Microbubbles Coalescence During Transport in Vertical Channel Flows

Large eddy simulation coupled to a Lagrangian bubble tracker, previously developed to study two-way coupled turbulent bubbly flows in channels, is extended to cover four-way coupling. The bubble tracker accounts for bubble collisions with a hard-sphere model and bubble coalescence using a film-drainage model. Upward and downward vertical channel flows of water at shear Reynolds numbers of 150 and 590 are examined, with air bubbles of diameter db = 220 μm dispersed within the flows. Turbulence is found to significantly impact the level of bubble interaction, increasing the number of collisions and coalescences, but at the same time also increasing the number of collisions that do not result in a coalescence event (coalescence efficiency). The different behaviour of the bubbles, and the impact it has on the turbulence field in the two flow configurations examined, also plays a major role in the coalescence process. The paper demonstrates the capabilities of the overall model for predicting coalescence in bubbly flows, and its ability to model flows of industrial relevance such as enhanced oil recovery, fermentation processes etc, the results from which are also of value in increasing our understanding of such flows