Numerical Simulation on the Motion and Breakup Characteristics of a Single Bubble in a Venturi Channel

The Venturi channel is a dominant part of Venturi-type microbubble generator. In the current study, a three-dimensional virtual bubble was patched to the steady flow of a Venturi channel by the volume of fluid model coupled with the level set method. The bubble roundness and motion trajectory were defined to describe the motion and deformation process, while the gas-liquid interfacial area was indicated to evaluate the breakup characteristics. The numerical simulation model was then validated through a visualization experiment. The motion trajectory and roundness of the patched bubble were sensitively affected by the gravity direction. When the gravity direction was vertical to the liquid flow, the bubble experienced more violent deformation than that of the horizontal direction. Then, the bubble experienced a serious breakup once entering the divergent section, and the breakup pattern was divided into binary breakup mode and multiple breakup mode owing to the bubble coordinate position. Through force analysis, the axial pressure gradient force, which contributed to the binary breakup mode, mainly existed in the central region, and the radial shearing force, which contributed to multiple breakup mode, existed in the sidewall region. Considering the positive correlation between the gas-liquid interfacial area and the daughter bubble size, the gas-liquid interfacial area ratio delta was proposed. The functional relationship between delta and the liquid-phase Reynolds number Re or the divergent angle beta was typical logarithmic, respectively. The delta value increased with the increase of Re and beta, whereas the correlation of Re to delta was much more significant.