, the liquid holdup prediction based on the present model is fairly close to that based on the generalized wake model.