A non-equilibrium molecular dynamics study of subcritical, supercritical and transcritical mixing of liquid-gas systems

A non-equilibrium molecular dynamics (NEMD) simulation method has been developed to simulate mixing of a liquid with a vapor and identify the characteristics of the liquid-vapor interface in the mixing process. Our results show that for the case of subcritical mixing, local phase equilibrium is established, and saturated liquid and saturated vapor are formed on either side of the interface at the prevailing saturation temperature that is fixed by the pressure of the system independent of the temperature difference across the interface. For transcritical mixing, significant clustering of molecules is found at the "transitional diffuse" interface. We found that the local density and local temperature of the transcritical interface can be directly mapped to the near critical region of the Ar/Ar and Kr/Ar vapor-liquid phase diagram. Finally, for the case of supercritical mixing, our simulations show a gradual change of density consistent with diffusion-controlled fluid mixing. (C) 2019 Elsevier Ltd. All rights reserved.