Phase Behavior and Surface Tension for the Carbon Dioxide (CO₂), Difluoromethane (R32), and 1,1,1,2-Tetrafluoroethane (R134a) Mixtures: A Molecular Dynamics Study

Carbon dioxide (CO₂), as a natural working fluid, is blended with hydrofluorocarbons (HFCs) or hydrofluoroolefins (HFOs) that exhibit favorable thermodynamic properties. By modifying the mixture composition, the performance of the refrigeration system can be optimized in terms of efficiency and operational conditions. However, comprehensively evaluating the thermodynamic properties of CO₂-based mixtures through experimental measurements alone remains challenging due to the complexity, expense, and time involved. This highlights the critical necessity for advanced computational methods to enhance and extend experimental research. In this study, molecular dynamics (MD) simulations were employed to comprehensively investigate the vapor–liquid phase behaviors and surface tension properties of CO₂, R32, and R134a in their pure, binary, and ternary components, respectively. The MD results show good agreement with our previous Gibbs Ensemble Monte Carlo (GEMC) simulations and the experiment-derived correlations from REFPROP program, demonstrating the precision and dependability of the employed force field and molecular methodology. These findings validate that molecular simulation, when coupled with a well-parameterized potential energy function, can effectively characterize essential thermophysical properties and fill data gaps where experimental measurements are limited. The methodology provides a solid foundation for subsequent research on refrigerant mixture behavior and offers valuable insights for the optimization and design of thermal cycle systems.