Applying air bubbles to techniques for sanitizing surfaces has been growing rapidly in recent years from complex industrial machines to kitchen appliances. Specifically, air bubbles are proposed as a sustainable solution for cleaning biological surfaces to reduce high rates of foodborne illnesses globally. In the first half of this talk, I will discuss the fundamental source of such cleaning effects by discussing the shear stress exerted on the surface when a bubble bounces, and then slides along a tilted substrate. I will then show how we carry out cleaning experiments on controlled biological surfaces systematically. Our experimental results on bacteria-coated surfaces reveal that the optimum cleaning happens for a tilted surface of ~20. To rationalize this finding, we use numerical analysis and scaling arguments to explain how shear stress is maximized at a mid-value of tilting angles. In the second half of the talk, I will introduce an interesting phenomenon where bubbles of certain size show a backflipping behavior when they collide with a tilted surface. I will explain why bubbles exhibit this counter-intuitive behavior through experimental observations and reduced mathematical modeling. I will then discuss how this backflipping behavior of bubbles can be leveraged to enhance cleaning. Finally, time permitting, I will briefly show how applying sonic waves to bubbles can also enhance cleaning by inducing an infinite bouncing mode in bubbles.
About the Speaker
Alireza “Navid” Hooshanginejad is a Hibbitt Postdoctoral Fellow in the Center for Fluid Mechanics at Brown University. Navid received his B.Sc. (2014) in Mechanical Engineering from Sharif University of Technology in Iran, and his Ph.D. (2020) in Mechanical Engineering from the University of Minnesota. He has held a visiting Research Associate position at Flatiron Institute (2017), and a postdoctoral position in Biological and Environmental Engineering Department at Cornell University (2020-2022), before joining his current position at Brown University. Navid is an experimentalist and an applied mathematician working in the area of fluid mechanics and soft matter with focus on biological systems, and the environment. His research interests include drops and bubbles, interfacial instabilities, pattern formation, and self-assembly using table-top experiments and mathematical modeling. Navid has been the recipient of the Graduate Teaching Fellowship from the University of Minnesota (2020), and the Best Poster Award from the Gordon Research Conference on Granular Matter (2022). Navid is currently serving on the APS DFD Executive Committee as the Early Career Member-at-Large.
Host: Professor Leonardo Chamorro