Thermodynamic analysis of molecular dynamics simulation of evaporation and condensation

When a gas or vapour is flowing through a microchannel, the system can become too small for the Navier-Stokes approach to be valid: the Knudsen number becomes too large. Modelling techniques that include the particle nature of the fluids should be used. A particle simulation method is Molecular Dynamics (MD). MD-simulations have been shown to give accurate results both in the gas phase and in the liquid phase. In a two-phase flow, the phase transition between the liquid phase and gas phase is important.In MD simulations, this phase transition can be modeled. It is important that in the MD simulations, the phase at transition is modeled thermodynamically correct. The goal of this research is to develop a method to validate particle-based models, such as MD, by comparing simulation results to experimental results. This is done by simulating an equilibrium situation of evaporation and condensation. After an equilibrium situation has been established, the following properties are calculated: Temperature profile, density profile, pressure profile and enthalpy. The analysis for Molecular Dynamics was performed, using Argon-particles. After the simulations were run and shown to be in equilibrium, the thermodynamic properties are analyzed and shown to agree with experimental results from literature for the liquid and vapour phase. It is shown that the cut-off radius in Molecular Dynamics simulations should be chosen carefully: when the potential energy function is cut off after more than 4.5 molecular diameters,the simulation results for density, pressure and enthalpy agree with experimental results.