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.
Venturi channels taken as bubble generators own merits of simplicity in structure, high efficiency, and high reliability. A visualized investigation was carried out on bubble transportation and breakup in two small rectangular Venturi channels with the throat sizes of 1 mm × 1 mm and 1 mm × 2 mm, respectively. Experiments were conducted under ambient conditions with air and water as the working fluids. The experimental results indicate that bubble transportation and breakup in the Venturi channel with the throat size of 1 mm × 1 mm presents some different features compared with the other one: under the same average liquid velocity in the throat, bubbles own higher initial velocity than the average liquid velocity before entering the diverging section, and remain this trend till they are split; a binary breakup occurs to the bubbles prior to their final collapse in the recirculation region due to the jet flow in the backward of the bubbles. The bubble transportation and breakup in the Venturi channel with the throat size of 1 mm × 2 mm shows similar characteristics with that in a conventional Venturi channel. Overall, Venturi with smaller size presents a better performance in producing fine bubbles.
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