Understanding gas-phase hydrodynamics in bubble columns: a convective model based on kinetic theory

Abstract

Bubble column hydrodynamics exhibit a bubbly flow regime at low superficial gas velocity and a churn turbulent regime at higher superficial gas velocity, except in small diameter columns where slugging is observed. A convective model developed previously is compared to dynamic gas disengagement (DGD) data. Theoretical disengagement curves calculated from the convective model bubble velocity distribution (at steady state) compare well to DGD curves at the transition point. Our analysis of DGD curves using the convective model indicates that in the churn turbulent regime, gas hold-up consists of a superposition of large bubbles on a transition point bubble velocity distribution. A kinetic model for gas-phase hydrodynamics capable of describing both the bubbly and churn turbulent flow regimes is proposed. Absolute bubble velocity distributions are calculated based on an ideal bubble velocity distribution and rules of bubble-bubble interaction. A transition zone is predicted by the model. Overall gas hold-up is predicted in the bubbly and churn turbulent flow regimes and the fraction of gas hold-up in the form of large bubbles is determined in the churn turbulent flow regime. The transition zone is in agreement with the literature and the large bubble fraction in the churn turbulent flow regime is well predicted by the model.