Microbubble has characteristics of large surface area to unit volume and small buoyancy. We propose an effective technique to generate tiny bubbles less than 200 μm diameter utilizing a venturi tube at high void fraction. The mechanism of bubble breakup in the venturi tube is elucidated that the bubbles expanded after passing through the throat and then shrank rapidly. The tiny bubbles are generated due to the surface instability of shrinking bubbles. The effect of bubble diameter and plume structure on mass transfer efficiency in bubble plumes and columns are investigated numerically. In order to capture the detailed plume structure, the interaction between liquid and bubbles is treated by a two-way coupling Eulerian-Lagrangian method. The gas transfer from bubbles to liquid is computed by modeling the mass transfer rate of individual bubbles. The numerical results show that the dissolution efficiency changes rapidly when the initial bubble size reaches certain value. The effect of bubble-induced liquid velocity on the residence time of microbubbles increases with the decrease of initial bubble diameters, and also increases with the reduction of initial water depth. By comparing the concentrated and uniform bubble injections, the results suggest that the uniform injection provides much better mass transfer efficiency becasue the circulation of liquid induced by bubble is greatly suppressed.
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