단일 기포 체인에서 발생하는 기포의 역학과 액체 상 난류에 대한 실험적 분석

Abstract

In the present study, the bubble dynamics and liquid-phase turbulence induced by single-bubble chain injected from a single nozzle have been experimentally investigated. Using a high-speed two-phase particle image velocimetry, measurements on the bubbles and liquid-phase velocity field are conducted in a transparent tank filled with water, while varying the gas flow rate from 0.01 to 0.65 cc/s. The tested bubble size ranges between 2.5-3.3 mm, and the corresponding bubble Reynolds number is 830-1120. As the gas flow rate increases, it is found that the global shape of bubble dispersion is enhanced and bubble rise velocity is dependent on the distance from the centerline. At the higher gas flow rate, the wake vortices of leading bubbles cause an irregular behavior of the following bubble such as enhancement of radial spreading and rising velocity. For the liquid phase, it is found that the jet-like liquid flow is generated, and the flow shows spreading and decaying of liquid velocity along the axial direction. Here, by measuring the velocity field of gas and liquid phases, an interaction between gas and liquid phases was found. First, the bubble rising velocity is enhanced by the surrounding liquid phase, resulting in decreasing trend as the distance from the centerline increases. Next, liquid flow induced by a bubble chain is influenced by bubble diameter, rising velocity, release frequency, and void distribution. Considering this, we try to provide a theoretical model to estimate the time-averaged vertical velocity of liquid-phase induced by a chain of bubbles.