The outbreak of a bubble may seem a trivial phenomenon that characterizes the summer games of children, but hides complex mechanisms that influence the diffusion of pollutants, contaminants and even infectious diseases through the generation of aerosol droplets. While the scientific community has deepened for decades this process in pure substances, the impact of contaminants on the dynamics of the explosion has remained surprisingly little studied. A new study from the University of Illinois has now filled this gap, developing a theoretical model that predicts how impurities modify the characteristics of the aerosol jets produced by contaminated bubbles.
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When a bubble rises to the surface due to the floating push, its surface is covered with the surrounding chemicals: microplastics, nanoplastics, biosurchant and even bacteria and viruses. At the time of the breakdown of the superficial capa mechanism is triggered for which surface waves concentrate and cause the expulsion of fluid in the form of jets, known as Worthington jets. This process distributes contaminants through fluid jets and resulting aerosol droplets, creating a particularly effective spread vehicle.
Professor Jie Feng, an expert in mechanical engineering at the University of the Urban-Champign Illinois, led the research team that developed this innovative theoretical approach. “Bubbles are commonly formed or are intentionally used in many natural and engineering contexts,” explains Feng. “This mechanism is essential to understand phenomena such as contaminants transported by air from oil spills and the spread of respiratory diseases”.
From theory to experimental practice
To study the phenomenon, the Feng laboratory has used a specialized system with a coaxial orifice that injects gas into the water to form bubbles, subsequently covering them with silicone oil. By varying the properties of the oil, the researchers were able to analyze the impact of its characteristics on the properties of jets by means of high -speed shooting. Zhengyu Yang, a graduate student in the Feng laboratory and the main author of the study, explained: “My research focused on the mechanics of fluids and on the environmental impacts related to the outbreak of the bubbles. We had already established the experimental skills necessary to generate high quality data on this problem”.
The results revealed that the size of the EXPULSE Aerosol droplets depends on three critical factors: the thickness of the oily layer, the viscosity of the oil and the surface tension. To explain this behavior mathematically, the researchers have introduced a new parameter that takes into account the presence of the oily layer, called “number of Ohnesorge revised”, with reference to the classic number of Ohnesorge that governs the dynamics of pure jets.
Applications in the real world
The practical implications of this research extend well beyond the academic field. In waste water treatment plants contaminated with viruses or bacteria, the bubbles formed by mechanical agitation rise by collecting microorganisms on their surfaces. When they reach the atmosphere and burst, they spray droplets containing these pathogens, creating significant environmental and safety risks in the areas surrounding contaminated aquatic environments.
Aerosol jets represent a hidden but powerful vehicle for the spread of contaminants
The research, published on Physical Review Letters and selected as Editors’ Suggestionoffers precious tools to understand and mitigate the air transmission of contaminants mediated by bubbles and droplets. “To fully make their potential, our next step is to consider the collective outbreak of the bubbles – studies on many bubbles that produce aerosol jets at the same time, which represents a more practical scenario in the real world”, anticipates Feng.
Towards new frontiers of research
The study represents a starting point for future wider research. The team hopes that the tools and knowledge acquired in this research will be widely applicable to clarify the mechanistic influence of a variety of contaminated interfaces on Multifase flows. The collaboration also involved Yang Liu of Tsinghua University, underlining the importance of international cooperation in advanced scientific research.
This discovery could revolutionize the understanding of how pollutants, microplastics and pathogenic agents spread through the atmosphere, providing the health and environmental authorities with more precise tools to predict and contain contamination. The developed methodological approach From the American team he opens new perspectives for the study of complex phenomena that involve contaminated interfaces, with potential applications in the medical, environmental and industrial fields.
