Liquid pressure fluctuations around a needle during bubble departures

The bubble–bubble interaction and bubble–needle interaction are usually caused by liquid flow in the needle or the needle’s neighborhood. Moreover, nonlinear changes in the liquid’s velocity and pressure can lead to chaotic bubble departures. In the present paper, the liquid pressure changes in the needle’s neighborhood were experimentally and numerically investigated. In the experiment, bubbles were generated from a brass needle into distilled water. A second needle was placed at a distance of 1.5 mm from the needle which was used to generate the bubble and was used to measure the changes of liquid pressure during successive stages of bubble departures. It was shown that, during the bubble waiting time, the liquid pressure in the needle’s neighborhood fluctuates slightly. Significant changes in the liquid’s pressure were observed during the bubble growth stage. The influence of liquid pressure and liquid velocity above the needle on the bubble growing stage and bubble waiting time was discussed.