Bubbly flow in an airlift column: a CFD study

BACKGROUND: Multiphase CFD (Computational Fluid Dynamics) simulation is a valuable tool in chemical and bioprocess engineering that is particularly useful to study reactor concepts and their scale-up from laboratory to production scale. Simulations of bubbly flows up to industrial dimensions are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, for practical applications suitable closure models are needed which describe the physics on the scale of individual bubbles or groups thereof. The quest for such models with a broad range of applicability allowing predictive simulations is an ongoing venture.
RESULTS: A set of closure relations for the fluid dynamics of bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions. This model has been successfully validated for bubbly flows in pipes and bubble columns. Here it is applied to the case of an internal loop airlift column which is frequently used in biotechnological processes.
CONCLUSION: Within the limitations of the experimental data available for comparison, the closures are found applicable to this case as well. Further development should account for the polydisperse nature of the flow. To this end reliable measurements of bubble size distribution are needed.