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

液体-蒸汽表面在自然和工程装置中无处不在。一杯咖啡、一棵树和一台空调，都有液-气界面，都在以某种形式“蒸发”。具有接触线的弯曲界面（如液滴、半月板和薄膜）由于表面张力而表现出独特的特性，这显著地改变了蒸发/冷凝。反过来，蒸发/冷凝移动了液-气界面。当表面张力是主导力时，蒸发/冷凝和界面动力学之间的复杂耦合变得重要。然而，这种耦合仍然没有得到很好的理解。本课题采用实验与模型相结合的方法研究了液-气界面的动态稳定性。所提出的工作将促进对弯曲液汽表面相变的基本理解，并使涉及薄膜和接触线的先进技术的发展成为可能。应用领域包括制造、煮沸、多孔介质输送、电子冷却、微尺度传热装置、脱碳、氢技术和食物-水-能源关系。PI还将在当地农贸市场建立一个“食用科学”外展项目，重点关注厨房中的热流体科学。推广工作利用了辛辛那提大学的研究合作项目，以促进本科生的研究，同时鼓励国内少数民族学生的参与。此外，还将举办数据交流讲习班，培训学生“用数据讲故事”，以应对即将到来的数据驱动型就业市场。蒸发薄膜对各种工业设备的发展至关重要。然而，由于相变和毛细/润湿动力学之间的复杂耦合，仍然缺乏完整的理解。由于吸附膜的存在，弯曲界面表现出不均匀的相变通量。该薄膜处于亚稳态状态，由热和机械对相变的贡献来平衡。预计在纳米尺度上，热效应和力学效应的时空不匹配会导致薄膜的动态振荡，影响接触线运动、宏观尺度稳定性和整体相变传热，并且是“粘滑”现象的主要原因。然而，由于涉及的长度尺度非常小，迄今为止还没有对热和机械因素进行直接测量。在本项目中，通过独特的实验和建模相结合的方法，研究了弯曲液-气界面的动态相变驱动稳定性。该实验将在单一双干涉测量装置中以高时空分辨率同时测量薄膜厚度/曲率和壁温。该模型由宏观计算流体动力学子模型（10 μm）、微尺度薄膜子模型（10 μm）和纳米尺度分子动力学子模型（50 nm）组成。采用耦合方法，将研究微/纳米尺度相变驱动的稳定性对宏观接触线运动的影响。该项目将使人们对适当的边界条件有一个基本的了解，并使人们对多个长度尺度之间的复杂耦合有新的认识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.