甲烷水合物热导率分子动力学模拟及分析

采用平衡态分子动力学方法模拟分子甲烷水合物导热性能,结合声子态密度分析甲烷分子和水分子间的能量耦合过程;探究范德华相互作用对热导率温度相关性的影响。结果表明:热导率随着甲烷分子和水分子间范德华相互作用的增强而增大。相互作用的增强令甲烷分子的振动峰值向高频区域移动,使得甲烷分子与水分子间的振动耦合作用增强,VDOS匹配程度增加,进而增大了甲烷水合物的热导率。高温下的温度相关性归因于弛豫时间声子的出现导致的非弹性散射,低温下主要受到光学声子模式和低频声子的约束影响。模拟的热导率的温度依赖性与实验结果吻合较好。

Molecular dynamics simulation and analysis of thermal conductivity of methane hydrate

The heat conduction of methane hydrate was simulated using equilibrium molecular dynamics, and the thermal coupling between methane molecules and water lattices was studied by combining with the analysis of phonon density of states (VDOS). The influence of Van der Waals interaction strength on the temperature dependence of thermal conductivity was also investigated. The results show that the thermal conductivity increases proportionally with the enhancement of the Van der Waals interaction strength. With the increase of the interaction strength, the vibration peak of methane molecules shifts to a higher frequency region because of the stronger vibration coupling and the better matching of VDOS between methane molecules and water lattices, and then the thermal conductivity of methane hydrate is enhanced. The temperature dependence at high temperature may be attributed to inelastic scattering of the phonon caused by the appearance of phonons with the immediate relaxation time, while at low temperature it may be attributed to the confinement of the optic phonon modes and low frequency phonons. The calculated temperature dependence trend agrees well with the experimental results.