油を塗布したガラス表面近傍の超音波キャビテーション気泡の可視化実験

抄録

Low-frequency underwater ultrasound is conventionally used to degrease metallic parts. It is important to reveal its cleaning mechanism in order to achieve more efficient cleaning for practical purposes. In this study, we set up a simple ultrasonic cleaning test and optically visualize acoustic cavitation bubbles. Glass plates on which an oil drop is deposited are used as a cleaning sample. The sample is soaked in a water container and subjected to 28-kHz underwater ultrasound. The ultrasound-induced cavitation bubbles near the glass surface are recorded by a high-speed camera. It is observed that cavitation bubbles nucleate preferentially in the water (not in the more viscous oil) and subsequently penetrate into the oil, perhaps, due to Bjerknes force. The visualization suggests that the dynamics of bubble clouds in the oil play an important role in degreasing.