Molecular Dynamics Study on Influence of Wetting Contact State of Microchannel Nanostructures on Sliding Drag Reduction
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摘要: 针对流体在纳米通道的微尺度流效应，采用分子动力学方法以SPC/E水分子为纳米流动介质，分别计算模拟其在不同纳米结构的微通道内的润湿接触状态和Poiseuille流动行为，研究通过微通道壁面微纳结构改变而导致的不同润湿状态起到的滑移减阻效应。结果表明：纳米结构的周期性增加，会使得壁面的亲疏水性呈现马太效应，从而达到润湿性控制的目的。增加壁面亲水性，会使主流区密度、流体速度和滑移速度都减小；在增加壁面疏水性的过程中，主流区的密度增加；并且流体的状态由Wenzel向Cassie转变，流体速度和滑移长度先减小后增加；而亲疏水转变过程中，随着表征接触角的增加，当动静态流体与壁面的接触状态相同时，流体流动的壁面摩擦因数值呈现单调递减趋势；而当动静态流体与壁面的接触状态存在差异时，摩擦因数会出现轻度无规律波动。Abstract: Aiming at the nanofluidics effect of fluid in nano-channels, the wetting contact state and Poiseuille flow behavior of SPC/E water molecules are calculated and simulated respectively with the molecular dynamics methodin micro-channels with different nano-structures to study the sliding drag reduction effect of different wetting states caused by the micro-nano structure change of the microchannel wall surface. The results show that the periodicity of nano-structures increases, which makes the wettability of the wall surface show Matthew effect, thus achieving the purpose of wettability control. Increasing the hydrophilicity of the wall will reduce the density of the main flow region, fluid velocity and slip velocity. In the process of increasing the hydrophobicity of the wall surface, the density of the main flow region increases. The state of the fluid changes from Wenzel to Cassie, and the fluid velocity and slip length decrease first and then increase. In the process of wettability transition, with the increase of the characteristic contact angle, the wall friction coefficient of fluid flow shows a monotonic decreasing trend when the contact states of dynamic and static fluids on the wall are the same. However, when the contact state of static and dynamic fluids on the wall is different, the friction coefficient will fluctuate slightly and irregularly.
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Key words:
- microchannel /
- wettability /
- velocity slip /
- slip length /
- friction coefficient
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表 1 各原子之间的LJ势能参数
参数 数值 εO-O /(kcal·mol−1) 0.155 35 εCu-O(q)/(kcal·mol−1) 0.788 41 εCu-O(s)/(kcal·mol−1) 0.192 37 σO-O /Å 3.166 σCu-Cu/Å 2.34 σCu-O/Å 2.753 
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表 2 不同织构周期的壁面参数和表征接触角
T θ0 = 78.9° θ0 = 102° r θW/(°) r或f θW/(°) 2 1.112 77.6 r = 1.112 103.4 4 1.224 76.4 r = 1.224 104.7 6 1.337 75.1 f = 0.122 151.3 8 1.449 73.8 f = 0.113 155.5 10 1.561 72.5 f = 0.08 159.5
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