Bubble breakup in a swirl-venturi microbubble generator

We present a novel swirl-venturi microbubble generator enabled by tangential inlets in this work, and employ a high-speed camera to obtain breakup phenomena of a single bubble in both the venturi microbubble generator and the swirl-venturi microbubble generator. We observe three different breakup patterns (i.e., tensile breakup, dynamic erosive breakup, and static erosive breakup) in swirl-venturi microbubble generator, while in venturi microbubble generator only tensile breakup exists. Furthermore, both tensile breakup and dynamic erosive breakup appear less frequently with increasing liquid velocity in the swirl-venturi microbubble generator, while static erosive breakup tends to dominate. CFD simulations of liquid flow field show the existence of an apparent vortex region near the wall of the diverging section in the SVMG, which is the essential cause of the erosive breakup of bubbles. Statistical analysis results reveal that the location of bubble initial breakup in the venturi microbubble generator is close to the central axis, while in swirl-venturi microbubble generator it is near the wall and more concentrated. The swirl-venturi microbubble generator performs better than conventional venturi microbubble generators, providing a new idea for strengthening bubble breakup under high gas-liquid ratios.