Vapour-liquid equilibrium of ternary mixtures of the refrigerants R125, R143a and R134a

Apart from ternary mixtures of R32 with R125 and R134a, similar mixtures with R143a instead of R32 are discussed as alternatives to the widely used refrigerants R22 and R502. In the present work, the phase equilibrium of such ternary mixtures is described by simple cubic equations of state which are based only on experimental data for the pure substances and for a nearly equimolar mixture of every binary system.In addition to previous experimental investigations the critical properties and the saturation pressure were measured for pure R143a and for nearly equimolar mixtures of the binary systems and . The temperature ranged from −70°C up to the respective critical point. The validity of the resulting equations of state for ternary mixtures of R125, R143a and R134a is confirmed by comparison with experimental results of the vapour-liquid equilibrium for a mixture with about 17mol% of R125 and R143a, respectively, and about 66mol% of R134a.     

Thermodynamic properties of R32 + R134a and R125 + R32 mixtures in and beyond the critical region

A parametric crossover equation of state for pure fluids is adapted to binary mixtures. This equation incorporates scaling laws asymptotically close to the critical point and is transformed into a regular classical expansion far away from the critical point. An isomorphic generalization of the law of corresponding states is applied to the prediction of thermodynamic properties and the phase behavior of binary mixtures over a wide region around the locus of vapor-liquid critical points. A comparison is made with experimental data for pure R32, R 125 and R 134a, and for R32 + R 134a and R 125 + R32 binary mixtures. The equation of state yields a good representation of thermodynamic property data in the range of temperatures 0.8T_c(x) ≤ T ≤ 1.5T_c(x) and densities 0.35 ?_c(x) ≤ ? ≤ 1.65?_c(x).     

Thermodynamic Properties of Mixtures of R-32, R-125, R-134a, and R-152a

A mixture model explicit in Helmholtz energy has been developed that is capable of predicting thermodynamic properties of refrigerant mixtures containing R-32, R-125, R-134a, and R-152a. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real gas) contribution, and the contribution from mixing. The contribution from mixing is given by a single equation that is applied to all mixtures used in this work. The independent variables are the density, temperature, and composition. The model may be used to calculate thermodynamic properties of mixtures, including dew and bubble point properties and critical points, generally within the experimental uncertainties of the available measured properties. It incorporates the most accurate published equation of state for each pure fluid. The estimated uncertainties of calculated properties are ±0.25% in density, ±0.5% in the speed of sound, and ±1% in heat capacities. Calculated bubble point pressures are generally accurate to within ±1%.     

Equations of state for the thermodynamic properties of R32 (difluoromethane) and R125 (pentafluoroethane)

Thermodynamic properties of difluoromethane (R32) and pentafluoroethane (R125) are expressed in terms of 32-term modified Benedict-Webb-Rubin (MBWR) equations of state. For each refrigerant, coefficients are reported for the MBWR equation and for ancillary equations used to fit the ideal-gas heat capacity and the coexisting densities and pressure along the saturation boundary. The MBWR coefficients were determined with a multiproperty fit that used the following types of experimental data: PVT: isochoric, isobaric, and saturated-liquid heal capacities; second virial coefficients; and properties at coexistence. The respective equations of stale accurately represent experimental data from 160 to 393 K and pressures to 35 MPa for R32 and from 174 to 448 K and pressures to 68 MPa for R125 with the exception of the critical regions. Both equations give reasonable results upon extrapolation to 500 K and 60 MPa. Comparisons between predicted and experimental values are presented.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado. U.S.A.     

A simple set of equations of state for process calculations and its application to R134a and R152a

This paper reports a useful set of equations which enables the consistent and reliable calculation of thermodynamic properties. This set of equations consists of a vapour pressure equation, an equation for the gas phase p, v, T properties, an equation giving the saturated liquid densities and an equation for the specific heat capacity in the ideal gas domain. These equations are of a simple structure because the critical region is excluded. Therefore, for a preliminary investigation only few experimental data points are required for parameter regression, which makes this set of equations suitable for ‘new’ refrigerants. The relationships for enthalpy and entropy are derived from these equations and evaluation procedures are summarized. Examples are given for the refrigerants R134a and R152a.     

Solubility of nitrogen in one-component refrigerants: Prediction by PC-SAFT EoS and a correlation of Henry’s law constants

Even small amount of non-condensable gas - mostly air or nitrogen - present inside a compression refrigerating circuit may decrease the efficiency of the cooling system. So far, a quantitative assessment of the effect of dissolved gases on the cooling circuit performance is hindered by unavailability of suitable thermodynamic models. In this study, we analyzed the solubility of nitrogen in the following refrigerants: hydrochlorofluorocarbons (HCFC) R22, R123, R124; hydrofluorocarbons (HFC) R23, R32, R125, R134a; perfluorocarbons (PFC) R14, R116, R218, R-3-1-10; and hydrocarbons (HC) R290, R600a. Perturbed-Chain (PC) Statistical Associating Fluid Theory (SAFT) and its modification for polar fluids PCP-SAFT were used to model the temperature dependence of the Henry’s law constant of nitrogen. A simple correlation of the Henry’s law constants valid over large temperature ranges was developed, suitable for assessment of the adverse effects of dissolved nitrogen (and approximately air) on the performance of compression cooling systems.     

Transport properties of refrigerants R32, R125, R134a, and R125+R32 mixtures in and beyond the critical regionPropriétés de transport des frigorigènes R32, R125, R134a et des mélanges de R125+R32 dans et au-delà la région critique

A practical representation for the transport coefficients of pure refrigerants R32, R125, R134a, and R125+R32 mixtures is presented which is valid in the vapor–liquid critical region. The crossover expressions for the transport coefficients incorporate scaling laws near the critical point and are transformed to regular background values far away from the critical point. The regular background parts of the transport coefficients of pure refrigerants are obtained from independently fitting pure fluid data. For the calculation of the background contributions of the transport coefficients in binary mixtures, corresponding-states correlations are used. The transport property model is compared with thermal conductivity and thermal diffusivity data for pure refrigerants, and with thermal conductivity data for R125+R32 mixtures. The average relative deviations between the calculated values of the thermal conductivity and experimental data are less than 4–5% at densities ρ0.1ρ_c and temperatures up to T=2T_c.