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.     

Liquid Thermal Conductivity of Binary Mixtures of Pentafluoroethane (R125) and 1,1,1,2-Tetrafluoroethane (R134a)

Thermal conductivities of zeotropic mixtures of R125 (CF₃CHF₂) and R134a (CF₃CH₂F) in the liquid phase are reported. Thermal conductivities have been measured by a transient hot-wire method with one bare platinum wire. Measurements have been carried out in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa. The dependence of thermal conductivity on temperature, pressure, and composition of the binary mixture is presented. Measured thermal conductivity data are correlated as a function of temperature, pressure, and overall composition of the mixture. The uncertainty of our measurements was estimated to be better than 2%.     

Viscosity of Gaseous HFC-134a (1,1,1,2-Tetrafluoroethane) Under High Pressures

The viscosity of gaseous HFC-134a (1,1,1,2-tetrafluoroethane) was measured with an oscillating disk viscometer of the Maxwell type from 298.15 to 398.15 K at pressures up to 5.5 MPa. Intermolecular potential parameters for the Lennard–Jones 12-6 model were determined from the viscosity data at 0.1 MPa. The viscosity equation developed by Krauss et al. was applied to correlate the present viscosity data. In addition, the correlations proposed by Stiel and Thodos and by Lee and Thodos were tested for fitting the experimental viscosity data.     

Equations for the Thermal Conductivity of R-32, R-125, R-134a,and R-143a

At present hydrofluorocarbons (HFCs) such as R32, R-125, R-134a, and R-143a are widely used, and it is required to obtain accurate information of thermophysical properties, especially of the thermal conductivity of HFCs. In this paper new thermal conductivity equations for R-32, R-125, R134a, and R143a are proposed, applicable over a wide range of temperature and pressure including the critical region based on existing experimental data, and the reliability of the present equations is summarized. The problem that the thermal conductivity calculated from the thermal diffusivity in the critical region differs depending on the equation of state is also discussed. Paper presented at the Sixteenth European Conference for Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

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%.     

Transport Property Measurements on the IUPAC Sample of 1,1,1,2-Tetrafluoroethane (R134a)

This paper reports the results of an international project coordinated by the Subcommittee on Transport Properties of Commission I.2 of the International Union of Pure and Applied Chemistry. The project has been conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of R134a and culminates the effort which was initially described in 1995. The project has involved the remeasurement of the transport properties of a single sample of R134a in nine laboratories throughout the world in order to test the hypothesis that at least part of the discrepancy could be attributed to the purity of the samples. This paper provides an intercomparison of the new experimental results obtained for the viscosity and thermal conductivity in the vapor, liquid, and supercritical gas phases. The viscosity measurements were made with a variety of techniques including the vibrating wire, oscillating disk, capillary flow, and falling body. Thermal conductivity was measured using transient bare and anodized hot wires, steady-state anodized hot wires, and light scattering. Agreement between a variety of experimental techniques using the standard round-robin sample is necessary to demonstrate that some of the discrepancies in earlier results were due to sample impurities. Identification of disagreement between data using one experimental technique relative to other techniques may suggest modifications that would lead to more accurate measurements on these highly polar refrigerant materials. It is anticipated that the new data which have been measured on this IUPAC round-robin sample will aid in the identification of the reliable data sets in the literature and ultimately allow the refinement of the IUPAC reference-data correlations for the transport properties of R134a.     

Thermophysical properties of 1,1,1,2-tetrafluoroethane (R-134a)

The present hypothesis of depletion of the stratospheric ozone layer by some chlorofluorocarbons has prompted a lot of research and development of new stratospherically safe fluids in various uses such as refrigerants, blowing agents in foams, aerosol propellants, solvents, and many other uses. In the areas of certain refrigeration needs 1,1,1,2-tetrafluoroethane (R-134a) has been considered as a possible alternate to the use of dichloro-difluoromethane (R-12), the most commonly used refrigerant. R-12 is estimated to have a higher potential for ozone depletion. This will require a large number of thermophysical property data to help in designing equipment and also in manufacturing R-134a. This paper is intended to fill that need. The paper details the measurement and correlation of some of the important thermophysical properties such as vapor pressure, liquid density, and pressure-volume-temperature. The measured P-V-T data have been used to generate a Martin-Hou-type equation of state for this fluid over a wide range of temperature and pressure. Correlating equations are also developed for vapor pressure, liquid density, and ideal-gas specific heat. Ideal-gas specific heat has been estimated from measured spectroscopic data. The correlating equations can be used to generate the thermodynamic tables and charts. The critical temperature of R-134a has also been measured. Critical density and pressure have been estimated from measured data. The data and the correlations presented here are expected to be very useful to the refrigeration industry in the development of R-134a as a working fluid for refrigeration applications.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The thermal conductivity of liquid 1,1,1,2-tetrafluoroethane (HFC 134a)

The thermal conductivity of HFC 134a was measured in the liquid phase with the polarized transient hot-wire technique. The experiments were performed at temperatures from 213 to 293 K at pressures up to 20 MPa. The data were analyzed to obtain correlations in terms of density and pressure. This study is part of an international project coordinated by the Subcommittee on Transport Properties of Commission 1.2 of IUPAC, conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of HFC 134a, using samples of different origin. Two samples of HFC 134a from different sources have been used. The thermal conductivity of the first sample was measured along the saturation line as a function of temperature and the data were presented earlier. The thermal conductivity of the second one, the round-robin sample was measured as a function of pressure and temperature. These data were extrapolated to the saturation line and compared with the data obtained, previously in order to demonstrate the importance of the sample origin and their real purity. The accuracy of the measurements is estimated to be 0.5%. Finally, the results are compared with the existing literature data.     

The vapor pressure of 1,1,1,2-tetrafluoroethane (R134a) and chlorodifluoromethane (R22)

We measured the vapor pressure of chlorodifluoromethane (commonly known as R22) at temperatures between 217.1 and 248.5 K and of 1,1,1,2-tetrafluoroethane (commonly known as R134a) in the temperature range 214.4 to 264.7 K using a comparative ebulliometer. For 1,1,1,2-tetrafluoroethane at pressures between 220.8 and 1017.7kPa (corresponding to temperatures in the range 265.6 to 313.2K), additional measurements were made with a Burnett apparatus. We have combined our results for 1,1,1,2-tetrafluoroethane with those already published from this laboratory at higher pressures to obtain a smoothing equation for the vapor pressure from 215 K to the critical temperature. For chlorodifluoromethane our results have been combined with certain published results to provide an equation for the vapor pressure at temperatures from 217 K to the critical temperature.     

Transport properties of 1,1,1,2-tetrafluoroethane (R134a)

New equations for the thermal conductivity and the viscosity of R134a that are valid in a wide range of pressures and temperatures are presented. They were obtained through a theoretically based, critical evaluation of the available experimental data, which showed considerable inconsistencies between data sets, in particular in the vapor phase. In the critical region the observed enhancement in the thermal conductivity is well represented by a crossover model for the transport properties of fluids. Since thermodynamic properties enter into the calculation of the critical enhancement of the transport properties, a new fundamental equation for the critical region was developed also.Paper dedicated to Professor Joseph Kestin.     

Liquid Thermal Conductivity of Ternary Mixtures of Difluoromethane (R32), Pentafluoroethane (R125), and 1,1,1,2-Tetrafluoroethane (R134a)1

The thermal conductivities of ternary refrigerant mixtures of difluoromethane (R32), pentafluoroethane (R125), and 1,1,1,2-tetrafluoroethane (R134a) in the liquid phase have been measured by the transient hot-wire method with one bare platinum wire. The experiments were performed in the temperature range of 233 to 323 K and in the pressure range of 2 to 20 MPa at various compositions. The measured data are correlated as a function of temperature, pressure, and composition. From the correlation, we can calculate the thermal conductivity of pure refrigerants and their binary or ternary refrigerant mixtures. The uncertainty of the measurements is estimated to be ±2%.     

Thermal stability of R-134a, R-141b, R-13I1, R-7146, R-125 associated with stainless steel as a containing material

An experimental apparatus for assessing the thermal stability threshold of refrigerant working fluids is described and results for R-134a (1,1,1,2-tetrafluoroethane), R141b (1,1-dichloro-1-fluoroethane), R-13I1 (trifluoromethyl iodide), R-7146 (sulphur hexafluoride), R-125 (pentafluoroethane) are presented. The information is a concern for the design of refrigeration systems, high temperature heat pumps and Organic Rankine Cycles (ORC), for which the above refrigerants are proposed. The method aims to identify a maximum temperature for plant operation in contact with stainless steel and involves the evaluation of four indicators: (1) pressure variation while the fluid is maintained at set temperature; (2) saturation pressure comparison after heat treatment; (3) chemical analysis; and (4) vessel visual inspection after the test session. The highest temperatures at which no evident degradation occured are: 368°C for R-134a; 102°C for R-13I1; 90°C for R-141b; 204°C for R-7146; and 396°C for R-125.     

Vapour pressure measurements on 1,1,1,2-tetrafluoroethane (R134a) from 180 to 350 K

Measurements of vapour pressures were made for 1,1,1,2-tetrafluoroethane (R134a) from 180 to 350 K by using a static cell. Temperatures were measured with a platinum resistance thermometer to within an accuracy of ±0.03 K. Pressures were measured with calibrated oscillating quartz-crystal pressure transducers with uncertainties estimated to range from 0.02 to 1.8 kPa.     

Bubble-Point Pressures and Saturated- and Compressed-Liquid Densities of the Binary R-125 + R-143a System

Bubble-point pressures and saturated- and compressed-liquid densities of the binary R-125 (pentafluoroethane) + R-143a (1,1,1 -trifluoroethane) system have been measured for several compositions at temperatures from 280 to 330 K by means of a magnetic densimeter coupled with a variable-volume cell mounted with a metallic bellows. The experimental uncertainties of the temperature, pressure, density, and composition were estimated to be within ±10mK, ± 12 kPa, ±0.2%, and ±0.2mass%, respectively. The purities of the samples used throughout the measurements are 99.96 area% for R-125 and 99.94 area% for R-143a. Based on these measurements, the thermodynamic behavior of the vapor-liquid equilibria of this binary refrigerant mixture has been represented using the Peng–Robinson equation for the bubble-point pressures, a correlation for the saturated-liquid densities, and an equation of state for the compressed-liquid densities.     

Thermodynamic properties of 1,1,1,2-tetrafluoroethane (R134a) in the critical region

A theoretically based simplified crossover model, which is capable of representing the thermodynamic properties of fluids in a large range of temperatures and densities around the critical point, is presented. The model is used to predict the thermodynamic properties of R134a in the critical region from a limited amount of available experimental information. Values for various thermodynamic properties of R134a at densities from 2 to 8 mol·L^–1 and at temperatures from 365 to 450 K are presented.     

Sound velocity and ideal-gas specific heat of gaseous 1,1,1,2-tetrafluoroethane (R134a)

A cylindrical, variable-path acoustic interferometer operating at 156.252kHz is developed for determining ideal-gas specific heats. Results of validation measurements with argon are very satisfactory, with the maximum deviation of the speed of sound equal to 3×10^–4. The sound velocity of gaseous R134a has been measured at low temperatures and low pressures. The specific heat was then calculated from the results. The experimental results corrected for various dispersions for the sound velocity of gaseous R134a match well with an earlier publication, with a room mean square deviation of 2.56×10^–4. A new relation for the ideal-gas specific heat as a function of temperature for R134a is obtained.     

Boiling heat transfer of R-22, R-134a, and CO2 in horizontal smooth minichannels

This study examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO₂. The local heat transfer coefficients were obtained for heat fluxes ranging from 10 to 40 kW m⁻², mass fluxes ranging from 200 to 600 kg m⁻² s⁻¹, a saturation temperature of 10 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 2000 mm. The section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. An increasing and decreasing heat transfer coefficient occurred at the lower vapor quality with increasing heat flux and mass flux. The mean heat transfer coefficient ratio of R-22:R-134a:CO₂ was approximately 1.0:0.8:2.0. Laminar flow was observed in the minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in minichannels was developed with a mean deviation of 11.21%.     

An equation of state formulation of the thermodynamic properties of R134a (1,1,1,2-tetrafluoroethane)

New correlations for the thermodynamics properties of R134a are presented. A classical equation for the molar Helmholtz energy is used with temperature and density as the independent variables. The equation is accurate for both the liquid and vapour phases at pressures up to 70 Pa, and for a temperature range from the triple point to 450 K. Temperatures are given on the new International Temperature Scale of 1990 (ITS 90). The equation was developed by using experimental data for pressure-volume-temperature (PVT) properties, isochoric heat capacity, second virial coefficients, speed of sound and coexistence properties. Comparisons with experimental data and with two other equations of state are given. Ancillary equations representing the saturated liquid and vapour densities and the vapour pressure are also presented.     

Liquid viscosities and densities of HFC-134a+glycol mixtures

Liquid viscosity and density of six binary mixtures of HFC-134a with glycols [ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (400), and polypropylene glycol (2000)] have been measured in the temperature range from 273 to 333 K. The viscosity was measured by a rolling-ball viscometer calibrated with standard liquids of viscosities and densities (JS5, JS10, JS20, and JS50). The density was measured with a glass pycnometer. The uncertainties of the measurements were estimated to be less than 3.4 % for viscosity and 0.04 % for density, respectively. An equation is given to represent the obtained viscosity values as a function of weight fraction and temperature.     

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.