Microbubble Generation by Hollow Ultrasonic Horn Using Longitudinal and Torsional Complex Oscillation

Abstract

A hollow ultrasonic horn can generate microbubbles by breaking down the gas-liquid interface with ultrasonic oscillation in various liquids, including not only water but also highly viscous and corrosive liquids. On the other hand, as the flow rate of the supplied gas increases, the ultrasonic waves do not sufficiently disturb the gas-liquid interface, resulting in the generation of many large bubbles. The purpose of this study is to improve the miniaturization performance of the hollow ultrasonic horn to suppress the generation of large bubbles at high flow rates. Therefore, we evaluated the conventional horn whose ultrasonic oscillation is only longitudinal oscillation and a complex oscillation horn with longitudinal and torsional oscillation. The process of bubble generation, dissolved oxygen concentration, and bubble diameter distribution were investigated. As a result, there was no significant change in the diameter of miniaturized microbubbles in each horn, but the complex oscillation succeeded in suppressing the frequency of generation of large bubbles and increasing the amount of microbubbles generated.