摘要:
使用分子动力学方法,研究过热水系统均质沸腾核化过程.采用Langerin动力学方法控制体积可变系统的温度与压力,更好地模拟了沸腾实际物理过程.得到了液相系统体积连续膨胀、分子间距逐渐增大,最终稳定在汽相的现象学规律,当过热温度较高时,亚稳态液相系统可能在局部形成不同大小的近球形区域:气核,这些气核是不稳定的,处于不断演化之中,通过分析分子所受引力与斥力的共同作用,得到了气核形成与消亡以及多个气核融合的机理,比较了模拟结果与经典沸腾理论的差异,提出了气核生长是比气泡生长更为微观过程的认识.通过研究不同过热度系统,得到了模拟条件下水的均质沸腾临界过热温度为535 K左右,在已有的实验结果范围内.
Abstract:
This study uses molecular dynamics simulation to analyze the homogeneous nucleation process in superheated water. The temperature and pressure of the system are controlled with Langevin dynamics method while the system volume is variable. In this way, the expanding process of the liquid system into vapor system is studied phenomenologically. In metastable liquid system with higher superheating degree, there can be seen large quantities of regions with no liquid moleculer inside: i.e., the vapor embryos. These vapor embryos are unstable in nature and are deforming with time. By analyzing the attraction and repulsion between molecules, we find the mechanisms that govern the merging, formation and dying out of vapor embryos. Vapor embryo violates some predictions of classical bubble dynamics theory, it indicates that formation of vapor embryo may have a more microcopic nature than the formation of bubble. We compared systems under different temperatures to study the effects of superheating degree. The spinodal temperature of water at atmospheric pressure determined under our simulation condition is about 535 K, within the scope of available experimental results.
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