Effects of surfactant on quasi-static bubble growth from an orifice

The effects of surfactant on quasi-static bubble growth from an orifice of 2.0 mm in diameter were investigated by using a high-speed video camera and an image processing method. Triton X-100 was used for surfactant and its concentrations were set at 0.0, 0.1, 0.3, 0.5 and 1.0 mol/m(3). To obtain further knowledge of the bubble growth in the clean and contaminated systems, the flow fields around the bubbles were measured by using particle image velocimetry (PIV). The conclusions obtained are as follows: (1) the increase rate of the bubble aspect ratio in the contaminated system almost agrees with that in the clean system before reaching a specific bubble volume, and becomes larger after that, (2) as the surfactant concentration increases, the smallest contact angle increases and the bubble volume at the smallest contact angle decreases; furthermore, the bubble volume at the branch point of the contact angle between the clean and contaminated systems nearly agrees with that at the branch point of the aspect ratio, (3) the surfactant does not affect the flow fields around the growing bubbles in the experiment. (c) 2016 Elsevier B.V. All rights reserved.