Sound-velocity measurements for HFC-134a and HFC-152a with a spherical resonator

A spherical acoustic resonator was developed for measuring sound velocities in the gaseous phase and ideal-gas specific heats for new refrigerants. The radius of the spherical resonator, being about 5 cm, was determined by measuring sound velocities in gaseous argon at temperatures from 273 to 348 K and pressures up to 240 kPa. The measurements of 23 sound velocities in gaseous HFC-134a (1,1,1,2-tetrafluoroethane) at temperatures of 273 and 298 K and pressures from 10 to 250 kPa agree well with the measurements of Goodwin and Moldover. In addition, 92 sound velocities in gaseous HFC-152a (1,1-difluoroethane) with an accuracy of ±0.01% were measured at temperatures from 273 to 348 K and pressures up to 250 kPa. The ideal-gas specific heats as well as the second acoustic virial coefficients have been obtained for both these important alternative refrigerants. The second virial coefficients for HFC-152a derived from the present sound velocity measurements agree extremely well with the reported second virial coefficient values obtained with a Burnett apparatus.Paper dedicated to Professor Joseph Kestin.     

Experimental surface tensions for HFC-32, HCFC-124, HFC-125, HCFC-141b,HCFC-142b,and HFC-152a

The surface tension of six alternative refrigerants, i.e., HFC-32 (CH, F, ). HCFC-124 (CHClFCF,), HFC-125 (CHF₂CF₃). HCFC-14lb ICH,CCI,F). HCFC-142b (CH₃CCIF₂), and HFC-152a (CH₃CHF₂), has been measured in the present study. The measurements were conducted under equilibrium conditions between the liquid and its saturated vapor. The differential capillary-rise method (DORM) used two glass capillaries, with inner radii of 0.3034 ± 0.0002 and 0.5717 ±0.0002 mm, respectively. Temperatures in the range from 270 to 340 K were considered. The accuracy of surface tension measurements is estimated to be within ±0.2 mN · m^–1. The temperatures are accurate to within ±20 mK. The temperature dependence of the resultant data were successfully represented by van der Waals' correlations to within ±(1.1 mN m^–1 for each substance. Available surface tension data are compared with the present data.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Thermal conductivity of gaseous HFC-134a,HFC-143a,HCFC-141b,and HCFC-142b

The thermal conductivity of new environmentally acceptable fluorocarbons HFC-134a (CH₂FCF₃), HFC-143a (CH₃CF₃), HCFC-141b (CH₃CCl₂F), and HCFC-142b (CH₃CCl₂F) in the gaseous phase has been measured in the temperature range 293–353 K at pressures up to 4 MPa. The thermal conductivity has been measured with a coaxial-cylinder cell on a relative basis. The apparatus was calibrated with He, Ne, Ar, Kr, N₂, CH₄, and SF₆ as reference fluids. The uncertainty of the experimental data obtained is estimated to be within 2% except for the uncertainty associated with the reference thermal-conductivity values. The excess thermal conductivity has been correlated satisfactorily as a function of density.     

Thermodynamic properties of seven gaseous halogenated hydrocarbons from acoustic measurements: CHClFCF3, CHF2 CF3, CF3 CH3, CHF2CH3, CF3CHFCHF2, CF3CH2CF3, and CHF2CF2CH2F

Measurements of the speed of sound in seven halogenated hydrocarbons are presented. The compounds in this study are 1-chloro-1,2,2,2-tetrafluoroethane (CHClFCF₃ or HCFC-124), pentafluoroethane (CHF₂ CF₃ or HFC-125), 1,1,1-trifluoroethane (CF₃CH₃ or HFC-143a), 1,1-difluoroethane (CHF₂CH₃ or HFC-152a), 1,1,1,2,3,3-hexafluoropropane (CF₃CHFCHF₂ or HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (CF₃CH₂CF₃ or HFC-236fa), and 1,1,2,2,3-pentafluoropropane (CHF₂CF₂CH₂F or HFC-245ca). The measurements were performed with a cylindrical resonator at temperatures between 240 and 400 K and at pressures up to 1.0 MPa. Ideal-gas heat capacities and acoustic virial coefficients were directly deduced from the data. The ideal-gas heat capacity of HFC-125 from this work differs from spectroscopic calculations by less than 0.2% over the measurement range. The coefficients for virial equations of state were obtained from the acoustic data and hard-core square-well intermolecular potentials. Gas densities that were calculated from the virial equations of state for HCFC-124 and HFC-125 differ from independent density measurements by at most 0.15%, for the ranges of temperature and pressure over which both acoustic and Burnett data exist. The uncertainties in the derived properties for the other five compounds are comparable to those for HCFC-124 and HFC-125.     

The thermal conductivity of CFC alternatives HFC-125 and HCFC-141b in the liquid phase

The liquid thermal conductivities of the CFC alternatives, HFC-125, and HCFC-141b measured by a transient hot-wire apparatus with one bare platinum wire are reported in the temperature ranges from 193 to 333 K (HFC-125, CHF₂, CF₃) and from 193 to 393 K (HCFC-141b,CCI₂F-CF₃), in the pressure ranges from 2 to 30 MPa (HFC-125) and from 0.1 to 30 MPa (HCFC-141b), respectively. The results have been estimated to have an accurancy of ±0.5%. The liquid thermal conductives obtained have been correlated by a polynomial of temperature and pressure which can represent the experimental results within the standard deviations of 0.49% for HFC-125 and 0.46% for HCFC-141b, respectively.     

Surface Tension of 1,1,1-Trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), and Their Binary Mixture HFC-143a/227ea

The surface tension of 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-hepta-fluoropropane (HFC-227ea), and their binary mixture HFC-143a/227ea at 3 nominal mass fractions of 27.91%/72.09%, 49.44%/50.56%, and 74.11%/25.89% were measured in the temperature range from 253 to 333K using the differential capillary rise method (DCRM) under vapor-liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mNm^–1, respectively. The present data were used to develop a van der Waals-type surface tension correlation for pure HFC-143a and HFC-227ea. Correlations for pure HFC-143a and HFC-227ea were used to develop a surface tension correlation for the experimental data of the HFC-143a/227ea mixtures as a function of the mass fraction.     

Ideal-gas specific heat and second virial coefficient of HFC-125 based on sound-velocity measurements

The sound velocity in gaseous pentafluoroethane (HFC-125, CF₃CHF₂) has been measured by means of a spherical acoustic resonator, Seventy-two sound-velocity values were measured with an uncertainty of ±0.01% at temperatures from 273 to 343 K and pressures from 101 to 250 kPa. The ideal-gas specific heats and the second acoustic-virial coefficients have been determined on the basis of the Sound-velocity measurements. The second virial coefficients calculated from the present sound-velocity measurements agree with literature values which were determined fromPVT measurements by means of a Burnett method.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24 1994, Boulder, Colorado, U.S.A.     

Thermal conductivity of halogenated ethanes,HFC-134a,HCFC-123, and HCFC-141b

The gaseous thermal conductivity of three CFC alternatives, HFC-134a (1,1,1,2-tetrafluoroethane), HCFC-123 (1,1-dichloro-2,2,2-trifluoroethane), and HCFC-141b (1,1-dichloro-1-fluoroethane), has been measured in the temperature ranges 273–363 K (HFC-134a) and 313–373 K (HCFC-123, HCFC-141b) at pressures up to saturation. The measurements were performed with a new improved transient hot-wire apparatus. The uncertainty of the experimental data is estimated to be within 1%. The gaseous thermal conductivity obtained in this work together with the liquid thermal-conductivity data from the literature were correlated with temperature and density by an empirical equation based on the excess thermal-conductivity concept. The equation is found to represent the experimental results with average deviations of 2.5 % for HFC-134a, 0.75% for HCFC-123, and 0.55% for HCFC-141b, respectively.     

Measurements ofPVTx properties of refrigerant mixture HFC-32+HFC-125 in the gaseous phase

The experimental 156PVTx properties of an important binary refrigerant mixture, HFC-32 (difluoromethane)+HFC-125 (pentafluorethane), have been measured for three compositions, i.e., 50, 60, and 80 wt% HFC-32, by a constant-mass-method coupled with expansion procedure in an extensive range of temperaturesT from 320 to 440 K, of pressuresP from 1.8 to 5.3 M Pa, and of densities p from 50 to 124 kg · m^–3. The experimental uncertainties of the present measurements are estimated to be within ±7 mK in temperature, ±2 kPa in pressure, ±0.2% in density and ±0.02 wt% of HFC-32. The sample purities are 99.998 wt% for HFC-32 and 99.99 wt% for HFC-125. Seventy-eight second and third virial coeflicients for temperatures from 320 to 440 K have been determined by the present measurements.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Vapor–Liquid Equilibria of Alternative Refrigerants by Molecular Dynamics Simulations

Alternative refrigerants HFC-152a (CHF₂CH₃), HFC-143a (CF₃CH₃), HFC-134a (CF₃CH₂F), and HCFC-142b (CF₂ClCH₃) are modeled as a dipolar two-center Lennard–Jones fluid. Potential parameters of the model are fitted to the critical temperature and vapor–liquid equilibrium data. The required vapor–liquid equilibrium data of the model fluid are computed by the Gibbs–Duhem integration for molecular elongations L=0.505 and 0.67, and dipole moments *²=0, 2, 4, 5, 6, 7, and 8. Critical properties of the model fluid are estimated from the law of rectilinear diameter and critical scaling relation. The vapor–liquid equilibrium data are represented by Wagner equations. Comparison of the vapor–liquid equilibrium data based on the dipolar two-center Lennard–Jones fluid with data from the REFPROP database shows good-to-excellent agreement for coexisting densities and vapor pressure.     

Thermal Conductivity of HFC-32, HFC-125, and HFC-134a in the Solid Phase

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous.     

Viscosity of Gaseous HFC-143a (1,1,1-trifluoroethane) Under High Pressures

The viscosity of gaseous HFC-143a(1,1,1-trifluoroethane) was measured with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K and at pressures up to the saturated vapor pressure at each temperature under subcritical conditions or up to 9 MPa under supercritical conditions. Intermolecular potential parameters of HFC-143a for the extended corresponding states were determined from the viscosity data at 0.1 MPa. An empirical viscosity equation as functions of temperature and density is proposed to interpolate the present experimental results.     

Thermal conductivity of alternative refrigerants in the liquid phase

Measurements ofthe thermal conductivity of five alternative refrigerants. namely, difluoromethane HFC-321. pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichloropentafluoropropanes (HCFC-225ca and HCFC-225cb). are carried out in the liquid phase, The range of temperature is 253–324 K for HFC-32, 257–305 K for HFC-125, 268–314 K for HFC-134a. 267–325 K for HCFC-225ca, and 286–345 K for HCFC-225cb, The pressure rank is from saturation to 30 MPa, The reproducibility of the data is better than 0.5% and the accuracy of the data is estimated to be of the order of 1%. The experimental results for the thermal conductivity ofeach substance are correlated by an equation which is a function of temperature and pressure. A short discussion is given to the comparison of the present results with literature values for HFC-125, The saturated liquid thermal conductivity values of HFC-32. HFC-125, and HFC-143a are compared with those of chlorodifluoromethane (HCFC-22) and tetrafluoroethane (HFC-134a) and it is shown that the value of HFC-32 is highest, while that of HFC-125 is lowest, among these substances, The dependence of thermal conductivity on number of fluorine atoms among the refrigerants with the same number of carbon and hydrogen atoms is discussed.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994. Boulder, Colorado. U.S.A.     

Thermodynamic Properties of HFC-227ea

The density and speed of sound in gaseous and liquid 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) have been studied by a -attenuation technique, an ultrasonic interferometer, and an isochoric piezometer method over the temperature range of 273 to 383K at pressures up to 3.5MPa. The purity of the samples used throughout the measurements are 99.99mol%. The pressures of the saturated vapor were measured over the same temperature range. The experimental uncertainties of the temperature, pressure, density, and speed of sound measurements were estimated to be within ±20mK, ±1.5kPa, ±0.2%, and ±(0.15–0.2)%, respectively. On the basis of the obtained data, the isobaric molar heat capacity of HFC-227ea was calculated for the ideal-gas state.     

Vapor+Liquid Equilibrium Measurements and Correlation of the Binary Refrigerant Mixtures Difluoromethane (HFC-32)+1,1,1,2,3,3-Hexafluoropropane (HFC-236ea) and Pentafluoroethane (HFC-125)+1,1,1,2,3,3-Hexafluoropropane (HFC-236ea) at 288.6, 303.2, and 318.2 K

Isothermal vapor–liquid equilibria (VLE) for the binary systems of difluoromethane (HFC-32)+1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and pentafluoroethane (HFC-125)+1,1,1,2,3,3-hexafluoropropane (HFC-236ea) were measured at 288.6, 303.2, and 318.2 K using an apparatus in which the vapor phase was recirculated through the liquid. The phase composition at equilibrium was measured by gas chromatography, based on calibration using gravimetrically prepared mixtures. Both systems show a slight deviation from Raoult's law. The uncertainties in pressure, temperature, and vapor- and liquid-phase composition measurements were estimated to be no more than ±1 kPa, ±0.02 K, and ±0.002 mol fraction, respectively. The data were analyzed using the Carnahan–Starling–DeSantis equation of state.     

Thermodynamic Properties of HFC-236ea

The density of gaseous and liquid 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) and the speed of sound in liquid HFC-236ea have been studied by a γ-attenuation technique, an ultrasonic interferometer, and an isochoric piezometer method over the temperature range of 263–423 K at pressures up to 4.05 MPa. The purity of the samples used throughout the measurements is 99.68 mol%. The pressures of the saturated vapor were measured over the same temperature range. The experimental uncertainties of the temperature, pressure, density, and speed-of-sound measurements were estimated to be within ±20 mK, ±1.5 kPa, ±(0.05–0.30)%, and ±(0.05–0.10)%, respectively.     

Prediction of the Vapor Pressure of Environmentally Acceptable Halocarbons1

The vapor pressure and its dependence on temperature of halocarbons for 0.002< p _R<1 have been analyzed in terms of universal behavior. Results for CFC-114, HCFC-123, HCFC-141b, HCFC-142b, HCFC-143a, HFC-23, HFC-32, HFC-134, HFC-125, HFC-134a, and HFC-152a for reduced temperatures between 0.55 and 1.0 show that the reduced vapor pressure can be expressed as a function of 1–T _R by a Padé approximant. Deviations of the correlated data from the universal function do not amount to more than ±0.06 MPa, with an average deviation of 0.025 MPa. Predictions of the saturation vapor pressures of HCFC-124, HCFC-225ca, and HCFC-225cb, which are the systems used to test the capability of this scheme, agree within 0.025 MPa, that is, within the accuracy of the corresponding states correlation. However, for HFC-236ea, the deviations are as large as –0.07 MPa. The present scheme can be used to calculate the Pitzer acentric factor, and an average value of =0.269±0.015 is obtained for all the fluids.     

An Experimental Study of <Emphasis Type="Italic">pVTx</Emphasis> Properties for Binary Mixtures of HFC-32 and HFC-125

An experimental study of the pressure-volume-temperature-composition pVTx properties for binary mixtures of HFC- 32(CH₂F₂) and HFC-125(C₂HF₅) was conducted in the range of temperatures from 343 to 423 K, pressures from 4.0 to 15.6 MPa, densities from 485 to 491 kg·m^–3, and compositions from 0.05 to 0.90 mole fraction of HFC-32, with uncertainties of 4.4 mK, 1.6 kPa, 0.02% , and 0.0004 mole fraction, respectively. The available experimental data for pVTx properties of binary mixtures of HFC-32 and HFC-125 have been compared with the equation of state developed by Tillner-Roth et al. From the critical evaluation, this equation of state should be revised in the range of low mole fractions of HFC-32.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

Calculation of second virial coefficients and gaseous viscosities of the refrigerants HFC-32 (CH2 F2), HFC-23 (CHF3), and HCFC-22 (CHC1F2)

The second virial coefficients of refrigerants HFC-32 (CH₂F₂), HFC-23 (CHF₃), and HCFC-22 (CHC1F₂) have been correlated on the bisis of site site model potential and have been compared with experimental results. The molecular interactions consisted of repulsion dispersion and electrostatic parts. From the site site potentials adjusted to the experimental second virial coefficients, spherically averaged potentials have been determined and a subsequent calculation of gaseous viscosity has been carried out. Agreement between measured and calculated values of second virial coellicients and gaseous viscosity is satisfactory. Calculated values of second virial coefficients and gaseous viscosity beyond available experimental data, therefore. can be assumed as a reliable extrapolation to lower and higher temperatures.     

Phase Equilibria of CFC Alternative Refrigerant Mixtures: 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea)+Difluoromethane (HFC-32), +1,1,1,2-Tetrafluoroethane (HFC-134a), and +1,1-Difluoroethane (HFC-152a)

Isothermal vapor–liquid equilibria were measured for the binary systems difluoromethane (HFC-32)+1,1,1,2,3,3,3-heptafluoropropane (HFC-22ea) and 1,1-difluoroethane (HFC-152a)+1,1,1,2,3,3,3-heptafluoropropane at 283.15 and 303.15 K and 1,1,1,2-tetrafluoroethane (HFC-134a)+1,1,1,2,3,3,3-heptafluoropropane at 303.15 and 323.15 K in an apparatus in which both phases were recirculated. The experimental data were correlated with the Peng–Robinson equation of state using the Wong–Sandler mixing rules. Azeotropic behavior has not been found in any of the three mixtures.