Evaporation of Ar/Kr mixtures on platinum surface: A molecular dynamics study

The evaporation is a typical heat and mass transfer process, which is important in nature and industry. Here, the molecular dynamics simulation was employed to investigate the evaporation of five fluid samples (pure Ar, pure Kr and Ar/Kr mixtures with molar ratio Ar:Kr=1:3, Ar:Kr=1:1 and Ar:Kr=3:1) on the platinum surface. The colligative properties of mixtures led to the melting of Ar/Kr mixtures (Ar:Kr=1:1, Ar:Kr=3:1) at 70 K, below the triple point of Ar. Meanwhile, the other systems were frozen as the solid state under the same situation. The Pt surface with 90 K, over the boiling point of Ar, triggered the evaporation of Ar atoms in all the systems while the Kr atoms remained condense state. The Kr atoms were found notably evaporated when the Pt surface heated to 120 K, near the boiling point of Kr. The existence of Kr could reduce the evaporation of Ar atoms, especially when the mole ratio of Ar:Kr in the mixture is 1:1. This is because the Ar:Kr=1:1 system can effectively reduce the temperature of the gas-liquid interface. The temperature of fluid samples decreased with the increasing distance between the Pt atoms and fluid atoms. The reason was that the evaporated atoms could take thermal energy away from the condensed films. In addition, the Ar and Kr atoms which closed to Pt surface hardly changed during the evaporation for the strong attractive force from the Pt substrate.