A Single Bubble 3D Motion in Dilute Surfactant Solution : 1st Report, Relation between Surfactant Concentration and 3D Motion(Fluids Engineering)

Abstract

To investigate surfactant effects on path instability of a single bubble, measurements of 3D trajectories, velocities, and aspect rations are carried out with a tank of 1.0m height filled with super purified water and a small amount of surfactant using two high-speed digital cameras. The experimental parameter is the concentration of 1-Pentanol (surfactant) which controls surface slip conditions of the bubble from free-slip to no-slip. The bubble size of 2.0±0.1mm is chosen to avoid shape oscillations. Our results of 3D motions in free-slip, no-slip and intermediate slip conditions agree with previous results. When bubble rise velocity is decided by slip condition, the trajectory is also decided. It indicates that the slip condition decides not only the drag force but also the wake structure. The maximum amplitude of the horizontal projection of the spiral motion is 4.7 times as large as the minimum one and- corresponds not to the maximum rise velocity but to the maximum horizontal velocity. As a result of the comparison with simple models, the mechanism of the trajectory change by surfactant is explained by effects of drag force and the direction of motion affected by non-axisymmetric wake structure.