Thermodynamic properties of supercritical carbon dioxide using molecular dynamics simulation

Abstract

Supercritical carbon dioxide (scCO₂) is widely used in various industrial and energy systems, exerting profound influences on the operational efficiencies of these devices through changing their physical properties. Molecular dynamics (MD) simulation is a powerful tool to calculate the thermodynamic properties and larger simulation scales are essential for scCO₂ characterized by significant local inhomogeneities. In this study, large-scale MD simulation was used to obtain the thermodynamics properties including density, isobaric heat capacity, isochoric heat capacity, volume expansion coefficient, isothermal compression coefficient, and Joule–Thomson coefficient of scCO₂ at temperatures of 300–900 K and pressures of 7.3773–20 MPa, with average relative errors of 3.76%, 3.93%, 3.11%, 5.76%, 7.07%, and 14.24%, respectively. The corresponding Widom lines of these thermodynamic properties were obtained, and they formed an approximately fan-shaped area called “Widom line region.” The expressions of the Widom lines were fitted with R² of above 97.48%, well guiding the operation of scCO₂ systems.