A Multiparameter Thermal Conductivity Equation for 1,1-Difluoroethane (R152a) with an Optimized Functional Form

The application of an optimization technique to the available experimental data has led to the development of a new multiparameter equation λ = λ (T,ρ ) for the representation of the thermal conductivity of 1,1-difluoroethane (R152a). The region of validity of the proposed equation covers the temperature range from 220 to 460 K and pressures up to 55 MPa, including the near-critical region. The average absolute deviation of the equation with respect to the selected 939 primary data points is 1.32%. The proposed equation represents therefore a significant improvement with respect to the literature conventional equation. The density value required by the equation is calculated at the chosen temperature and pressure conditions using a high accuracy equation of state for the fluid.Paper presented at the Seventeenth European Conference on Thermophysical Properties,September 5–8, 2005, Bratislava, Slovak Republic.     

Saturated Liquid Viscosity and Surface Tension of Alternative Refrigerants

Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, we carried out the simultaneous determination of the surface tension and the liquid kinematic viscosity of some alternative refrigerants by surface light scattering (SLS) on a gas–liquid interface. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). R23 (trifluoromethane), R32 (difluoromethane), R125 (pentafluoroethane), R143a (1,1,1-trifluoroethane), R134a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), and R123 (2,2-dichloro-1,1,1-trifluoroethane) were investigated under saturation conditions over a wide temperature range, from 233 K up to the critical point. It is estimated that the uncertainty of the present surface tension data for the whole temperature range is less than ±0.2 mN·m^–1. For temperatures up to about 0.95T _c, the kinematic viscosity of the liquid phase could be obtained with an absolute accuracy of better than 2%. For the highest temperatures studied in this work, measurements for the kinematic viscosity exhibit a maximum uncertainty of about ±4%. Viscosity and surface tension data are represented by a polynomial function of temperature and by a van der Waals-type surface tension equation, respectively. The results are discussed in detail with comparison to literature data.     

A fundamental equation of state for 1,1-difluoroethane (HFC-152a)

A fundamental equation ofstale for HFC-152a ( 1,1-dilluorocthane) is presented covering temperatures between the triple-point temperature ( 154.56 K) and 435 K for pressures up to 311 M Pa. The equation is based on reliable (p, g, T) data in the range mentioned above. These are generally represented within ±0.1 % of density. Furthermore. experimental values of the vapor pressure, the saturated liquid density, and some isobaric heat capacities in the liquid were included during the correlation process. The new equation of state is compared with experimental data and also with the equation of state developed by Tamatsu et al. Differences between the two equations of state generally result from using different experimental input data. It is shown that the new equation of state allows an accurate calculation of various thermodynamic properties for most technical applications.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder. Colorado. U.S.A.     

An equation of state for 1,1-difluroethane (HFC 152a)

An equation of state for 1,1-difluoroethane (HFC 152a, CH₃CHF₂) has been developed on the basis of reliable experimental data including PVT, liquid C_p, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m⁻³. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a.     

The thermal conductivity of R22, R142b,R152a,and their mixtures in the liquid state

An experimental apparatus for measuring the thermal conductivity of liquids by the transient hot-wire method was constructed and tested with toluene as a standard liquid. Measurements were performed on R22, R142b, and R152a. The thermal conductivities of mixtures of R142b and R152a with R22 were also measured by varying the weight fraction of R22. Experiments were performed in the range from –50 to 50°C and from 2 to 20 MPa and the measured data are analyzed to obtain a correlation in terms of temperature, pressure, and composition of the mixture. While the thermal conductivity of R22 + R152a mixtures varies monotonously with composition, that of R22 + R142b mixtures turned out to go through an extremum value. The accuracy of our measurements is estimated to be within 2%.Paper dedicated to Professor Joseph Kestin.     

A Multiparameter Viscosity Equation for 1,1-Difluoroethane (R152a) with an Optimized Functional Form

This paper presents a new formulation for the viscosity surface of 1,1-difluoroethane (R152a). The formulation is a multiparameter equation η = η(ρ, T) obtained from an optimization technique of the functional form based on available experimental data. The equation is valid for temperatures from 240 to 440 K and pressures up to 20 MPa. Two lines of viscosity minima have been observed, and they have been analytically defined. A high accuracy equation of state for R152a was used to convert the experimental variables (P,T) into the independent variables of the viscosity equation (ρ, T). Comparisons with data are given to establish the accuracy of the viscosity values calculated using this equation. The obtained results are very satisfactory with an average absolute deviation of 0.27% for the selected 264 primary data points, and this is a significant improvement with respect to other equations in the literature.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5-8, 2005, Bratislava, Slovak Republic.     

Thermal diffusivity of the alternative refrigerant R152a

The thermal diffusivity of R152a was measured by dynamic light scattering. We have developed an apparatus which enables us to apply both homodyne and heterodyne light-scattering techniques allowing a wide region of state to be investigated. A total of 300 data points was obtained along the critical isochore. in both coexisting phases and on seven isotherms with densities and temperatures ranging from 50 to 1000 kg·m⁻³ and 290 to 425 K, respectively. The uncertainty of the measurements lies between 0.5 and 5%. The thermal-diffusivity values cover a range of over four orders of magnitude and include the region around the vapor-liquid critical point. Other measured properties are temperature, pressure, and refractive index as well as the critical parametersT _c andp _c .     

Measurements of the viscosity of refrigerants in the vapor phase

Measurements of the viscosity of refrigerants R124, R125, R134a, and R152a in the vapor phase are presented. The measurements, performed in a new vibrating-wire instrument, cover a temperature range from 273 to 333 K from about atmospheric pressure up to below the saturation pressure. The uncertainty of the reported values is estimated to be better than ±1%. Comparison with measurements of other investigators reveals a lack of reliable data in the vapor region for these compounds. Paper presented at the Fourth Asian Thermophysical Properties Conference., September 5–8, 1995, Tokyo, Japan.     

Performance of ejector cooling systems using low ecological impact refrigerants

The theoretical behaviour of an ejector cooling system, using as working fluids propane, butane, isobutane, R152a and R134a, is obtained. The ejector works as a thermo-compressor that is simulated with a validated one-dimensional mathematical model, whose errors are lower than 6%. For a system unitary cooling capacity, a parametric study is carried out varying the generation, condensation and evaporation temperatures. From the obtained data, a complete analysis of the system performance can be achieved when the ejector and system operation parameters are considered. The best performance corresponds to the system using propane, because has the highest system coefficient of performance and its ejector has the maximum entrainment ratio value, the least area ratio value and the highest efficiency value. The considered generation temperature ranging from 70 °C to 95 °C is appropriate for low-grade energy sources assisting thermal cooling systems. After this system performance, come those in which R152a and R134a are employed, with isobutane and butane at the end. The obtained results represent potential design points of an efficient ejector cooling system operation, because to each combination of the above mentioned temperatures corresponds one and only one ejector geometry.     

An experimental study of the thermodynamic properties of 1,1-difluoroethane

Experimental vapor pressures andP--T data of an important alternative refrigerant, 1, 1-difluoroethane (HFC-152a), have been measured by means of a constant-volume method coupled with expansion procedures. SixtyP--T data were measured along eight isochores in a range of temperaturesT from 330 to 440 K, at pressuresP from 1.6 to 9.3 MPa, and at densities from 51 to 811 kg·m^–3. Forty-six vapor pressures were also measured at temperatures from 320 K to the critical temperature. The uncertainties of the temperature and pressure measurements are within ±7mK and ±2kPa, respectively, while the uncertainty of the density values is within ±0.1%. The purity of the sample used is 99.9 wt%. On the basis of the measurements along each isochore, five saturation points were determined and the critical pressure was determined by correlating the vapor-pressure measurements. The second and third virial coefficients for temperatures from 360 to 440 K have also been determined.     

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.     

Ideal-Gas Heat Capacity Values and Equations for Hydrofluorocarbon (HFC) Refrigerants Based on Speed-of-Sound Measurements

Final values of ideal-gas heat capacity c ⁰ _p derived from speed-of-sound measurements using an acoustic spherical resonator and equations of c ⁰ _p as a simple function of temperature are provided from an overall assessment of speed-of-sound measurements for five hydrofluorocarbon (HFC) refrigerants, difluoromethane (R32), pentafluoroethane (R125), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a). Some of the experimental results had systematic errors in comparison with theoretical calculations based on spectroscopic data, which seem to result from the impurity of the sample fluids. The agreement of the experimentally determined and theoretically calculated c ⁰ _p values was confirmed for HFC refrigerants. The uncertainty of c ⁰ _p values calculated from the proposed equations is estimated to be 0.1 or 0.2% corresponding to an ISO uncertainty with a coverage factor of k=1. An erratum for Table I in a previous report by Yokozeki et al. in 1999 is provided as an appendix.     

Molar Heat Capacity at Constant Volume of 1,1-Difluoroethane (R152a) and 1,1,1-Trifluoroethane (R143a) from the Triple-Point Temperature to 345 K at Pressures to 35 MPa

Molar heat capacities at constant volume (C _v) of 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) have been measured with an adiabatic calorimeter. Temperatures ranged from their triple points to 345 K, and pressures up to 35 MPa. Measurements were conducted on the liquid in equilibrium with its vapor and on compressed liquid samples. The samples were of high purity, verified by chemical analysis of each fluid. For the samples, calorimetric results were obtained for two-phase ((C _v ⁽²⁾ ), saturated-liquid (C or C _x ^' ), and single-phase (C _v) molar heat capacities. The C data were used to estimate vapor pressures for values less than 105 kPa by applying a thermodynamic relationship between the saturated liquid heat capacity and the temperature derivatives of the vapor pressure. The triple-point temperature and the enthalpy of fusion were also measured for each substance. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) for C _v is estimated to be 0.7%, for C _v ⁽²⁾ it is 0.5%, and for C it is 0.7%.     

The viscosity of the refrigerant 1,1-difluoroethane along the saturation line

The viscosity coefficient of the refrigerant R152a (1,1-difluoroethane) has been measured along the saturation line both in the saturated liquid and in the saturated vapor. The data have been obtained every 10 K from 243 up to 393 K by means of a vibrating-wire viscometer using the free damped oscillation method. The density along the saturation line was calculated from the equation of state given by Tamatsu et al. with application of the saturated vapor-pressure correlation given by Higashi et al. An interesting result is that in the neighborhood of the critical point, the kinematic viscosity of the saturated liquid seems to coincide with that of the saturated vapor. The results for the saturated liquid are in satisfying agreement with those of Kumagai and Takahashi and of Phillips and Murphy. A comparison of the saturatedvaport data with the unsaturated-vapor data of Takahashi et al. shows some discrepancies.Paper dedicated to Professor Joseph Kestin.     

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%.     

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.     

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%.     

Transport properties of Freon-152a and Freon-142b in the temperature range of 280–510 K

The thermal conductivity of 1,1 difluoroethane (Freon-152a) and 1 chloro-1 difluoroethane (Freon-142b) are measured at several pressures in the range 29.7–75.8 kPa and as a function of temperature in the range 280–510 K. The thermal conductivity column instrument is employed, and the experimental values are estimated to be accurate within a maximum uncertainty of ±5.6% at the lowest temperature, which reduces to ±2.4% at the highest temperature. These conductivity values are compared with the predictions of Chapman-Enskog kinetic theory, with the correction factor for the internal energy transport estimated from Hirschfelder's theory, and the Lennard-Jones (12-6) potential. The experimental conductivity data are also utilized to generate the values for the two other transport properties in conjunction with the interrelations obtained between different properties on the basis of kinetic theory. The data on transport properties are employed to give the best possible estimates of Prandtl and Schmidt numbers as a function of temperature.     

Mixing rules for the specific heat capacities of several HFC-mixtures

The specific heat capacity at constant pressure (c_p) of some relevant HFCs as replacements for R12, R502 and R22 was measured. The liquids investigated are binary or ternary mixtures of R134a, R152a, R125, R32 and R143a. Empirical functional relations in polynomial forms between the temperature, specific heat capacity and concentration are established and the coefficients of the polynomial correlations are presented. These equations can be used to calculate the c_p-values for the mixtures investigated over the whole concentration range and the predicted properties generally agree with the source data to ca ± 0.1% for the pure substances. The accuracy of the measurements is better than <1% for the pure fluids and <1.5% for the mixtures. Differences between 1 and 2% can occur only at temperatures >40°C and < −50°C.     

Isochoric p-ρ-T Measurements on 1,1-Difluoroethane (R152a) from 158 to 400 K and 1,1,1-Trifluoroethane (R143a) from 166 to 400 K at Pressures to 35 MPa

The p--T relationships have been measured for 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 158 to 400 K for R152a and from 166 to 400 K for R143a, while pressures were up to 35 MPa. Measurements were conducted on compressed liquid samples. Determinations of saturated liquid densities were made by extrapolating each isochore to the vapor pressure, and determining the temperature and density at the intersection. Published p--T data are in good agreement with this study. For the p--T apparatus, the uncertainty of the temperature is ±0.03 K, and for pressure it is ±0.01% at p>3 MPa and ±0.05% at p&#60;3 MPa. The principal source of uncertainty is the cell volume (28.5 cm³), which has a standard uncertainty of ±0.003 cm³. When all components of experimental uncertainty are considered, the expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) of the density measurements is estimated to be ±0.05%.