纳米尺度通道中气体粘度的分子动力学模拟

Molecular dynamics simulation of gas viscosity in nano-scale channels

利用非平衡分子动力学方法模拟了气体在纳米尺度通道中的运动特性,统计获得通道中流动的速度剖面和剪切应力分布,并利用牛顿粘性定律首次获得了纳米尺度通道中的等效粘度分布。结果表明,纳米尺度通道中的粘度不是一个常数。在壁面附近,由于壁面原子和气体分子的相互作用,存在壁面效应,气体的粘度较小;而通道中心区域的粘度与实验结果符合较好,壁面对粘度的影响范围为20 nm左右。通道高度对中心区域粘度的影响很小,而温度对其的影响较大,粘度值随温度的增加而增大。不同通道高度下,壁面附近粘度的分布几乎一致;不同温度时,壁面附近粘度的分布随温度的增加而增加。

Gas flows in nano-scale channels were studied by using the nonequilibrium molecular dynamics simulation.The velocity profile and shear stress distribution across the channel were first obtained.The distribution of effective viscosity across the channel was then obtained for the first time by using the Newton viscosity law.The simulation indicates that the viscosity in the nano-scale channel was not identical.The local gas viscosity decreases when approaching the wall,because of the interactions between wall and gas molecules.However,the effective viscosity in the bulk region of the channel agrees very well with the experiment data.The wall influencing depth is about 20 nm.The bulk viscosity of gas in nano-scale channel doesn＇ t vary with channel height.However,it increases with the increase of gas temperature.The distributions of viscosities near the wall are identical at different channel heights,but increased with the increase of temperature.