Conference Year
2016
Keywords
Equation of state, Low GWP refrigerant, R-1123, Thermodynamic property, Vapor pressure
Abstract
A first fundamental equation of state explicit in the Helmholtz energy is presented for trifluoroethylene (R-1123). Much attention has been given to this novel refrigerant due to its preferable characteristics for working fluids in residential air conditioners. The independent variables of the equation of state are temperature and density. All thermodynamic properties can be derived as derivatives of the Helmholtz energy. The equation of state is composed of two parts; one is the ideal-gas part representing ideal-gas properties, and the other is the residual part corresponding to the influence of intermolecular forces. The ideal-gas part is analytically formulated from a correlation for the ideal-gas isobaric heat capacity. The correlation comes from sound speed data in the vapor phase. The residual part is empirically determined from experimental data for the critical parameters, vapor pressures, vapor sound speeds, and liquid and vapor densities, including those at saturation. Following recent trends in the development of accurate equations of state, a functional form that includes Gaussian bell-shaped terms was optimized with the use of nonlinear least-squares fitting to the experimental data. Numerous thermodynamic constraints were applied to control the slope and curvature of derived properties from the equation of state. The equation is valid for temperatures from 273 K to 450 K and for pressures up to 10 MPa. Typical uncertainties over the range of validity are 0.1 % for vapor pressures, 0.1 % for liquid densities, and 0.5 % for vapor densities, except in the critical region where larger deviations up to about 2 % are observed in densities. At temperatures below 300 K, deviations in vapor pressures are larger due to higher experimental uncertainties. The equation shows reasonable extrapolation behavior in regions away from the experimental data. Although the equation is based on limited experimental data, it is the best currently available for the calculation of thermodynamic properties for R-1123. The equation of state will be incorporated in the ongoing development of a multi-fluid mixture model for the R-32/1123 mixture.