汽液界面动力学行为与热力学性质的分子动力学研究

本文采用分子动力学方法研究了热平衡条件下的汽液界面的动力学行为和热力学性质。统计获得了界面区的密度、压力张量及温度的分布，并且从分子层次观察分析了界面结构和动力学特性。研究表明汽液界面是一个随时间起伏涨落的曲面，界面层的分子并不是处于液相和蒸汽相之间的一种过渡状态，从汽相到液相密度的连续变化是长时间的统计结果，汽渡过渡区的厚度与汽液界面区的密度涨落的范围是一致的。对于平衡条件下的汽液界面，由于汽液相变的影响，在紧贴界面处存在一个分子平均动能非平衡分布的区域。此非平衡区域的存在与汽液两相的宏观热平衡并不矛盾，但可能对蒸发／凝结流率的估计有不可忽略的影响。

MOLECULAR DYNAMICS STUDY ON THE DYNAMIC BEHABIORS AND THERMO- DYNAMIC PROPERTIES OF THE LIQUID-VAPOR INTERFACE

Dynamic behaviors and thermodynamic properties of liquid-vapor interface at equilibrium are studied with molecular dynamics simulations. The density, the pressure tensor, and the temperature profiles are obtained. Meanwhile, the structure and the dynamic behavior of the interface are analyzed from the molecular level. The simulations show that, for the liquid-vapor coexistent system, there is a local thermal non-equilibrium area close to the liquid surface because of the liquid-vapor phase change, while thermal equilibrium condition is attained outside the interface more than several molecules' diameters. In addition, simulation and experiment show that the liquid-vapor interface is a wavy surface undulating with time, and the change of the local density from the liquid to the vapor is abrupt, the continuous density profiles are only statistical results. The thermal non-equilibrium distribution through the interface region is caused by the energy transport between the liquid and the vapor phase. For the reason of the small size of the non-uniform temperature area, the existence of the local non-equilibrium area does not conflict with the macroscopic thermal equilibrium theory. However, the thermal non-equilibrium distribution may work on the liquid-vapor phase change and have effect on the estimation of evaporation/ condensation flux.