Helmholtz Free Energy Models for the Environment Friendly Refrigerant R290+R1234ze(E)/R1234yf

Helmholtz free energy equations of state for R290+R1234ze(E) and R290+R1234yf mixtures are presented in this work. The equations of state are based on the multi-uid approximations model, where Helmholtz energy of the mixture α is expressed as a function of density, temperature and composition. It consists of two parts α₀ and α_r, which represent the properties of ideal-gas mixtures and the residual mixture behavior, respectively. The first part α₀ can be determined from the most accurate equations of state for each pure uid, while the second part α_r are determined by fitting the available experimental vapour{liquid phase equilibrium data, gaseous pρT data and saturated liquid pρT data. In this work, 11 mixture rules (combinations of reducing functions and departure functions) are employed to describe the thermophysical properties of the considered binary mixtures and optimal Helmholtz free energy equations of state are established. The calculated average absolute relative deviations are within 0.5% for pressure and 0.3% for density.