Bubble Interactions With Free Interfaces

Bubble collisions with other bubbles, particles or interfaces are very important in a variety of mass transfer applications. The rise of a buoyant bubble and its interaction with a free liquid surface was experimentally investigated using a Time-Resolved DPIV system. The results are presented as functions of bubble size, and surfactant concentration of the fluid medium. It is shown that the presence of a surfactant significantly affects the approach and collision characteristics of the bubble. The addition of a surfactant changes the viscous forces around the bubble due to the adsorption coverage of the surfactant at the bubble-fluid interface. A bubble traveling through a surfactant solution (1e-3 M Sodium Dodecyl Sulfate) did not exhibit bouncing behavior regardless of its size. The flow is characterized by a vortex ring trailing the bubble during the approach stage. After impact, the vortex ring slowly diffuses away parallel to the wall and dissipates. In contrast a smaller (1.1 mm) bubble in pure water rebounded from the free surface three distinct times. The rebounding exhibits complex vortex interactions, and the vortices tend to dissipate more quickly than in the no-rebound case. Vortex dynamics play an important role in determining the energy dissipation. Comparisons with other computational and experimental works are combined with the present study to more accurately describe the dynamics of the bubble rebound.