Measuring and modeling particle enrichment in jet drops from bursting bubbles

当气泡上升到水面并破裂时，受污染的水源中的微粒，如细菌和病毒，可以被雾化，形成喷射水滴。这些喷射液滴中的细菌浓度可能会令人惊讶地高，比源头中的浓度高出1000倍。这种浓缩的发生可能是因为气泡上升时会清除颗粒。如果是这样的话，浓缩的程度应该取决于气泡破裂前的颗粒距离有多近。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，该流体动力学决定了包裹在这些液滴中的各种类型和大小的颗粒的浓缩系数。这一结果可能对与健康和环境有关的各种问题具有重要意义。具体地说，这项研究将从机理上理解特定病原体在特定大小的喷射液滴中的浓缩程度。这些信息对于预测暴露在受污染水源下的人的感染风险和确定适当的缓解策略至关重要。此外，病毒和其他海洋衍生颗粒在喷流水滴中的传输对云的形成有影响，这与全球气候模型有关。此外，微塑料等其他海洋颗粒物的迁移是一个重要的环境问题，了解颗粒物浓缩对于估计空气-水界面的迁移速率至关重要。该项目还将为幼儿教育教师和工程学研究生提供机会，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过程的可见性和可及性。数十项研究探索了上升的气泡如何清除受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，重要的研究探索了气泡在破裂时如何产生喷滴，部分动机是这些喷滴中的颗粒可能对健康和环境造成的影响。然而，人们对气泡破裂过程中颗粒是如何输送到喷射液滴中的了解有限。这一理解对于预测在喷射液滴中观察到的增强浓度是至关重要的，也是本项目的目标。通过直接实验、数值模拟和适当维化的力学模型相结合，将研究包裹颗粒的微尺度流体动力学。将特别注意可能通过清扫而带到表面的颗粒，但由于它们的大小、物理性质和位置而没有被包裹。通过模拟封装过程，可以对实验不可行或潜在危险的颗粒物预测气溶胶液滴的浓缩程度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.