Generation of Ultrafine Bubbles in Water by Repeated Pressurization and Depressurization

Abstract

Ultrafine bubbles (UFBs), which are smaller bubbles than 1 μm in diameter, have some unique properties and are being applied in various fields. It is necessary to develop the UFB generation methods more suitable for various applications and industries. The optimal equipment design and operating conditions should be clarified to obtain the required UFB number concentration. In this study, we developed a novel UFB generation method that repeats pressurization and depressurization operations in shaking container, utilizing the pressure dependence on gas solubility in water. Mean bubble size of the generated UFBs was around 90 nm and was constant regardless of operating conditions. UFB number concentration increased as the number of repetitions of the compression and decompression shaking operation increased. The generated UFBs were confirmed to be stable in water for a month. It was presumed in this study that the promotion of bubble nucleation and suppression of bubble growth caused with rapid solubility change due to the pressurization / depressurization with shaking operation produced more UFBs in water.