Mesoscopic simulations of the diffusivity of ethane in beds of NaX zeolite crystals:: Comparison with pulsed field gradient NMR measurements
Mesoscopic simulations of the diffusivity of ethane in beds of NaX zeolite crystals:: Comparison with pulsed field gradient NMR measurements
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DOI：
10.1063/1.2567129
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发表时间：
2007-03-07
影响因子：
4.4
通讯作者：
Kaeger, Joerg
中科院分区：
文献类型：
--
作者：
Papadopoulos, George K.;Theodorou, Doros N.;Kaeger, Joerg
介观动力学Monte Carlo模拟和脉冲场梯度核磁共振（PFG NMR）测量进行了比较，以调查运输的乙烷在床上的NaX晶体。一种新的分子力学粒子为基础的重建方法，用于数字表示的床，使第一次并行研究的真实的系统和定制的计算机模型再现的空隙率，颗粒形状和平均尺寸的真实的系统。模拟的长程扩散的乙烷在床上的克努森，瞬态，和分子扩散制度是一致的PFG NMR测量产生曲折的因素，这取决于该政权的扩散，更具体地说，曲折的因素定义在传统的方式是较高的克努森比在分子扩散制度。详细的统计分析计算的分子轨迹表明，这种差异出现在一个非指数分布的长度和在碰撞之间的固体在克努森制度的路径段穿越的方向之间的相关性。当修正克努森曲折度以考虑这些特征时，在计算误差范围内获得了一个与制度无关的单一值。(c)2007年，美国物理学会。
Mesoscopic kinetic Monte Carlo simulations and pulsed field gradient nuclear magnetic resonance (PFG NMR) measurements are compared in order to investigate the transport of ethane in a bed of NaX crystals. A novel molecular mechanics particle-based reconstruction method is employed for the digital representation of the bed, enabling for the first time a parallel study of the real system and of a computer model tailored to reproduce the void fraction, particle shape and average size of the real system. Simulation of the long-range diffusion of ethane in the bed over the Knudsen, transient, and molecular diffusion regimes is consistent with the PFG NMR measurements in yielding tortuosity factors which depend upon the regime of diffusion; more specifically, tortuosity factors defined in the conventional way are higher in the Knudsen than in the molecular diffusion regime. Detailed statistical analysis of the computed molecular trajectories reveals that this difference arises in a nonexponential distribution of the lengths and in a correlation between the directions of path segments traversed between collisions with the solid in the Knudsen regime. When the Knudsen tortuosity is corrected to account for these features, a single, regime-independent value is obtained within the error of the calculations. (c) 2007 American Institute of Physics.