An investigation on the performance of a micro-scale Venturi bubble generator

Abstract

Venturi-type bubble generators exhibit a simple structure, high efficiency, low power consumption, and high reliability. An experimental study was conducted to evaluate the performance of a micro-scale Venturi channel as a bubble generator. In addition, the mechanisms dominating the bubble breakup were analyzed based on observations. With a liquid Reynolds number in the throat part of 0.7–1.2 × 104 and a void fraction below 0.1, the micro-scale Venturi-type bubble generator can produce micro-bubbles with average diameters of approximately 0.2–0.4 mm. Bubble breakups induced by shear stress, shear-off, and interfacial instability were observed in the experiments. The dominating bubble breakup type was multiple breakup arising from interfacial instability and eddy collisions. The recirculation process played a crucial role in the bubble deformation and prolonged the residence time of bubbles in the diverging section, thereby intensifying the energy transmission between the turbulent flow and bubbles. A negative aspect associated with the bubble generator was identified—a limitation of the void fraction to values below 0.1 had to be imposed on the micro-scale bubble generator because it would be very difficult for the bubble generator to produce microbubbles at high void fractions. The larger fragments from bubble breakups would escape the diverging section, thereby experiencing only a small influence from the turbulence flow.