CAREER: A coupled multiscale study of phase change dynamics at curved liquid-vapor interfaces

University Of Cincinnati Main Campus, Cincinnati OH

Investigators

Abstract

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. The PI will also establish an “edible science” outreach program at the local farmers market focused on thermo-fluid science in the kitchen. The outreach effort leverages the research co-op program at the University of Cincinnati to promote undergraduate research while encouraging domestic minority student involvement. In addition, data communication workshops will be developed to train students on “storytelling with data” for the upcoming data driven job market. 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 (>10 μm), a microscale thin film submodel (<10 μm) and a nanoscale molecular dynamics submodel (<50 nm). 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. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.