微通道内电解质溶液离子分布动电学效应模拟

THE SIMULATION OF INFLUENCE OF ELECTROKINETIC EFFECTS ON THE DISTRIBUTION CHARACTERISTIC OF ELECTROLYTE LIQUID IN MICROCHANNEL

动电学效应对微通道内流体流动特性影响很大,其对通道内粒子分布特性的影响使得通道近壁面流体流动特性极不稳定。本文采用分子动力学方法模拟了二维矩形微通道内NaCl稀电解质溶液的流动特性,考虑存在于不同粒子间的Lennard-Jones势能、静电力、以及带电离子与水分子间的相互作用,得到了粒子在通道内的分布特征。结果显示在动电学效应主要作用于通道壁面附近,而主流区域影响极小。Na^+离子在无量纲通道高度达到0.08和0.91时其浓度达到最大值,沿远离壁面其浓度逐渐降低,与壁面电性相反的Cl^-离子则在无量纲通道高度达到0.15和0.84附近浓度最高。其结果与基于连续介质解理论的Boltzamnn统计分布一致。水分子的浓度在壁面附近也较通道中心处高。

Electro-kinetic effects have a great impact on the flow characteristics of fluid in microchannels. The influences of electro-kinetic effects on the particles distribution could result in flow instability near the walls. In this paper, a molecular dynamics （MD） method is used to simulate the flow of the sodium chloride dilute solution in a two-dimension rectangular micro-channel. The Lennard-Jones （L-J） potential energy, Coulomb force and the ion-dipole interaction are taken into account to study the distribution property of the particles in the micro-flow. The simulation results show that electro-kinetic effects are in action significantly near the channel walls but ignorable in the bulk region. The peak concentrations of Na＋ ion occur at the position of about 0.91 and 0.08（non-dimensional width）, and the peak concentrations of Cl- occur at the position of about 0.84 and 0.15（non-dimensional width）.The simulation results are agreement with the Boltzmann statistics based on the continuum medium theory in a certain degree. The concentrations of water near the walls are higher than that in the bulk flow region.