Zhao Zhixiang, Zhou Runfeng, Sun Chengzhen
School of Urban Planning and Municipal Engineering, Xi'an Polytechnic University, Xi'an, Shaanxi 710048, China.
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China.
J Chem Phys. 2020 Dec 21;153(23):234701. doi: 10.1063/5.0030738.
The structure of nanoconfined fluids is particularly non-uniform owing to the wall interaction, resulting in the distinctive characteristic of thermal transport compared to bulk fluids. We present the molecular simulations on the thermal transport of water confined in nanochannels with a major investigation of its spatial distribution under the effects of wall interaction. The results show that the thermal conductivity of nanoconfined water is inhomogeneous and its layered distribution is very similar to the density profile. The layered thermal conductivity is the coupling result of inhomogeneous density and energy distributions that are generally diametrical, and their contributions to the thermal conductivity compensate with each other. However, the accumulative effect of water molecules is really dominating, resulting in a high thermal conductivity in the high-density layers with the low-energy molecules, and vice versa. Moreover, it is found that the adsorptive and repulsive interactions from solid walls have different roles in the hierarchical thermal transport in nanoconfined water. The adsorptive interaction is only responsible for the layered distribution of thermal conductivity, while the repulsive interaction is responsible for the overall thermal conductivity; accordingly, the thermal conductivity is independent of the strength of water-solid interactions. The identified hierarchical thermal transport in nanoconfined water and its underlying mechanisms have a great significance for the understanding of nanoscale thermal transport and even the mass and energy transport of nanoconfined fluids.
由于壁面相互作用，纳米受限流体的结构特别不均匀，这导致其与体相流体相比具有独特的热输运特性。我们对限制在纳米通道中的水的热输运进行了分子模拟，重点研究了壁面相互作用影响下其空间分布情况。结果表明，纳米受限水的热导率是不均匀的，其分层分布与密度分布非常相似。分层热导率是不均匀密度和能量分布的耦合结果，这两种分布通常是相反的，它们对热导率的贡献相互补偿。然而，水分子的累积效应确实起主导作用，导致低能量分子所在的高密度层具有较高的热导率，反之亦然。此外，发现固体壁面的吸附和排斥相互作用在纳米受限水的分层热输运中具有不同作用。吸附相互作用仅负责热导率的分层分布，而排斥相互作用则负责整体热导率；因此，热导率与水 - 固体相互作用的强度无关。所确定的纳米受限水的分层热输运及其潜在机制对于理解纳米尺度热输运乃至纳米受限流体的质量和能量输运具有重要意义。
