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Molecular Study of Phase Change Phenomena of Methanol and Water Vapors in Wide Ranges of Vapor-Liquid Non-equilibrium State

宽范围汽液非平衡状态下甲醇和水蒸气相变现象的分子研究

基本信息

批准号：
14350087
负责人：
FUJIKAWA Shigeo
金额：
$ 6.34万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

The boundary condition for the Boltzmann equation at a vapor-liquid interface is found to be, on the basis of molecular dynamics, the product of three one-dimensional Maxwellians for the three velocity components of vapor molecules and a factor including well-defined condensation coefficient. The Maxwellian for the velocity component normal to the interface is characterized by the liquid temperature, while those for the tangential components are prescribed by a different temperature which is a linear function of energy flux across the interface. The condensation coefficient is found to be constant and equal to the evaporation coefficient determined by the liquid temperature alone.Numerical simulations of molecular gas dynamics are presented for the determination of condensation coefficient of methanol vapor from experimental data with a shock tube. The boundary condition for the Boltzmann equation is rewritten using the net condensation mass flux estimated by the shock tube experiment, and the evaporation and condensation coefficients are eliminated in the boundary condition. Thereby, the numerical solution of the vapor-liquid system is uniquely obtained for a given net condensation mass flux, and the instantaneous relation between the evaporation and condensation coefficients and vapor-liquid system can be examined from the mass conservation equation through the interface. The result shows that the condensation coefficient takes values from 0.7 to 0.9, which are dose to that of the evaporation coefficient evaluated in the molecular dynamics simulation.

本文从分子动力学的角度出发，将玻尔兹曼方程在汽液界面上的边界条件看作是汽相分子三个速度分量的三个一维麦克斯韦方程与一个包含凝结系数的因子的乘积。垂直于界面的速度分量的麦克斯韦方程的特征在于液体温度，而切向分量的麦克斯韦方程的特征在于不同的温度，该温度是穿过界面的能通量的线性函数。发现冷凝系数是常数，等于由液体温度单独决定的蒸发系数.用分子气体动力学方法对激波管测量甲醇蒸汽冷凝系数的实验数据进行了数值模拟.用激波管实验估算的净凝结质量通量改写了Boltzmann方程的边界条件，并在边界条件中去掉了蒸发和凝结系数。由此，对于给定的净冷凝质量通量，可唯一地得到汽液系统的数值解，并可由通过界面的质量守恒方程考察蒸发系数和冷凝系数与汽液系统的瞬时关系。结果表明，冷凝系数取值范围为0.7 ~ 0.9，与分子动力学模拟计算的蒸发系数取值范围相近。