Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 172731

A Coupled Multiscale Study of Phase Change Dynamics at Curved Liquid-Vapor Interfaces 

Liquid-vapor surfaces are ubiquitous in natural and engineered devices. A cup of coffee, a tree, and an air-conditioning unit, all have liquid-vapor interfaces and are undergoing "evaporation" in some form. Curved interfaces with contact lines (such as droplets, menisci, and thin films) exhibit unique properties due to surface tension that significantly alters evaporation/condensation. In turn, the evaporation/condensation moves the liquid-vapor interface. The intricate coupling between evaporation/condensation and interface dynamics becomes important when surface tension is the dominant force. However, this coupling is still not well understood. In the project, the dynamic stability of liquid-vapor interfaces is investigated using experiments coupled with modeling. The proposed work will advance fundamental understanding of phase change at curved liquid-vapor surfaces and enable the development of advanced technologies that involve thin films and contact lines. The application areas include manufacturing, boiling, porous media transport, electronics cooling, micro-scale heat transfer devices, decarbonization, hydrogen technology, and food-water-energy nexus.

Evaporating thin films are critical to the development of devices in a wide variety of industries. However, a complete understanding is still lacking, in part, due to the complex coupling between phase change and capillarity/wetting dynamics. A curved interface exhibits non-uniform phase change flux due to the existence of an adsorbed film. This film is in a metastable condition balanced by thermal and mechanical contributions to phase change. It is anticipated that a spatiotemporal mismatch of the thermal and mechanical effects at the nanoscale results in dynamic film oscillations, influences contact line motion, macroscale stability, and overall phase change heat transfer, and is a major contributor to the ?stick-slip? phenomena. However, direct measurements of both the thermal and mechanical factors have not been made thus far due to the very small length scales involved. In this project, the dynamic phase change driven stability of the curved liquid-vapor interfaces is investigated through a unique combination of experiments and modeling. The novel experiment will simultaneously measure film thickness/curvature and wall temperature with high spatiotemporal resolution in a single dual-interferometry setup. This is complemented by a transient multiscale computational model consisting of a macroscale computational fluid dynamics submodel (>10μm), a microscale thin film submodel (<10μm) and a nanoscale molecular dynamics submodel (<50nm). Using a coupled approach, the influence of phase change driven (in)stability at the micro/nanoscale on macroscale contact line motion will be investigated. The project will enable a fundamental understanding of the appropriate boundary conditions and enable new insights into the complex coupling between multiple length scales.

Presenting Author: Kishan Bellur University of Cincinnati

Presenting Author Biography: Dr. Bellur is an Assistant Professor in Department of Mechanical & Materials Engineering at University of Cincinnati. He received his BS in Mechanical Engineering from Milwaukee School of Engineering in 2013. He then briefly worked as a hydraulics engineer at The Raymond Corp. in Greene, NY before starting graduate school at Michigan Tech. He received an MS in 2016 and PhD in 2018, both in Mechanical Engineering. He received postdoctoral training at Michigan Tech and University of Michigan. His research is focused on liquid-vapor phase change (evaporation/condensation) and associated interfacial phenomena. He leads the UC Lab for Interfacial Dynamics (UCLID).

Authors:

Kishan Bellur University of Cincinnati