Nonequilibrium molecular dynamics (NEMD) modeling of nanoscale hydrodynamics of clay‐water system at elevated temperature
Nonequilibrium molecular dynamics (NEMD) modeling of nanoscale hydrodynamics of clay‐water system at elevated temperature
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DOI：
10.1002/nag.3325
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发表时间：
2021-12
影响因子：
4
通讯作者：
Zhe Zhang;Xiaoyu Song
中科院分区：
文献类型：
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作者：
Zhe Zhang;Xiaoyu Song
涉及非等温条件下的粘土的工程问题(如地热能收集、垃圾覆盖系统和核废料处理)本质上是多尺度和多物理的。粘土在高温下的纳米尺度流体动力学是建立非等温条件下基于物理的多尺度粘土模型的基础。非平衡分子动力学(NEMD)是研究粘土纳米尺度流体动力学的有效工具。本文提出了一种粘土纳米孔高温流体动力学的NEMD模型。研究了叶蜡石和蒙脱石纳米孔中的水流动。通过在每个水分子上均匀地施加外力来维持非平衡状态。NEMD模拟提供了温度对粘土-水密度、水流速度、剪切粘度、粘土-水滑移长度、渗透系数和粘土-水摩擦系数影响的分子尺度视角。数值结果表明，流体流动速度、剪切粘度、粘土-水滑移长度和渗透系数在纳米尺度上与温度有很强的相关性。我们验证了立方定律在确定高温下纳米孔尺度的水力传导性方面的适用性。从数值结果可以看出，滑移粘土-水边界条件是合理确定纳米流体流动速度的重要因素。通过数值算例，研究了纳米孔尺寸和粘土层厚度对粘土-水体系流体动力学的影响。
The engineering problems involving clay under non‐isothermal conditions (e.g., geothermal energy harvest, landfill cover system, and nuclear waste disposal) are multiscale and multiphysics by nature. The nanoscale hydrodynamics of clay at elevated temperature is essential in developing a physics‐based multiscale model for clay under non‐isothermal conditions. The nonequilibrium molecular dynamics (NEMD) is a useful tool to study the nanoscale hydrodyndamics of clay. This article presents an NEMD modeling of hydrodynamics of clay nanopores at elevated temperatures. Water flow confined in pyrophyllite and montmorillonite clay nanopores is investigated. The nonequilibrium state is maintained by uniformly exerting an external force on each water molecule. The NEMD simulations have provided a molecular‐scale perspective of temperature effect on clay‐water density, water flow velocity, shear viscosity, clay‐water slip length, hydraulic conductivity, and clay‐water friction coefficient. The numerical results have shown a strong temperature dependence of fluid flow velocity, shear viscosity, clay‐water slip length, and hydraulic conductivity at the nanoscale. We have validated the applicability of cubic law in determining hydraulic conductivity at the nanopore scale at elevated temperatures. It is found from our numerical results that slip clay‐water boundary condition is an essential factor in properly determining nanoscale fluid flow velocity. By numerical examples, we also study the impact of nanopore size and clay layer thickness on the hydrodynamics of the clay‐water system.