Shape deformation and oscillation of particle-laden bubbles after pinch-off from a nozzle

Abstract

The rise of bubbles in liquid is a common phenomenon in chemical engineering applications. Bubble dynamics, however, are not fully understood, particularly at the early stages after bubbles are released from submerged nozzles, or when particles coat the bubble surface. In this work, a detailed investigation of microparticle-laden bubbles rising in water after being released from a nozzle was carried out to determine the influence of bubble surface coverage on the interface dynamics after pinch-off. The use of high-speed photography, at up to 25170 frames per second, allowed two regimes to be systematically investigated for the first time, i.e. an initial bubble shape deformation and shape oscillations. Surface pressure analysis shows that microparticles reduce the apparent surface tension of the interface by generating surface pressure during the initial bubble deformation. In contrast, during shape oscillations, little effect was observed on the period of the dominant harmonic, indicating that surface tension does not change during the oscillations. Harmonic analysis also showed that microparticles at bubble surfaces significantly increase the damping rate of the dominant harmonic, with a dependency on the bubble surface coverage. By quantifying the effect of particles on bubble dynamics, this work contributes to a better understanding of gas–liquid–solid reactors in which particle attachment plays a key role.