Career: Dynamics of coalescence and mixing during droplet impact on liquid films

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Many processes of industrial importance involve the impact of a liquid droplet on a liquid surface. Examples include inkjet printing, spray cooling, spray coating, and fuel injection in combustion engines. This CAREER award will use advanced experimental techniques and analytical methods to reveal the detailed dynamics of droplet impact with liquid surfaces from the sub-micron to millimeter scale. The goal of the project is to identify how ambient conditions and material properties influence droplet impact and fluid mixing following impact. The project will also provide venues for student engagement and outreach activities. High school students will participate in the research through UCSD’s ENLACE program. Undergraduates, especially first-generation college students, will be engaged in outreach activities sponsored by the UCSD rocket clubs. Graduate students will benefit from a new experiment based on the science explored in the project that will be developed for a graduate course.This CAREER project aims to investigate droplet impact on liquid surfaces and provide critical insights in assessing impact dynamics and mixing behavior. The study will involve many advanced optical measurements, such as imaging, interferometry, particle image velocimetry, and laser-induced fluorescence, all of which will be performed at high speed. Experiments will identify the microscopic physics associated with the evolution of an interfacial gas layer trapped between the droplet and the film, which controls the coalescence process. Then, the project will focus on the mixing of droplet liquid with the film immediately following coalescence and how mixing is affected by impact inertia, film geometry, molecular diffusion, and liquid properties. The results of the study will aid in the design of industrial applications mentioned above and will provide insight more broadly into other multiphase processes, including droplet-droplet and jet-jet interactions often relevant in propulsion, power generation, medical, bioengineering, and manufacturing applications.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.