Rise velocities of single bubbles in a narrow channel between parallel flat plates

• Published in: International journal of multiphase flow 2019-02, Vol.111, p.285-293
• Main Authors: Hashida, Masaaki, Hayashi, Kosuke, Tomiyama, Akio
• Format: Article
• Language: English
• Subjects: Bubble lateral motion; Drag coefficient; Rise velocity; Two-dimensional bubble; Viscosity effect
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2018.09.015

•Shapes and velocities of bubbles in liquids between parallel plates are measured.•Effects of bubble lateral motion on rise velocity are clarified.•Effects of liquid viscosity on shapes, velocities and paths of bubbles are discussed.•Filella's empirical velocity correlation is supported by the force balance. Effects of the bubble lateral motion and the liquid viscosity, μL, on the rise velocity, VB, and the drag coefficient of a single bubble in a narrow channel were investigated. The gap thickness of the channel was 3 mm. The bubble diameter, dB, was from 7 to 20 mm. Clean water and glycerol–water solutions were used for the liquid phase. The μL ranged from 0.9 to 65.7 mPa s. Air was used for the gas phase. The conclusions obtained are as follows: (1) the bubble motion transits from zigzagging to rectilinear as dB increases and the transition abruptly takes place at a certain critical dB, which decreases with increasing μL, (2) the abrupt transition causes a stepwise increase in VB, (3) the curvature of the bubble nose in the rectilinear regime strongly affects VB, resulting in unavoidable scatter in VB data in low viscosity systems due to large shape oscillation, and (4) Filella's VB correlation for air-water systems is deducible from the force balance and applicable to high viscosity systems, provided that the model coefficient is tuned for each μL, implying that the drag coefficient can be expressed in terms of the Morton number and the gap-to-bubble diameter ratio.