Microbubble Oscillation on Localized Heat Source Affected by Dissolved Gases in Water

Recently, we demonstrated that the local heating of degassed water can generate water vapor microbubbles and induce a rapid flow around the bubble. Although flow generation involves the self-excited oscillation of bubbles at a local heating point, the conditions under which the bubbles oscillate are not fully understood. In this study, the dependence of microbubble size and oscillation frequency on the concentration of non-condensable gas in water was investigated. A continuous-wave laser beam was focused on a $\beta$-FeSi$_2$ thin film, and water was locally heated using the photothermal conversion properties of the film. The results showed that the lower the concentration of non-condensable gas dissolved in water, the smaller the bubble size and the higher the oscillation frequency. Furthermore, it was found that the bubbles oscillate when the amount of non-condensable gas absorbed by the bubbles, i.e., the bubble size, falls below a specific level. This study can provide a new understanding of the bubble oscillation mechanism and lead to the development of fluid control technology using bubbles.