A fundamental equation of state for the Helmholtz free energy of R 134a (1,1,1,2tetrafluoroethane) is presented which is valid for temperatures between 170 K and 455 K and pressures up to 70 MPa. It is based on the most accurate measurements of pressuredensity-temperature (P ,p,T), speed of sound, heat capacity, and vapor pressure which are currently available. A linear regression analysis and a non-linear least squares fitting technique, based on the selected measurements, were used to determine the structure of the fundamental equation of state and the values of its 21 coefficients. The equation represents nearly all selected experimental data within their estimated accuracy with the exception of heat capacities and speed of sound in the region close to the critical point. Typica1 accuracies are ±0.05% for density, ±0.02% for the vapor pressure or ::to.5 and ±1 % for the heat capacity. This equation of state has been compared to equations established by other research groups by Annex 18 of the International Energy Agency (lEA) and has been selected as an international standard f011l1ulation for the thermodynamic properties of R 134a by this group.

A thermodynamic model incorporating a fundamental equation of state for the Helmholtz free energy of the mixture ͕waterϩammonia͖ is presented which covers the thermodynamic space between the solid-liquid-vapor boundary and the critical locus. It is also valid in the vapor and liquid phases for pressures up to 40 MPa. It represents vapor-liquid equilibrium properties with an uncertainty of Ϯ0.01 in liquid and vapor mole fractions. Typical uncertainties in the single-phase regions are Ϯ0.3% for the density and Ϯ200 J mol Ϫ1 for enthalpies. Details of the data selection and the optimization process are given. The behavior of the fundamental equation of state is discussed in all parts of the thermodynamic space.

A fundamental equation of state for the Helmholtz free energy of R-32 ͑difluo-romethane͒ is presented which is valid from the triple point at 136.34 K to 435 K and pressures up to 70 MPa. It is based on accurate measurements of pressure-densitytemperature (p, ,T), speed of sound, heat capacity, and vapor pressure currently available. New values for the isobaric heat capacity c p ‫ؠ‬ of the ideal gas calculated from spectroscopic data taking into account also first order anharmonicity corrections are presented. The Helmholtz free energy equation of state has 19 coefficients and represents all selected experimental data within their estimated accuracy with the exception for heat capacities and speed of sound in the region close to the critical point. Typical uncertainties are Ϯ0.05% for density, Ϯ0.02% for the vapor pressure and Ϯ0.5%-1% for the heat capacity. This equation of state has been compared to equations developed by other research groups by Annex 18 of the International Energy Agency and has been selected as an international standard formulation for the thermodynamic properties of R-32 by this group.

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