RUI: Thermal Transport across Liquid-gas Interfaces

微/纳米液滴的蒸发和冷凝对于诸如喷雾冷却、喷雾燃烧和云形成的各种工程和环境应用是非常重要的。准确预测这些小液滴的蒸发/冷凝速率对于在这些应用中实现微米/纳米液滴的更有效使用至关重要。虽然蒸发和冷凝过程已经研究了世纪，现有的蒸发和冷凝过程模型的关系往往预测的结果是不一致的，甚至与实验数据相矛盾。该项目的主要目标是使用数值和理论方法从根本上了解跨液-气界面的传热和传质，并评估液-气界面的热阻，以帮助阐明这些不一致性。教育活动将吸引中央谷（加州）代表性不足的高中生加入工程项目，培养学生进行微/纳米级传热研究，并指导少数民族学生攻读博士学位。两种传热机制，即蒸发和热传导，经常同时发生在蒸发液体表面，例如空气中的水蒸发。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）模拟与气体动力学理论相结合，定量分析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模拟可以以高保真度确定液-气界面附近的流体的温度、密度和质量适应系数，这允许验证模拟液-气界面处的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，该项目将为蒸发/冷凝过程的连续级建模导出合适的边界条件。该奖项反映了NSF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.