In my research group, we aim to gain a detailed understanding of the coupling of fluid dynamics, heat transfer, and phase change in select multi-phase systems, with a primary emphasis on droplets. In this presentation, I will introduce two projects that study the interaction between droplets and engineered surfaces in the presence of liquid-vapor phase change.
I will start by discussing our recent advances during droplet impact on heated surfaces, where we can differentiate between three different regimes: low-Weber number impact on smooth hydrophobic surfaces and impact on wettability-patterned surfaces, both in the film evaporation regime, and impact on a millimetric post in the nucleate boiling and Leidenfrost regimes. Using high-speed infrared (IR) imaging, we are able to analyze temperature and heat flux distributions in space and time. I will show that for the lower-temperature impact scenarios, conduction heat transfer dominates over evaporation, irrespective of droplet dynamics. For the high-temperature impact, the metal post structure alters droplet dynamics, increases the dynamic Leidenfrost temperature, and enhances the cooling performance on inclines surfaces.
In the second part, I will introduce our work on condensation and droplet dynamics on lubricant-infused surfaces (LISs). I will introduce two kinds of droplet (self-)propulsion: purely capillary-driven for thinner oil films, and capillary and shear driven for thicker oil films. I will show that under non-isothermal conditions (as present during condensation), Marangoni convection cells originate within the oil meniscus that can counter-act capillary attraction forces and lead to small droplets surprisingly descending the meniscus. My presentation will end by summarizing how these findings influence condensation heat transfer rates and introduce some unresolved questions.
About the Speaker
Dr. Patricia (Patty) Weisensee is an Assistant Professor of Mechanical Engineering and Materials Science at Washington University in St. Louis (WashU). She earned her PhD in Mechanical Engineering from the University of Illinois at Urbana-Champaign in 2016 (working with Bill King and Nenad Miljkovic). She received a Diplom-Ingenieur in Mechanical Engineering from TU Munich in 2013, and also holds a M.S. in Materials Sciences from the University of Illinois at Urbana-Champaign (2011; with David Cahill). At WashU, Patty leads the Thermal Fluids Research Group, which focuses on understanding the interplay of fluid dynamics and heat transfer of droplets and other multi-phase systems, with applications in thermal management, water harvesting, metal additive manufacturing, and droplet interactions with natural and engineered systems. To fundamentally study these thermal-fluidic interactions, her group combines multiple experimental techniques, such as high-speed optical and infrared (IR) imaging, interferometry, confocal fluorescence microscopy, and conventional heat transfer measurements. Patty is a recipient of the NSF CAREER Award, the NASA Early Career Faculty Award, the 2014 Siemens Energy Award, the 2020 ASME ICNMM Outstanding Early Investigator Award, as well as the 2020 Emerson Excellence in Teaching award. She is also an alumna of the German National Academic Foundation (“Studienstiftung des deutschen Volkes”).
Host: Prof. Nenad Miljkovic