A method for consistent cavitation bubble generation at different voltages

Abstract

A study of the dynamics of a single cavitation bubble is fundamental for understanding a wide range of applications in science and engineering. Underwater electrical discharge is a widely used method for generating cavitation bubbles to study their inception, subsequent dynamics, and collapse. In this work, an existing underwater low-voltage discharge circuit for generating cavitation bubbles is improved further to get a wider range of maximum bubble radius. In this novel electric circuit design, the operating voltage can be varied (up to 420 V in steps of 60 V) by connecting a network of capacitors in different series-parallel combinations with the help of relay-based control. Therefore, this device can generate oscillating cavitation bubbles up to a maximum radius of 14 mm by adjusting the available discharge energy. A voltage sensor circuit is included in this design to measure the drop in voltage during the sparking event, and a correlation between the delivered energy and the potential energy of the bubble is established. The dependence of bubble radius on circuit resistance, electrode resistance, and electrode material is studied for the entire voltage range. A suitably rated semiconductor field effect transistor is used as a switch that enables the generation of bubbles of a consistent maximum radius and ensures the repeatability of the experiment. A high-speed imaging system is used to estimate the bubble radius and nucleation period, which are compared with the existing theoretical models based on empty cavity collapse. Results show that delaying the oxidation of electrodes with a protective layer influences the collapse phase and the average pressure inside the spark-generated bubble.