Department of Chemical Engineering, McMaster University, Hamilton, Ontario L8S 4L8, Canada.
J Chem Phys. 2012 Jul 28;137(4):044102. doi: 10.1063/1.4734484.
Nonequilibrium molecular dynamics (NEMD) simulations are used to investigate pressure-driven water flow passing through carbon nanotube (CNT) membranes at low pressures (5.0 MPa) typical of real nanofiltration (NF) systems. The CNT membrane is modeled as a simplified NF membrane with smooth surfaces, and uniform straight pores of typical NF pore sizes. A NEMD simulation system is constructed to study the effects of the membrane structure (pores size and membrane thickness) on the pure water transport properties. All simulations are run under operating conditions (temperature and pressure difference) similar to a real NF processes. Simulation results are analyzed to obtain water flux, density, and velocity distributions along both the flow and radial directions. Results show that water flow through a CNT membrane under a pressure difference has the unique transport properties of very fast flow and a non-parabolic radial distribution of velocities which cannot be represented by the Hagen-Poiseuille or Navier-Stokes equations. Density distributions along radial and flow directions show that water molecules in the CNT form layers with an oscillatory density profile, and have a lower average density than in the bulk flow. The NEMD simulations provide direct access to dynamic aspects of water flow through a CNT membrane and give a view of the pressure-driven transport phenomena on a molecular scale.
非平衡分子动力学（NEMD）模拟用于研究在低压（5.0 MPa）下通过碳纳米管（CNT）膜的水流，这种低压是实际纳滤（NF）系统的典型压力。CNT 膜被建模为具有光滑表面和典型 NF 孔径的均匀直孔的简化 NF 膜。构建了一个 NEMD 模拟系统来研究膜结构（孔径和膜厚）对纯水输运性质的影响。所有模拟都是在与实际 NF 过程相似的操作条件（温度和压差）下运行的。分析模拟结果以获得沿流动和径向方向的水通量、密度和速度分布。结果表明，在压差下通过 CNT 膜的水流具有非常快速流动的独特输运性质，以及不能用哈根-泊谡叶或纳维-斯托克斯方程表示的非抛物线径向速度分布。沿径向和流动方向的密度分布表明，CNT 中的水分子形成具有振荡密度分布的层，并且平均密度低于体相流动中的密度。NEMD 模拟提供了对 CNT 膜中水流动的动态方面的直接访问，并提供了在分子尺度上对压力驱动输运现象的了解。
