A Study of Surfactant Effects on the Liquid-Phase Motion around a Zigzagging Ascent Bubble Using Recursive Cross Correlation PIV

T. Saito, K. Sakakibara, Y. Miyamoto, and M. Yamada. Graduate School of Engineering, Shizuoka University,

3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8561, Japan

*Email: ttsaito@ipc.shizuoka.ac.jp

ABSTRACT

The velocity field around a zigzagging ascent bubble has a wide dynamic range. It is hard to precisely measure such velocity field via conventional type of PIV. In this study, to overcome this difficulty the authors employed recursive cross-correlation algorithm and a high-speed video camera. The analysis code of a newly developed PIV system showed the high performance in measuring velocities of wide dynamic range. At first, the authors demonstrate the performance of the recursive cross-correlation PIV algorithm compared with the results obtained by conventional type of PIV algorithm using the standard PIV images of wide dynamic range presented by The Visualization Society of Japan.

Second, the developed system was applied to measure velocity field around a zigzagging ascent bubble, and its surface motion simultaneously. Third, surfactant effects on the surrounding liquid motion (i.e. the intensity of the vorticity, the size of the vorticity and the structure of a hairpin-like vortex) were discussed, as well as those on the centre-of-gravity and the surface motion of the bubble. In this study, a very small amount of surfactant (1-pentanol) solutions were examined. Although the bulk surface tension was almost the same as that of purified water, the bubble motion and the surrounding liquid motion in the solutions (i.e. contaminated system) were very different from those in purified water (i.e. purified system). A critical concentration of a surfactant was found out. At the critical concentration, the intensity and size of the vorticity becomes the largest. From the consideration coupling the asymmetric surface motion of the bubble and the surrounding liquid motion, it has been found out that the Marangoni stress owing to a concentration gradient of the adsorbed surfactant on the bubble surface plays a great role.

Keywords PIV, recursive cross correlation algorithm, surfactant effect, bubble, liquid-phase motion