New Equation for Vapor Pressures of Difluoromethane (HFC-32)

Critically evaluated experimental vapor-pressure data sets supplemented with calculated data for low-temperature region were used in the development of vapor-pressure equations. The optimum number of terms, coefficients, and exponents of the Wagner-type equation were derived by means of the Setzmann–Wagner program OPTIM based on the combination of the stepwise regression analysis and evolutionary optimization method. Equations were checked by the reduced enthalpy of vaporization criterion derived from the Clausius–Clapeyron equation and specific volume of ideal gas. An equation developed using 261 experimental data points and low-temperature data calculated by Lüddecke and Magee gives an RMS deviation of 0.102%; a second equation based on the same experimental data and low-temperature data calculated by Tillner-Roth gives an RMS deviation of 0.101% from experimental points. The triple-point pressure extrapolated to the measured temperature T _tp = 136.34 K is discussed. Comparisons with vapor pressure equations by Outcalt and McLinden, Duarte-Garza and Magee. and Kubota et al. are also given.     

Measurements of the Thermal Conductivity of HFC-32 (Difluoromethane) in the Temperature Range from 300 to 465 K at Pressures up to 50 MPa

New measurements of the thermal conductivity of HFC-32, made in a coaxial cylinder cell operating in steady state, are reported. The measurements were performed along several quasi-isotherms between 300 and 465 K in both the liquid and the vapor phases. The pressure ranged from 0.1 to 50 MPa. Based on the experimental data, a background equation is provided to calculate the thermal conductivity outside the critical region as a function of temperature and density. A careful analysis of the various sources of experimental errors leads to an estimated uncertainty of ±1.5%. Comparisons between calculated and experimental values from the literature are presented.     

Determination of Second Virial Coefficients and Virial Equations of R-32 (Difluoromethane) and R-125 (Pentafluoroethane) Based on Speed-of-Sound Measurements

The second virial coefficients, B, for difluoromethane (R-32, CH₂F₂) and pentafluoroethane (R-125, CF₃CHF₂) are derived from speed-of-sound data measured at temperatures from 273 to 343 K with an experimental uncertainty of ±0.0072%. Equations for the second virial coefficients were established, which are valid in the extensive temperature ranges from 200 to 400 K and from 240 to 440 K for R-32 and R-125, respectively. The equations were compared with theoretically derived second virial coefficient values by Yokozeki. A truncated virial equation of state was developed using the determined equation for the virial coefficients. The virial equation of state represents our speed-of-sound data and most of the vapor PT data measured by deVries and Tillner-Roth within ±0.01 and ±0.1%, respectively.     

Measurements of PVTx Properties for Binary Mixtures of HFC-32 (CH2F2) and HFC-134a (CH2FCF3)

An experimental study of pressure–volume–temperature–composition (PVTx) properties for binary mixtures of HFC-32 and HFC-134a was conducted in the range of temperatures from 243 to 473 K, pressures up to 16.7 MPa, densities from 9.5 to 1065 kg·m^–3, and compositions from 0.39 to 0.89 mol fraction of HFC-32, with uncertainties of 8 mK, 1.7 kPa, 0.04%, and 0.001 mol fraction, respectively. A constant-volume method was used for the present measurements either with a spherical vessel approximately 270 cm³ in its inner volume or with a cylindrical vessel approximately 138cm³ in its inner volume. The present data were compared with the Piao equation of state for this substance.     

Thermophysical Properties of 1,1,1,3,3-Pentafluorobutane (R365mfc)

This paper presents an experimental study on various thermophysical properties of a new fluoroalkane, 1,1,1,3,3-pentafluorobutane (R365mfc). The thermal conductivity of R365mfc was measured in the liquid phase near saturation conditions at temperatures between 263 and 333 K using a parallel plate instrument with an uncertainty of less than ±5%. For the measurement of the saturated liquid density between 273 and 353 K, a vibrating tube instrument was used. The uncertainty of the density measurements is less than ±0.1%. In addition, experimental data have been obtained for R365mfc under saturation conditions over a wide temperature range from about 253 to 460 K using light scattering techniques. Light scattering from the bulk fluid has been applied for measuring both the thermal diffusivity and the sound speed in the liquid and vapor phases. Light scattering by surface waves on a horizontal liquid–vapor interface has been used for the simultaneous determination of the surface tension and kinematic viscosity of the liquid phase. With the light scattering techniques, uncertainties of less than ±1.0, ±0.5, ±1.0, and ±1.2% have been achieved for the thermal diffusivity, the sound speed, the kinematic viscosity, and the surface tension, respectively.     

Thermodynamic Properties of Trifluoroiodomethane (CF13I)1

Studies of the thermodynamic properties of trifluoroiodomethane (CF₃I) are presented in this paper. The vapor–liquid coexistence curve of CF₃I was measured by visual observation of the meniscus. The critical temperature and the critical density of CF₃I were determined by considering not only the level where the meniscus disappeared but also the intensity of the critical opalescence. The correlation of the saturated density in the critical region was developed, and the exponent of the power law was determined. Correlations of the saturated vapor and liquid densities and the enthalpy of vaporization for CF₃I were also developed. The vapor pressure of CF₃I was measured at temperatures ranging from below the normal boiling point to the critical point, and a vapor pressure equation for CF₃I was developed, from which the normal boiling point of CF₃I was determined. The gaseous PVT properties of CF₃I were measured with a Burnett/isochoric method, and a gaseous equation of state for CF₃I was developed. The speed of sound of gaseous CF₃I was measured with a cylindrical, variable-path acoustic interferometer operating at 156.252 kHz, and the ideal-gas heat capacity and second acoustic virial coefficient were calculated. A correlation of the second virial coefficient for CF₃I was obtained by a semiempirical method using the square-well potential for the intermolecular force and was compared with the result based on PVT measurements. The surface tension of CF₃I was measured with a differential capillary rise method (DCRM), and the temperature dependence of the results was successfully represented to within ±0.13 mN·m^–1 using a van der Waals correlation.     

Thermophysical Properties of a Refrigerant Mixture of R365mfc (1,1,1,3,3-Pentafluorobutane) and Galden<Superscript>®</Superscript> HT 55 (Perfluoropolyether)

This work presents a comprehensive experimental study of various thermophysical properties of an azeotropic refrigerant mixture of 65 mass% R365mfc (1,1,1,3,3-pentafluorobutane) and 35 mass% Galden^? HT 55 (perfluoropolyether). Light scattering from bulk fluids has been applied for measuring both the thermal diffusivity and the speed of sound in the liquid and vapor phases under saturation conditions, between 293 K and the liquid–vapor critical point at 450.7 K. Furthermore, the speed of sound has been measured for the superheated-vapor phase along nine isotherms, between 393 and 523 K and up to a maximum pressure of about 2.5 MPa. For temperatures between 253 and 413 K, light scattering by surface waves on a horizontal liquid–vapor interface has been used for simultaneous determination of the surface tension and kinematic viscosity of the liquid phase. With light scattering techniques, uncertainties of less than ±2.0%, ±0.5%, ±1.5%, and ±1.5% have been achieved for the thermal diffusivity, sound speed, kinematic viscosity, and surface tension, respectively. In addition to vapor-pressure measurements between 304 and 448 K, the density was measured between 273 and 443 K using a vibrating-tube method. Here, measurements have been performed in the compressed- and saturated-liquid phases with uncertainties of ±0.3% and ±0.1%, respectively, as well as for the superheated vapor up to a maximum pressure of about 3 MPa with an uncertainty between ±0.3% and ±3%. Critical-point parameters were derived by combining the data obtained by different techniques.