EXPERIMENTAL STUDY OF THE INTERACTION BETWEEN A BUBBLE AND A POROUS PLATE

Abstract

This paper aims to experimentally investigate the interaction between a bubble and a plate with multiple holes. The bubble is generated under the plate by underwater electric discharge method, and the top surface of the plate is flush with the water-air interface. In order to reveal the bubble dynamics and the droplets formation caused by bubble oscillation, the interaction process is recorded by high-speed photography. Similar to the interaction between bubble and plate with a single hole, there exist two jets, the primary slow jet and the secondary fast jet, caused by bubble expansion and collapse, respectively. The former starts to be pumped out as liquid columns and breaks up into fine droplets over time, while the latter erupts directly as droplets with more instability. As the distance between bubble and porous plate decreases, the speed of droplets increases and the velocity difference in droplets through different holes becomes greater. Besides, with the longer oscillation time the bubble is less likely to detach from the plate, and its maximum volume will be larger than expected. The effects of plate thickness and hole diameter on bubble dynamics and droplets formation are also investigated. Increasing the plate thickness and decreasing the hole diameter make the porous plate have a similar effect as the rigid wall. In this case, the bubble tends to migrate to the plate and inside the bubble, a jet toward the solid boundary will be generated. The amount of liquid being squeezed out through holes is reduced and the liquid columns are more likely to break up into sprays. In contrast, decreasing the plate thickness and increasing the hole diameter enhance the effect of free liquid on the bubble dynamics. Also, the efficiency of the oscillating bubble to pump liquids has increased.