Measuring and modeling particle enrichment in jet drops from bursting bubbles

当气泡上升到水面并爆裂时，细菌和病毒等微粒可以从受污染的水源雾化，形成喷射液滴。这些喷射液滴中的细菌浓度可能高得惊人，比源头的浓度高1000倍。这种富集可能发生，因为气泡在上升过程中清除颗粒。如果是这样的话，富集程度应该取决于微粒在气泡破裂之前离气泡有多近。然而，仅仅基于这些想法的预测与现有的数据集不一致。该项目的目标是揭示流体动力学，它决定了包裹在这些液滴中的各种类型和大小的颗粒的富集因子。研究结果可能对与健康和环境有关的各种问题具有重要意义。具体来说，这项研究将导致对特定病原体在特定大小的喷射物中富集程度的机制理解。这些信息对于预测暴露于受污染水源的人的感染风险和确定适当的缓解战略至关重要。此外，病毒和其他来自海洋的颗粒在喷射液滴中的运输对云的形成有影响，这与全球气候模式有关。此外，其他海洋颗粒（如微塑料）的运输是一个重要的环境问题，了解颗粒富集对于估计空气-水界面的传输速率至关重要。该项目还将为幼儿教育教师和工程研究生提供机会，利用水滴和气泡作为途径，提高教育工作者和年轻学习者对STEM过程的可见度和可及性。几十年的研究探索了上升的气泡如何清除污染水源中的悬浮颗粒，并将颗粒与气泡一起带到水面。同样，重要的研究已经探索了气泡在破裂时如何产生喷射液滴，部分原因是这些喷射液滴中的颗粒可能对健康和环境产生影响。然而，在气泡破裂过程中，颗粒如何被输送到喷射液滴中，人们的理解有限。这种理解对于预测喷射液滴中观察到的浓度增强至关重要，也是本项目的目标。通过直接实验、数值模拟和适当量纲化的机制模型相结合，将对颗粒被封装的微观流体动力学进行研究。特别要注意的是那些可能被扫气带到地面的颗粒，但由于它们的大小、物理性质和位置而没有被封装。通过对封装过程进行建模，可以对实验不可行或有潜在危险的颗粒预测气溶胶液滴的浓缩程度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Particulates, such as bacteria and viruses, can be aerosolized from contaminated water sources when air bubbles rise to the surface of the water and pop, forming jet drops. The concentration of bacteria in these jet drops can be surprisingly high, up to 1000 times more concentrated than in the source. This enrichment may occur because the bubble scavenges particles as it rises. If so, the degree of enrichment should depend on how close particulates are to the bubble immediately before it pops. However, predictions based solely on these ideas are inconsistent with existing data sets. The goal of this project is to uncover the fluid dynamics that determines the enrichment factor for various types and sizes of particles that are encapsulated into these droplets. The results could be important to a variety of problems related to health and the environment. Specifically, the research will lead to a mechanistic understanding of the extent that a particular pathogen is enriched in a particular-sized jet drop. This information is critical to predicting the risk of infection to people exposed to contaminated water sources and to determining appropriate mitigating strategies. Furthermore, the transport of viruses and other marine-derived particles in jet drops has an impact on cloud formation, which is relevant to global climate models. Additionally, the transport of other marine particulates such as microplastics is an important environmental concern, and an understanding of particulate enrichment is critical to estimate transfer rates across the air-water interface. This project will also provide opportunities for early childhood education teachers and engineering graduate students to use drops and bubbles as a pathway to increase the visibility and accessibility of STEM processes to educators and young learners.Decades of research has explored how rising bubbles can scavenge suspended particulates in a contaminated water source and bring the particulates along with the bubble to the water surface. Similarly, significant research has explored how bubbles can create jet drops as they rupture, motivated in part by the impact that particles within these jet drops can have on health and environment. However, there is limited understanding of how particulates are transported into jet drops during the bubble rupture process. This understanding is critical to predict the enhanced concentrations observed in jet drops and is the objective of this project. Through a combination of direct experiments, numerical simulations, and appropriately dimensionalized mechanistic models, the microscale fluid dynamics by which particles are encapsulated will be investigated. Particular attention will be given to particles that may be brought to the surface by scavenging, but not encapsulated due to their size, physical properties, and location. By modeling the encapsulation process, the degree to which aerosol droplets are concentrated can be predicted for particulates for which experiments are unfeasible or potentially hazardous.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.