PIV investigation of the influence of wall wettability and distance on dynamic behavior of a rising bubble

Abstract

The rising behavior of a single bubble under the influence of wall wettability (3.39°, 67.24°, and 154.80°) and distance (initial distance: 0 mm, 5 mm, 10 mm, 15 mm, 20 mm, and 25 mm) is studied through experiments. The shape, rising velocity, and offset trajectory of bubbles are measured by a high-speed camera, the velocity field of water is recorded by the particle image velocimetry (PIV). The image is post-processed in numerical form, and the dynamic parameters such as Eötvös (Eo) and Reynolds (Re) number are analyzed. According to the different characteristics of bubble velocity and trajectory, the bubble rising can be divided into three stages: the initial stage, the early stage, and the regular stage. In the initial stage, the bubble velocity increases; in the early stage, the bubble velocity fluctuates at a fixed frequency for two cycles, and in the regular stage, the bubble swings and rises. In addition, wall wettability has a strong impact on bubbles but is limited to a small range, while the distance is opposite. When the distance is 0 mm, the super-hydrophilic surface maximizes the bubble's disturbance to the water and forms a unique relationship between the offset trajectory and the Eo number: the offset trajectory increases with the increase of the Eo number. However, the super-hydrophobic wall makes the bubble hardly disturbs the water. The influence of wettability disappears when the distance exceeds 5 mm. The influence of bubble-wall distance shows periodicity with distance in this paper's experiment conditions. When the distance is an odd multiple of 5 mm, an abnormal peak occurs in the bubble velocity fluctuation, but when the distance is an even multiple of 5 mm, the offset trajectory decreases with the increase of the Eo number.