纳米通道内液态微流动密度分布特性数值模拟研究

Simulation studies on fluid density distribution of micro-flows in a nano-channel

微通道内流动因表面积/体积比值极大,造成许多微尺度效应,进而使微通道内出现完全不同于宏观流动的流体密度分布特性.本文以纳米通道内液态Poiseuille流为对象,采用非平衡分子动力学模拟方法研究了流体原子间相互作用强度εLL,流体原子间平衡距离σLL以及壁面原子与流体原子间平衡距离σLS对通道内流体密度分布的影响规律.数值模拟中,统计系综取微正则系综,势能函数选用LJ/126模型,壁面设为Rigid-atom壁面,温度校正使用速度定标法,牛顿运动方程的求解则采用Verlet算法.模拟结果表明,随εLL的减弱,近壁面区密度分布的振荡幅度则逐渐增大;而σLL则同时影响流体原子的存在形态和密度分布,较大的σLL会造成流体原子在整个通道内呈现面心立方结构的类似固体排列,较小的σLL会使得流体原子呈现不断变化的"团簇"结构;随σLS的变大,近壁面区流体密度振荡幅度增大,且流体密度分布起点离壁面越远.另外,本文还从近壁面区流体原子的"俘获-逃逸"行为角度,初步解释了原子间相互作用强度对密度分布的影响规律.

The flow in microchannel involves many microscale effects, because of its large ratio of superficial area to volume. And it further causes the density profiles of flow in microchannel to be greatly different from in the macro-channel. In this paper we investigate the effects of three factors （eLL, trLL, CrLS） on density profile of micro-flow via the Poiseuille flow in a nanochannel using none-equilibrium molecular dynamics simulation method. In our study, we selected NVE as the statical ensemble, LJ/126 model as the potential energy function. We also adopt the Rigid-atom model to describe the wall and the temperature thermostat through using the time/rescale methods. The motion equations are solved using Verlet algorithm. The results show that as the interaction between flow atoms decreases, the oscillation degree of density profiles near the wall increases. The balance distance （aLL） between flow atoms affects the existence state and density profiles of flow in the micro channel： the greater CrLL causes the flow atoms to be arranged as the fcc structure liking a solid, while smaller CrLL results in the flow atoms moving as a changeable ＂cluster＂. The balance distance （tYLS） between wall atoms and flow atoms also has a significant influence on flow density. As trLS increases, the oscillation degrees of density profile near the wall and the distance between the starting point of density profile and wall increase. Besides, we analyze the mechanism of effects of the interaction between the flow atoms on density distribution based on the ＂capture-escape＂ behavior of atoms adjoining the wall.