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Venturi-type bubble generators own advantages of simplicity in structure, high efficiency, low power consumption, and high reliability, exhibiting a broad application potential in various fields. This work presents a literature review of recent progress in the research concerning Venturi-type bubble generators, with a focus on the performance evaluation, bubble transportation, and breakup mechanisms. Experimental studies employing flow visualization techniques have played an important role in exploring the bubble transportation and breakup phenomena, which is vitally necessary for clarifying the bubble breakup mechanisms and understanding the working principle and performance of a Venturi channel as a bubble generator. A summarization was carried out on both experimental and theoretical work concerning parameters influencing the bubble breakup and the performance of Venturi-type bubble generators. Based on the geometric parameter optimization combined with appropriate flow conditions, it is expected that Venturi-type bubble generators can produce bubbles with controllable size and concentration to satisfy the application requirements, while a further work is required to illustrate the interaction between the liquid and gas bubbles.

The bubble breakup mechanism in a venturi-type bubble generator is a hot research topic, and the bubble breakup mechanisms induced by the axial regional flow field characteristics has long been studied and debated. A coupled volume of fluid and large eddy simulation numerical simulation method was conducted within the OpenFOAM ® framework to track the two-phase interfaces and transient turbulence characteristics of the flow field in a venturi-type bubble generator. A turbulence inlet database was established to ensure the reliability of the numerical solution and the economy of the calculation. The results indicated that the bubble breakup induced by the axial regional flow field characteristics of the divergent section can be divided into a steady-state disturbed breakup pattern and an unsteady-state disturbed breakup pattern macroscopically, the latter playing a dominant role in generating fine bubbles. Furthermore, a series of typical bubble breakup processes were captured via a Lagrangian approach that showed that interfacial instability played an important role at each stage of bubble transport: Kelvin-Helmholtz instability caused bubbles to detach from the gas film during the steady-state disturbed breakup pattern, and Rayleigh-Taylor instability induced the deformation of detached bubbles in the unsteady-state disturbed region. Additionally, viscous shear force strengthened the interfacial instability in the binary breakup process, and turbulent fluctuations and collisions contributed to the shattering of defective bubbles. Moreover, a shearing-off process tended to occur in regions with small vorticity fluctuations, therefore playing a small role in creating large clusters of bubbles.

Microbubbles have been widely used in power, chemical, mining and petroleum applications to improve energy efficiency. The venture-type bubble generator can improve reaction efficiency in chemical engineering as an efficient bubble generation method. Studying the flow field and bubble bursting mechanism can enhance the bubble generation performance. The volume of fluid (VOF) multiphase flow model was used in the Open Field Operation and Manipulation (OpenFOAM) framework to study the deformation and fragmentation behaviour of a single bubble in a Quasi three-dimensional. The relationship between the mechanism of bubble breakup and the flow field in the diverging section of a Venturi-type bubble generator was revealed. The reasons for the uneven distribution of bubble size were analyzed and discussed. The numerical simulation result shows that the fragmentation of a single bubble injected by the converging section is more substantial than that injected by the throat in the axial direction. Bubble fragmentation occurs mainly in the diverging section. The bubble's trajectory is highly similar to the vortex trajectory of the diverging section. The size of sub-bubbles generated by single bubble fragmentation decreases with the diverging angle and liquid flow rate increase. The differential distribution of turbulent kinetic energy in the radial position directly leads to the uneven distribution of the bubble size of the broken bubbles. As the liquid Reynolds number increases, static and dynamic erosion breakup are more prominent. The size of the sub-bubbles is much smaller.