Surface Bubbles: Thin Films & Interfacial Fluid Mechanics

Abstract

Bubbles play an important role in industrial as well as natural processes. In particular, bubbles at the surface of the ocean can create aerosol spray drops which are transported to the atmosphere and influence global-scale dynamics such as cloud condensation nucleii and radiation balance. As such, improved understanding of surface bubble processes, and in particular the physics of their spray production, is an important aspect of improving models of global-scale climate dynamics. This thesis focuses on three distinct processes which surface bubbles can undergo: coalescence where they join together, film drop production where liquid from the thin-film cap is fragmented into spray drops, and microplastic transport by jet drops arising from the bubble's cavity. Each thrust is driven primarily by laboratory experiments with numerical tools employed where useful. Coalescence of bubbles is one of the fundamental mechanisms by which the size distribution of bubbles on the surface of the ocean can change, the other being bursting. This work presents the first examination of surface bubble coalescence physics, and it is particularly important since coalescence of bubbles in the ocean is most likely to happen on the surface where they are attracted together. Subsequently, two mechanisms by which spray drops can be produced are examined. Film drops arise from the fragmentation of the thin-film liquid cap of the bubble, and while numerous studies have examined film drop, this work publishes the first extensive examination of their production across a wide range of conditions. Finaly, jet drops are examined for their ability to transport small particulate matter - such as microplastic - out of the bulk liquid. The work is comprised of experiments which determine the number of particles transported per bubble burst. This information is then used to construct a model to estimate the amount of microplastic being ejected from the ocean on a global scale which accounts for ocean conditions. The variability in microplastic concentration is explored to determine a range of possible annual microplastic ejection rates.