Condensation of vapor bubbles in a subcooled liquid is known to influence heat transfer and pressure oscillation in subcooled boiling and direct contact condensation. This study reviews the published literature concerning interfacial heat transfer and bubble dynamics in the process of bubble condensation. The correlations for bubble condensation are analyzed and evaluated with a database covering a wide range of Reynolds, Jacob, and Prandtl numbers. Then, the investigations addressing bubble dynamics are reviewed, which focus on the bubble condensation patterns, motion, collapse, and the pressure oscillations induced by bubble condensation, as well as the effect of noncondensable gas and field. Despite the extensive experiments of bubble condensation available in the literature, it is shown that there is still a shortage of investigation focused on the variation of thermal boundary layer and turbulence formed near the bubble at the micro-scale, which could help to develop the prediction method of bubble condensation in the future. The transportation of noncondensable gas inside the mixture bubble and effect of capillary waves formed on the bubble surface on the actual vapor-liquid contact area and thermal boundary are also suggested to be further investigated to gain the thorough understanding of the bubble condensation process.

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.