Session2: Ports, Coastal Engineering and Management
Title: LABORATORY EXPERIMENTS OF BUBBLE FORMATIONS AND BEHAVIORS IN SURFACTANT SEAWATER
Takumi Nonaka, Yasunori Watanabe
Surfactant concentration in seawater affects heat and gas exchanges between atmosphere and ocean via formations of air-bubbles during wave-breaking process as surfactant modifies surface tension to define bubble size. However, this effect to dynamics of bubble flows has poorly understood. This paper presents the surfactant effects on geometric and kinematic features of bubble plumes and residual surface foams observed in laboratory experiments using backlit image measurements. We found the both bubble size distributions in surfactant water and seawater are well approximated by a lognormal distribution, while the bubbles in pure water deviate from the distribution. We also found analogous features in mean diameter, population and terminal velocity of bubbles in the surfactant and sea waters. The behaviors of coalescence and collapse of buoyant residual foams on a still water surface highly depend on the surfactant concentration. Our findings may contribute to understand mechanical processes of aeration and degassing in regional and seasonal variations of surfactant concentration depending on oceanic biological activity.