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MOLECULAR DYNAMICS STUDY ON CONDENSATION/EVAPORATION PROCESSES AND CONDENSATION COEFFICIENT

缩合/蒸发过程及缩合系数的分子动力学研究

基本信息

批准号：
06650259
负责人：
TSURUTA Takaharu
金额：
$ 1.54万
依托单位：
KYUSHU INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

The study was conducted for a molecular-scale clarification of the condensation process at an interface between liquid and vapor phases. The molecular dynamics method was used to simulate the behavior of a monatomic molecule colliding with the liquid surface and the effects of translational motion on condensation probability were investigated. The simulations have been performed for the argon-molecule system consisting of 864 molecules. The following findings have been derived :(1)In the case that the incident molecule is captured by the liquid phase, the molecule repeats the collisions several times within the interface zone and loses its kinetic energy. Through some collisions the kinetic and potential energies approach to the mean values of the liquid-film system, then the process of phase transformation from the vapor to the liquid is completed. Most of incident molecules condense in this manner. In the case of reflecting molecules, on the other hand, the number of collisions is small. The molecules posses enough energy to escape from the liquid surface even after the collision. Some molecules get the energy at the collision with the surface molecules.(2)The condensation probability depends on the normal component of the kinetic energy of the incident molecule. At the temperature of 84 K,the probability increases from 0.9 to 0.97 with the increase of the normal component of the incident energy. Since the molecules with small normal component of incident energy gain the energy at the collisions with the surface molecules, the condensation probability is smaller than those with large one. The molecules having the large translational energy can penetrate the interface zone and can condense by repeating the collisions with the liquid molecules. The molecular scale irregularity of the surface may cause the iterative collisions, which raise the probability of condensation.

该研究的目的是对液相和气相界面的冷凝过程进行分子尺度的澄清。采用分子动力学方法模拟单原子分子与液体表面碰撞的行为，研究平动运动对凝聚概率的影响。模拟是针对由 864 个分子组成的氩分子系统进行的。得出以下结论：(1)在入射分子被液相捕获的情况下，分子在界面区域内重复碰撞多次并失去动能。通过一些碰撞，动能和势能接近液膜系统的平均值，从而完成从蒸气到液体的相变过程。大多数事件分子以这种方式凝结。另一方面，在反射分子的情况下，碰撞次数很少。即使在碰撞后，分子也具有足够的能量从液体表面逸出。有些分子在与表面分子碰撞时获得能量。(2)凝聚概率取决于入射分子动能的法向分量。在84 K温度下,随着入射能量法向分量的增加,概率从0.9增加到0.97。由于入射能量法向分量较小的分子在与表面分子碰撞时获得能量，因此凝聚概率比入射能量法向分量较大的分子小。具有大平动能的分子可以穿透界面区，并且可以通过与液体分子重复碰撞而凝结。表面分子尺度的不规则性可能会导致迭代碰撞，从而增加凝结的可能性。