Session: Government Agency Student Posters

Paper Number: 173505

Multiscale Oscillations in Thin Liquid Films 

Wetting liquids form menisci with an extended thin liquid film near the three-phase contact line. Due to increased heat transfer from the solid wall, this region experiences high evaporation rates. Thin film evaporation is critical to several engineering applications such as heat pipes, MEMS, and cryogenic fuel storage. As the thickness of the liquid film decreases, the complex interplay between molecular interactions, surface forces, and phase change dynamics gives rise to multiscale oscillations in the liquid film. Experimental studies have observed film oscillations ranging from nanometers to millimeters; however, the multiscale nature of this phenomenon poses a challenge for computational models. Oscillations in the extended meniscus region are also influenced by contact line motion. In this study, we present a two-part approach to modeling the multiscale oscillations in thin liquid films by bridging molecular dynamics simulations with continuum models. Simulations of evaporation in nanoscale channels and confined bubbles are performed using molecular dynamics methods. Statistical analysis of the molecular data is performed to obtain thermodynamic properties. An energy-based interface detection technique is used to identify the liquid-vapor interface and track oscillations. Values of the evaporation and condensation accommodation coefficients are calculated from the molecular dynamics data using the mass and energy conservation laws and kinetic theory. The commonly assumed equivalence of the accommodation coefficients is tested. It is shown that small variations in the values of the accommodation coefficients lead to large errors in the heat and mass transfer predictions. While molecular dynamics studies provide valuable data, they are limited to the nanoscale. Tracking film oscillations across the length and time scales requires continuum-scale computational models. Classical thin film models are based on the Young-Laplace pressure balance and rely on the one-dimensional lubrication approximation; however, two-dimensional flows are observed in the molecular dynamics simulations due to highly non-uniform phase change rates along the liquid-vapor interface and phase change-induced Marangoni stresses. A novel continuum model is developed combining the thin film equation, the vorticity-streamfunction equations, the heat equation, and the kinetic theory-based phase change equations. Evaporation rates computed using kinetic theory are used as inputs to the vorticity-streamfunction equations and the heat equation as a boundary condition. Values of the accommodation coefficients from the molecular dynamics study are used as inputs to the continuum model. Phase change mass flux, interface shape, and flow patterns are compared between the continuum and molecular dynamics simulations, providing a method to study liquid film oscillations across length scales.

Presenting Author: Ayaaz Yasin University of Cincinnati

Presenting Author Biography: Ayaaz Yasin is a PhD student in the Department of Mechanical Engineering at the University of Cincinnati, working with the UC Lab for Interfacial Dynamics under the supervision of Dr. Kishan Bellur. His research primarily focuses on understanding and modeling liquid-vapor phase change and related interfacial phenomena.

Authors:

Ayaaz Yasin University of Cincinnati
Unmeelan Chakrabarti University of Cincinnati
Kishan Bellur University of Cincinnati