Ghorbanian Jafar, Beskok Ali
Department of Mechanical Engineering, Southern Methodist University, Dallas, TX 75205, USA.
Phys Chem Chem Phys. 2017 Apr 19;19(16):10317-10325. doi: 10.1039/c7cp01061c.
This paper concentrates on the unconventional temperature profiles and heat fluxes observed in non-equilibrium molecular dynamics (MD) simulations of force-driven liquid flows in nano-channels. Using MD simulations of liquid argon flows in gold nano-channels, we investigate the manifestation of the first law of thermodynamics for the MD system, and compare it with that of the continuum fluid mechanics. While the energy equation for the continuum system results in heat conduction determined by viscous heating, the first law of thermodynamics in the MD system includes an additional slip-heating term. Interaction strength between argon and gold molecules is varied in order to investigate the effects of slip-velocity on the slip-heating term and the resulting temperature profiles. Heat fluxes and temperature profiles from "continuum", "continuum augmented with slip-heating", and "heat conduction due to the power input by the driving force" are modeled and compared with the MD results. The continuum model can neither predict the heat fluxes nor the temperature profiles from MD simulations. While the continuum model augmented with slip-heating matches the MD heat fluxes, the resulting temperature profiles do not agree with the MD predictions. Overall the analytical model based on "heat conduction due to power input by the driving force" matches the heat fluxes from MD simulations, while the temperature profiles match MD predictions using an effective thermal conductivity that is about 70% of the thermodynamic value. Using different liquid-wall pairs affects the slip velocity, temperature jump, and the resulting thermal conductivity of the fluid, but results in similar physical observations. The inability of the MD method in mimicking continuum fluid mechanics in energy transport for force-driven liquid flows is scale independent, and it is more likely a numerical artifact.
本文聚焦于在纳米通道中力驱动液体流动的非平衡分子动力学（MD）模拟中观察到的非常规温度分布和热通量。通过对金纳米通道中液态氩流动的MD模拟，我们研究了MD系统中热力学第一定律的表现形式，并将其与连续介质流体力学的表现形式进行比较。对于连续介质系统，能量方程导致由粘性加热决定的热传导，而MD系统中的热力学第一定律包含一个额外的滑移加热项。改变氩分子与金分子之间的相互作用强度，以研究滑移速度对滑移加热项及由此产生的温度分布的影响。对“连续介质”、“增加滑移加热的连续介质”以及“由驱动力输入功率引起的热传导”的热通量和温度分布进行建模，并与MD结果进行比较。连续介质模型既无法预测MD模拟中的热通量，也无法预测温度分布。虽然增加滑移加热的连续介质模型与MD热通量相匹配，但由此产生的温度分布与MD预测结果不一致。总体而言，基于“由驱动力输入功率引起的热传导”的解析模型与MD模拟中的热通量相匹配，而温度分布则与使用约为热力学值70%的有效热导率的MD预测结果相匹配。使用不同的液 - 壁对会影响滑移速度、温度跳跃以及由此产生的流体热导率，但会得出相似的物理观测结果。MD方法在模拟力驱动液体流动能量传输中的连续介质流体力学方面的无能与尺度无关，而且更可能是一种数值假象。
