New functional forms have been developed for multiparameter equations of state for non- and weakly polar fluids and for polar fluids. The resulting functional forms, which were established with an optimization algorithm which considers data sets for different fluids simultaneously, are suitable as a basis for equations of state for a broad variety of fluids. The functional forms were designed to fulfil typical demands of advanced technical application with regard to the achieved accuracy. They are numerically very stable and their substance-specific coefficients can easily be fitted to restricted data sets. In this way, a fast extension of the group of fluids for which accurate empirical equations of state are available is now possible. This article deals with the results found for the polar fluids CFC-11 (trichlorofluoromethane), CFC-12 (dichlorodifluoromethane), HCFC-22 (chlorodifluoromethane), HFC-32 (difluoromethane), CFC-113 (1,1,2-trichlorotrifluoroethane), HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane), HFC-125 (pentafluoroethane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-143a (1,1,1-trifluoroethane), HFC-152a (1,1-difluoroethane), carbon dioxide, and ammonia. The substance-specific parameters of the new equations of state are given as well as statistical and graphical comparisons with experimental data. General features of the new class of equations of state such as their extrapolation behavior or their numerical stability and results for non- and weakly polar fluids have been discussed in preceding articles.

Equations of state for technical applications. III. Results for polar fluids

A modified Benedict–Webb–Rubin (MBWR) equation of state has been developed for Refrigerant 123 (2,2‐dichloro‐1,1,1‐trifluoroethane) based on recently measured thermodynamic property data and data available from the literature. Single‐phase pressure‐volume‐temperature (PVT), heat capacity, and sound speed data, as well as second virial, vapor pressure, and saturated liquid and saturated vapor density data, were used with multiproperty linear least squares fitting techniques to fit the 32 adjustable coefficients of the MBWR equation. Coefficients for the equation of state and for ancillary equations representing the vapor pressure saturated liquid and saturated vapor densities, and ideal gas heat capacity are given. While the measurements cover differing ranges of temperature and pressure, the MBWR formulation is applicable along the saturation line and in the liquid, vapor, and supercritical regions at temperatures from 166 to 500 K with pressures to 40 MPa and densities to 11.6 mol/L (1774 kg/m3). This formulation has been selected as an international standard based on an evaluation of the available equations of state by a group working under the auspices of the International Energy Agency.

An International Standard Equation of State for the Thermodynamic Properties of Refrigerant 123 (2,2‐Dichloro‐1,1,1‐Trifluoroethane)

We have developed a predictive corresponding states model for the thermophysical properties of pure refrigerants and refrigerant mixtures. The bulk phase properties such as the density, enthalpy and entropy are predicted using the principle of extended corresponding states, incorporating a recent 32-term modified Benedict-Webb-Rubin correlation for the R134a (1,1,1,2-tetrafluoroethane) reference fluid. This theoretically based model uses shape factors to ensure conformality among the various components. A correlation for the shape factors was found by mapping saturation boundaries of the fluids of interest onto the reference fluid and then fitting the results to an empirical correlation. In this work we present the coefficients for density-independent shape-factor correlations for 21 refrigerants, and a set of universal coefficients that can be used with any refrigerant given only the critical parameters and the acentric factor. We show comparisons with experimental density data for each of the 21 refrigerants. We also demonstrate the use of generalized coefficients for shape factors where only the critical parameters and acentric factors are known. In addition, we present comparisons of the volume prediction for two binary refrigerant mixtures and one ternary refrigerant mixture.

A predictive extended corresponding states model for pure and mixed refrigerants including an equation of state for R134a

Vle have developed a predictive corresponding states model for the thermo· physical properties of pure refrigerants and refrigerant mixtures. The bulk phase properties such as the density, enthalpy and entropy are predicted using the prin· ciple of extended corresponding states. This theoretically based model uses shape factors to insure conformality among the various components and R134a is used as the reference fluid. The shape factors are found by mapping saturation boundaries of the fluids of interest onto the reference fluid. In the case where no saturation data are available, the shape factors are predicted. In addition to equilibrium properties, a one-fluid corresponding states model is used to predict the viscosity and thermal conductivity. Phase equilibria is predicted using a Peng-Robinson equation of state. The corresponding states model is contained in an interactive microcomputer program, PROZPER, (PRoperties of OZone Protecting Environmentally acceptable Refrigerants). The program performs various vapor-liquid equilibria calculations-dew point and bubble point pressures and temperatures, isothermal, isenthalpic and isentropic flashes-and gives the bulk phase properties (such as density, enthalpy, entropy, Joule-Thomson coefficient, Cp, Cp/Cv, sound speed, viscosity and thermal conductivity) of the coexisting phases. Calculations may be performed on pure fluids or on mixtures of up to 20 components. A built-in database contains many common refrigerants including fully-halogenated CFC's (for example Rll, Rl14, R12 and R13) as well as environmentally acceptable alter· natives (such as R123, R134a and others). In addition, the program can "learn" new components using only a minimum amount of information-the molecular weight, the normal boiling point and the critical parameters of the chemical species. Additional information such as vapor pressures, saturated liquid densities, saturated liquid thermal conductivities and viscosities may be input to improve the predictive capability of the model.

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A Predictive Extended Corresponding States Model for Pure and Mixed Refrigerants

New equations for the thermal conductivity and the viscosity of R134a that are valid in a wide range of pressures and temperatures are presented. They were obtained through a theoretically based, critical evaluation of the available experimental data, which showed considerable inconsistencies between data sets, in particular in the vapor phase. In the critical region the observed enhancement in the thermal conductivity is well represented by a crossover model for the transport properties of fluids. Since thermodynamic properties enter into the calculation of the critical enhancement of the transport properties, a new fundamental equation for the critical region was developed also.

Transport properties of 1,1,1,2-tetrafluoroethane (R134a)

The isobaric heat capacity, C p , of liquid HFC-134a, which is a prospective alternative to CFC-12, has been measured by using a flow calorimeter. The C p of saturated liquid, C p ', has been determined on the basis of the data measured in the compressed liquid phase, and a correlation of C p ' has also been developed

Atsushi Saitoh

Papers

Isobaric heat capacity data for liquid HFC-134a