Prabha Sooraj K, C P Abdul Gafoor, Sathian Sarith P
Department of Mechanical Engineering, Vidya Academy of Science and Technology, Thrissur 680501, India.
Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai 600036, India.
Phys Rev E. 2020 Aug;102(2-1):023303. doi: 10.1103/PhysRevE.102.023303.
Accommodation coefficients (ACs) are the phenomenological parameters used to evaluate gas-wall interactions. The gas transport through a finite length nanochannel will confront the variation of properties along the length of the channel. A three-dimensional molecular dynamics simulation has been carried out to examine this streamwise inhomogeneity of flow characteristics in a nanochannel. The rarefaction of the flow to the downstream direction is a crucial behavior in a pressure-driven nanochannel flow. This is manifested as the variation in velocity and temperature along the length of the channel. Subsequently, the interactions between the gas and wall particles will get reduced considerably. Moreover, the characteristics near the wall are examined in detail. A nonhomogeneous behavior in density and velocity profile near the wall is reported. Further, the momentum accommodation coefficient (MAC) in both the tangential and normal directions is examined along the lengthwise sections of the channel. The results show a significant variation of tangential and normal MACs along the length. Further, three channels with different length-to-characteristic dimension (L/H) ratios are considered to investigate the effect of L/H ratio. All three channels are subjected to the same pressure drop along the length. It is observed that the MACs and slip length show distinct behavior for different (L/H) ratios. The work establishes that the variation of MAC along the length of the channel has to be considered in modeling the nano- and microtransport systems.
适应系数（ACs）是用于评估气体与壁面相互作用的唯象学参数。气体通过有限长度的纳米通道传输时，会面临通道长度方向上性质的变化。已进行三维分子动力学模拟，以研究纳米通道中流动特性的这种流向不均匀性。在压力驱动的纳米通道流动中，流体向下游方向的稀薄化是一种关键行为。这表现为沿通道长度方向速度和温度的变化。随后，气体与壁面粒子之间的相互作用将大幅减少。此外，还详细研究了壁面附近的特性。报道了壁面附近密度和速度分布的非均匀行为。此外，沿着通道的纵向截面研究了切向和法向的动量适应系数（MAC）。结果表明，切向和法向MAC沿长度有显著变化。此外，考虑了三个具有不同长度与特征尺寸（L/H）比的通道，以研究L/H比的影响。所有三个通道沿长度方向承受相同的压降。观察到，对于不同的（L/H）比，MAC和滑移长度表现出不同的行为。这项工作表明，在对纳米和微传输系统进行建模时，必须考虑MAC沿通道长度的变化。
