Molecular Dynamics Simulations Of Evaporation Behaviors For Suspended Nanodroplets

The evaporation of suspended droplets is a common natural phenomenon, existing widely in chemical engineering, pharmaceutics and combustion and so on. In the process of spray drying, the evaporation rate of suspended droplets is the key to the efficiency of drying equipment. In addition, burning degree of suspended flue droplets in the direct injection engine of gasoline, affected by evaporation rate, can directly influence the amount of energy and the ingredients of generated gases. Actually, the phenomenon of evaporation occurs in the form of a group of droplets, while studying the evaporation of a single droplet is foundational. The study of a single droplet evaporation mainly concentrated on macroscopic droplets through experimental methods. Many macroscopic quantities are based on continuity hypothesis, but when the diameter of droplet reaches to nanoscale, continuity hypothesis is no longer valid. Furthermore, the existing experimental devices can't do the corresponding researches. With the rapid development of computer technology, studying evaporation process of nanometer droplets using the method of simulations becomes a reality. In this paper, molecular dynamics simulations using LAMMPS are applied to research the evaporation behaviors of suspended nanodroplets, including argon droplet, Ar-CH4) binary mixtures droplets and particle-laden droplets, providing preliminary evaporation theory of suspended nanodroplets.The results of simulations show that different types of spherical droplets almost keep spherical during the process of evaporation. The higher temperature of system is, the smaller the sphericity of the droplets becomes. The less atomic number of droplet is, the smaller the sphericity of the droplets becomes. The bigger mass fraction of metal particle in droplet is, the smaller the sphericity of the droplets becomes. Simulation parameters have different impact on the statistical quantities. The grid size mainly influences the density distribution, while the parameter of affecting the liquid molecules of droplets is mainly truncated radius. In general, the truncated radius is a vital parameter during the molecular dynamics simulations. As for the evaporation about droplets of pure argon, higher temperature of system and smaller initial diameter of droplets can lead to bigger evaporation rate. With respect to the droplets of mixture of argon and methane, the smaller the mole fraction of methane in droplets is, the bigger the evaporation rate becomes. Besides, the higher temperature of system and smaller initial diameter of mixture droplets can also result in bigger total evaporation rate. The existence of nitrogen in the gaseous phase has no effect on evaporation rate of droplets. For laden-particle droplets, the higher the temperature of system is, the bigger the evaporation rate of laden-particle droplets becomes. Evaporation rate becomes smaller slightly compared with droplets of pure argon.