RUI: Thermal Transport across Liquid-gas Interfaces

微/纳米液滴的蒸发和冷凝在喷雾冷却、喷雾燃烧和云的形成等各种工程和环境应用中具有重要意义。为了在这些应用中更有效地利用微/纳米液滴，准确预测这些小液滴的蒸发/冷凝速率至关重要。尽管蒸发和冷凝过程的研究已经进行了一个多世纪，但现有的蒸发和冷凝过程模型的预测结果往往与实验数据不一致，甚至与实验数据相矛盾。本项目的主要目的是利用数值和理论方法从根本上了解液气界面的传热传质，并评估液气界面的热阻，以帮助阐明这些不一致性。这些教育活动将吸引加州中央山谷地区代表性不足的高中生参加工程项目，培训学生进行微/纳米尺度传热研究，并指导少数民族学生攻读STEM博士学位。蒸发和热传导两种传热机制往往同时发生在蒸发液体表面，如空气中的水蒸发。为了阐明这两种机制在液气界面传热中的作用，本项目使用分子动力学（MD）模拟结合气体动力学理论，定量分析了各种驱动力条件下蒸发/冷凝液体表面的传热和传质。此外，MD模拟可以高保真地确定液气界面附近流体的温度、密度和质量容纳系数，从而可以验证在液气界面模拟传热和传质的各种关系。基于MD模拟结果和动力学理论分析，本项目将推导出适合连续水平蒸发/冷凝过程建模的边界条件。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。

Evaporation and condensation of micro/nanodroplets are of great importance to various engineering and environmental applications such as spray cooling, spray combustion, and cloud formation. It is essential to accurately predict the evaporation/condensation rates for these small droplets for achieving a more efficient use of micro/nanodroplets in these applications. Although evaporation and condensation processes have been studied for over a century, the existing relationships that model evaporation and condensation processes often predict results that are inconsistent with, or even contradictive to experimental data. The main objective of this project is to use numerical and theoretical methods to fundamentally understand heat and mass transfer across liquid-gas interfaces, and evaluate the thermal resistance at liquid-gas interfaces to help elucidate these inconsistencies. The education activities will attract underrepresented high school students in the central valley (California) to the engineering program, train the students to conduct research in micro/nanoscale heat transfer, and guide minority students to Ph. D. programs in STEM.Two heat transfer mechanisms, namely, evaporation and heat conduction, often occur simultaneously at evaporating liquid surfaces, such as the water evaporation in air. To elucidate the roles of each of the two mechanisms in heat transfer across liquid-gas interfaces, this project uses molecular dynamics (MD) simulations coupled with the kinetic theory of gases to quantitatively analyze heat and mass transfer at evaporating/condensing liquid surfaces under a variety of driving force conditions. Furthermore, MD simulations can determine the temperature, density, and the mass accommodation coefficient of fluid near the liquid-gas interface with high fidelity, which allows the validation of the various relationships that model the heat and mass transfer at liquid-gas interfaces. Based on MD simulation results and kinetic theory analysis, this project will derive appropriate boundary conditions for continuum-level modeling of evaporation/condensation processes.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.