Air bubbles in liquids have complex interactions with their surroundings. A rising bubble not only mixes the surrounding fluid but also collects suspended particles such as bacteria or microplastics on its interface, transporting them to the liquid surface. When a bubble bursts, it releases droplets that carry sea salt, microorganisms, and chemicals into the air, affecting both human health and the climate. Through experiments and theory, this dissertation studies the underlying mechanisms behind bubble-mediated biofouling prevention, air-sea particle transport, and sea spray formation.
Our first study examines the relationship between the flow fields created by rising bubbles and biofouling prevention on a submerged surface. Bubble aeration is a method for preventing biofouling organisms, such as barnacles, from growing on a surface without using environmentally harmful chemicals. We identify the critical flow characteristics of periodically rising bubbles that correlate with the prevention of multi-species biofouling over a seven-week period, offering a potential framework for studying and comparing flow fields that successfully inhibit biofouling.
Our next study investigates how small bubbles concentrate particles adhered to the bubble interface, such as plastics or microorganisms, into highly-contaminated droplets during the bursting process. We reexamine the assumption that only particles small enough to fit within a thin microlayer around the bubble can be transported into the influential top jet drop, and demonstrate that larger particles can also be transported and exhibit higher enrichment levels than predicted. We combine experiments and theory to develop an analytical model estimating the expected enrichment based on the bubble size, particle size, and particle position on the bubble.
We proceed by focusing on plastic particle transfer into the atmosphere via bursting bubbles from breaking ocean waves. Existing estimates of micro- and nanoplastic transport through this pathway have large uncertainties due to limited detection techniques and studies. We develop a modeling framework that examines the size-dependent transport of hydrophilic and hydrophobic plastic particles, revealing the dominance of jet drops over film drops and the potential for nanometer-sized plastics to become highly concentrated in the smallest drops.
Finally, we explore the role of salinity on the bursting bubble production of submicron drops, which are critical to cloud formation and other atmospheric processes. It is well-known that bubbles bursting in saltier water will produce more submicron drops. However, previous studies have attributed this trend to the suppression of bubble coalescence with higher salinity, leading to more numerous bubbles and consequently more drops. We demonstrate that submicron drop production increases with salinity, even when using a salt that does not affect bubble coalescence behavior. This finding implies that salinity has a systematic effect on the physics of submicron drop formation, even at the scale of a single bubble.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/46656 |
| Date | 30 August 2023 |
| Creators | Dubitsky, Lena |
| Contributors | Bird, James C. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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