Guest Speaker: Dr WANG Zhenying
Assistant Professor, Department of Aeronautics and Astronautics
Kyushu University, Japan
Zhenying Wang got her bachelor’s and master’s degree with honors in 2014 and 2017 from Tsinghua University, and PhD degree in 2019 from Kyushu University. She is interested in fluid-based energy systems, micro-nanoscale phase change, and wetting of complex liquids. She has been holding several research grants including two JSPS Kakenhi for Young Scientists, Toyota Scholar Program, KAO Crescent Award, and SHINKA grant with OIST. She is a recipient of several known awards including Droplets 2023 - Best Presentation Award for Young Scholars, 2021 Young Researcher Award of the Heat Transfer Society of Japan, 5th European Conference on Microfluidics - Best Presentation Award 1st place, and ASHRAE 2017 winter conference Best Paper Award. She is looking forward to discussing energy/cooling related issues, new visualization techniques and numerical methods with the attendees.
Abstract
Wetting and evaporation of droplets plays a significant role in liquid-based energy conversion, liquid cooling, and microfluidic devices. To date, our understanding of liquid-solid interaction has largely constraint to single component liquids, while this is not the case in real systems with the wide existence of salt, surfactants, contaminants, etc. The lack of knowledge leads to the out-control of those complex liquids, and greatly limits the technology development for liquid transport in practical scenarios.
In this talk, I will start from the basic mechanisims that govern the dynamic wetting of single component droplets, as can be scaled by the spatial-temporal interplay between capillary, evaporation, and thermal Marangoni effects. We elucidate and quantify these complex interactions using phase diagrams based on theoretical, numerical, and experimental investigations. A spreading law of evaporative droplets is derived by generalizing the classical Tanner’s law (valid for non-volatile liquids) to a wide range of liquids with saturation vapor pressure from 101 to 104 Pa and on substrates with thermal conductivity from 10−1 to 103 W/m/K. (Journal of Fluid Mechanics, 987, 2024, A15; Applied Physics Letters, 124.10, 2024, Editor’s Pick; Press Release at www.eurekalert.org/news-releases/1045204)
I will further extend the talk to more complex systems, such as, by adding a pinch of hygroscopic salt into the droplet. Due to the hygroscopic effect, the direction of vapor diffusion changes. The interfacial phase change (evaporation or vapor absorption) leads to spatiotemporal variation of the concentration field, introducing solutal Marangoni flow and resulting in more complex droplet behaviors demonstrated by contact line advancing, receding, and osilating. The approach demonstrates the significance of additional components in dynamic wetting, and provides another freedom for controllable droplet behaviors in practical conditions. (Journal of Fluid Mechanics, 912, 2021, A2; Physics Reports, 960, 2022, 1-37)
