Mass transfer and chemical reactions in bubble swarms with dynamic interfaces



Detailed, high-resolution numerical simulations have been performed on the buoyancy-driven motion of deformable, chemically reacting bubbles for different operating conditions, that is, Weber, Morton, and Schmidt numbers. In our simulations different bubble shapes and types of bubble wakes were observed. The wake types range from a closed wake without recirculation, to a closed wake with recirculation, to an unsteady wake, leading to vortex-shedding wakes. Two different bubble-rise trajectories were observed for different conditions: straight and zigzag shaped. The mass-transfer rates and the yields and selectivities of liquid-phase chemical reactions were determined for each case. A detailed analysis of the results was carried out, relating the differences in chemical reaction efficiencies to the dynamics of each flow. Furthermore, to obtain a better understanding of the dynamics of the flows inside bubble swarms and their impact on chemical reactions, numerical simulations were performed of multiple bubbles rising in a swarm. Different bubble counts, geometric configurations, and size distributions were considered. Mass-transfer rates and chemical reaction selectivities were determined and a comparison is presented between the results for bubble swarms and single bubbles. It was shown that for mixing-sensitive reaction networks, the hydrodynamics of the bubble swarm may significantly impact the reaction selectivity. Furthermore, it was demonstrated that bubble swarm dynamics differ from the dynamics of single bubbles. © 2005 American Institute of Chemical Engineers AIChE J, 2005