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.     

Thermophysical Properties of Gaseous CF4 and C2F6 from Speed-of-Sound Measurements

A cylindrical resonator was employed to measure the sound speeds in gaseous CF₄ and C₂F₆. The CF₄ measurements span the temperature range 300 to 475 K, while the C₂F₆ measurements range from 210 to 475 K. For both gases, the pressure range was 0.1 MPa to the lesser of 1.5 MPa or 80% of the sample’s vapor pressure. Typically, the speeds of sound have a relative uncertainty of less than 0.01 % and the ideal-gas heat capacities derived from them have a relative uncertainty of less than 0.1%. The heat capacities agree with those determined from spectroscopic data. The sound speeds were fitted with the virial equation of state to obtain the temperature-dependent density virial coefficients. Two models for the virial coefficients were employed, one based on square-well potentials and the second based on a Kihara spherical-core potential. The resulting virial equations reproduce the sound-speed measurements to within 0.005 % and yield densities with relative uncertainties of 0.1% or less. The viscosity calculated from the Kihara potential is 2 to 11% less than the measured viscosity.     

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.     

Measurement of Speed of Sound with a Spherical Resonator: HCFC-22, HFC-152a, HFC-143a, and Propane

A spherical resonator and acoustic signal measurement apparatus have been designed and developed for measuring the speed of sound in the gaseous phase. The inner radius of the spherical resonator, being about 6.177 cm, was determined by measuring the speed of sound in gaseous argon at temperatures between 293 and 323 K and at pressures up to 200 kPa. Measurements of the speed of sound in four halogenated hydrocarbons are presented, the compounds are chlorodifluoromethane (CHClF₂ or HCFC-22), 1,1-difluoroethane (CH₃CHF₂ or HFC-152a), 1,1,1-trifluoroethane (CH₃CF₃ or HFC-143a), and propane (CH₃CH₂CH₃ or HC-290). Ideal-gas heat capacities and acoustic virial coefficients were directly deduced from the present data. The results were compared with those from other studies. In this work, the experimental uncertainties in temperature, pressure, and speed of sound are estimated to be less than ±14 mK, ±2.0 kPa, and ±0.0037%, respectively. In addition, equations for the ideal-gas isobaric specific heat capacity for HFC-152a, HFC-143a, and propane are proposed, which are applicable in temperature ranges 240 to 400 K for HFC-152a, 250 to 400 K for HFC-143a, 225 to 375 K for propane. The purities for each of the samples of HCFC-22, HFC-152a, HFC-143a, and propane are better than 99.95 mass%.     

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.     

Thermodynamic Properties of 1,1,1,2,3,3,3-Heptafluoropropane

A vapor pressure equation has been developed for 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) based on previous measurements from 202 to 375K, from which the boiling point of HFC-227ea was determined. Based on the previous pressure–volume–temperature (PVT) measurements in the gaseous phase for HFC-227ea, virial coefficients, saturated vapor densities, and the enthalpy of vaporization for HFC-227ea were also determined. The vapor pressure equation and the virial equation of state for HFC-227ea were compared with the available data. Based on the previous measurements of speed of sound in the gaseous phase for HFC-227ea, the ideal-gas heat capacity at constant pressure and the second acoustic virial coefficient of HFC-227ea were calculated. A correlation of the second virial coefficient for HFC-227ea was obtained by a semiempirical method using the square-well potential for the intermolecular force and was compared with results based on PVT measurements. A van der Waals-type surface tension correlation for HFC-227ea was proposed, based on our previous experimental data by the differential capillary rise method from 243 to 340K.     

Viscosity of Gaseous Mixtures of HFC-134a (1,1,1,2-Tetrafluoroethane)+HFC-32 (Difluoromethane)

This paper reports experimental results for the viscosity of gaseous mixtures of HFC-134a (1,1,1,2-tetrafluoroethane)+HFC-32 (difluoromethane). The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K. The viscosity was measured for three mixtures containing 25.00, 52.40, and 74.98 mole% HFC-134a in HFC-32. Experimental results for the viscosity at normal pressures show a minimum as plotted against mole fraction in the higher temperature region, which may be the first experimental observation of the minima for dilute binary gaseous mixtures of HFCs. The viscosity at normal pressures was analyzed with the extended law of corresponding states developed by Kestin et al., and the scaling parameters were obtained for unlike-pair interactions between HFC-32 and HFC-134a. The modified Enskog theory developed by Vesovic and Wakeham was applied to predict the viscosity for the binary gaseous mixtures under pressure. As for the calculation of pseudo-radial distribution functions in mixtures, a method based on the equation of state for hard-sphere fluid mixtures proposed by Carnahan–Starling was applied.     

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.     

The dilute-gas properties of some systems containing CO2

The SSR-MPA potential model is used to correlate and extrapolate the dilutegas properties of some systems containing CO₂. With parameters determined from a consistent set of second virial and Joule-Thomson data, the third virial coefficient of CO₂ as well as the second virial coefficients of various mixtures containing CO₂ can be predicted very well. The Mason-Monchik approximation fails for a complicated molecule such as CO₂, although at least a viscosity prediction of technical accuracy is obtained. If parameters fitted to the CO₂ viscosity are used, excellent predictions can be made for the viscosity of gaseous mixtures containing CO₂.     

Viscosity of Gaseous Mixtures of HFC-125+HFC-32

This paper reports experimental results for the viscosity of gaseous mixtures of HFC-125 (pentafluoroethane)+HFC-32 (difluoromethane). The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15K. The viscosity was measured for three mixtures (mole fraction of HFC-125 is 0.7498, 0.4998, or 0.2475). The viscosity at normal pressure was analyzed with the extended law of corresponding states developed by Kestin et al. and the scaling parameters were obtained for unlike-pair interactions between HFC-125 and HFC-32. The modified Enskog theory developed by Vesovic and Wakeham was applied to predict the viscosity for the binary gaseous mixtures under pressure. For the calculation of the pseudo-radial distribution function in mixtures, a method based on the Carnahan–Starling equation for the radial distribution function of hard sphere mixtures is proposed.     

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.     

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.     

Second and third interaction virial coefficients of the (methane+propane) system determined from the speed of sound

The speed of sound has been measured in the binary gaseous mixture (0.85CH₄+0.15C₃H₈) along seven isotherms at temperatures between 225 and 375 K and at pressures up to 1.4 M Pa. From the measurements, second and third acoustic virial coefficients of the mixture were obtained. These results were analyzed together with values of the second and third acoustic virial coefficients of the two pure components to obtain a set of model intermolecular potential-energy functions for the methane-propane system. Nonpairwise additivity of the intermolecular forces was included in this analysis. Ordinary second and third interaction virial coefficients calculated from the model are reported, as are the second and third virial coefficients of the pure components. Gas densities calculated by means of these virial coefficients for the mixture (0.9298CH₄+0.0702C₃H₈) were found to agree with experimental values at temperatures between 280 and 330 K to within 0.02% at pressures up to 3 MPa and to within 0.08% at 4MPa.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Predicting the virial coefficients and thermodynamic properties of a multicomponent mixture with application to the ternary mixture of CH2F2+CF3CHF2+CF3CH2F

A model for estimating second and third virial coefficients, which has been used successfully to represent the behavior of pure gases and binary mixtures, was applied to a ternary mixture. An estimate for the ternary third virial coefficient.C ₁₂₃, was added to the model. Three experimentally determined binary interaction parameters were also used. The model has been applied to the ternary mixture CH₂F₂+CF₃CHF₂+CF₃CH₂F (R32+R125+R134a). The results are useful for calculating gas-phase densities, thermodynamic properties, and fugacities for phase equilibrium calculations. The use of such models leads to a considerable economy of effort in the case of multicomponent mixtures. Examples of the thermodynamic properties are given for the equimolar ternary mixture in the range from the dew-point temperature to 400 K at pressures of 0.5, 1, and 2 MPa. Calculated densities and speeds of sound are compared with new experimental values for a near-equimolar composition.     

Gaseous thermal conductivity of difluoromethane (HFC-32), pentafluoroethane (HFC-125), and their mixtures

The gaseous thermal conductivity of dilluoromethane (HFC-32). pentalluoroethane (HFC-125). and their binary mixtures was measured with a transient hot-wire apparatus in the temperature ranges 283–333 K at pressures up to saturation. The uncertainty of the data is estimated to be within I %. The thermal conductivity as a function of composition of the mixtures at constant pressure and temperature is found to have a small maximum near 0.3–0.4 mole fraction of HFC-32. The gaseous thermal-conductivity data obtained for pure HFC-32 and HFC-125 were correlated with temperature and density together with the liquid thermal-conductivity data from the literature, based on the excess thermal-conductivity concept. The composition dependence of the thermal conductivity at a constant temperature is represented with the aid of the Wassiljewa equation.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado. U.S.A.     

HFC-227ea的气相pvT性质

改进了实验室原有的pvT实验台,测量了HFC-227ea气相pvT性质。膨胀法和等容法相结合,仅需一次充注,沿10条定容线测量了共80组实验数据。实验数据的温度范围为310-410K,压力最大到3．2MPa。首先对超临界410K等温线的数据进行了膨胀法分析,建立了压力和密度关系。以此为基础,获得了各条定容线的密度。建立了HFC-227ea的气相状态方程,与已发表的HFC-227ea的pvT数据进行了比较,实验数据的最大压力偏差小于0．07％,与其他人实验数据也符合良好。状态方程还能精确计算气相声速,与实验数据的最大偏差小于0．05％,说明数据和状态方程都是准确可靠的。     

Survey of Experimental Data of Thermophysical Properties for Difluoromethane (HFC-32)

A survey of experimental data for HFC-32 was prepared at the Institute of Thermomechanics in connection with planned experiments. In tabular form, surveys of thermodynamic, transport, and other property measurements, including pvT behavior, second virial coefficient, vapor pressure, saturation densities, critical parameters, heat capacities, speed of sound, thermal conductivity, viscosity, surface tension, refractive index, dielectric constant, and dipole moment, are presented. Tables include author)s) name(s), reference, year of publication, ranges of measurements, number of points, stated uncertainty, sample purity, and experimental method.     

Effective Intermolecular Interaction Potentials of Gaseous Fluorine,Chlorine, Bromine,and Iodine

Results are presented for binary intermolecular interactions and thermophysical properties in the temperature range between 70K and 1,000K of gaseous fluorine (F₂), and between 200K and 1,000K of chlorine (Cl₂), bromine (Br₂), and iodine (I₂). Our studies are carried out with an (n − 6) Lennard-Jones temperature-dependent potential (LJTDP). The underlying model takes into account the influence of vibrational excitations on the equilibrium distance R _m(T) and potential well depth e(T){\varepsilon(T)} . The potential parameters at T = 0K have been obtained by minimization of the sum of squared deviations between experimentally determined and calculated second pVT- and acoustic virial coefficients, B and β, and viscosities η, normalized to their relative experimental error a _exp. The majority of the available experimental data are well reproduced within their experimental errors. Tables and fitting formulae for a fast and reliable prediction of the thermophysical properties and potential parameters are also presented.     

Viscosity of Gaseous Mixtures of HFC-125 + Propane from 298.15 to 423.15 K at Pressures to 6.7 MPa

This paper reports experimental results for the viscosity of gaseous mixtures of HFC-125 (pentafluoroethane) + propane. The measurements were carried out with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K. The viscosity was measured for two mixtures containing 50.11 and 75.03 mol% HFC-125 in propane. The viscosity at normal pressure was analyzed with the extended law of corresponding states developed by Kestin et al., and the scaling parameters were obtained for unlike-pair interactions between HFC-125 and propane. The modified Enskog theory developed by Vesovic and Wakeham was applied to predict the viscosity for the binary gaseous mixtures under pressure. From comparisons between experimental results and calculated values of the HFC-125 + propane system, it should be concluded that the Vesovic-Wakeham method gives reliable predictions for the viscosity of a gaseous mixture containing both polar and nonpolar compounds.