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.     

Measurements of Gaseous PVTx Properties and Saturated Vapor Densities of Refrigerant Mixture R-125+R-143a

The experimental PVTx properties of a binary refrigerant mixture, R-125 (pentafluoroethane)+R-143a (1,1,1-trifluoroethane), have been measured for a composition of 50 mass% R-125 by a constant-mass method coupled with an expansion procedure in a range of temperatures from 305 to 400 K, pressures from 1.5 to 6.1 MPa, and densities from 92 to 300 kg·m^–3. The experimental uncertainties of the present measurements are estimated to be within ±7.2 mK in temperature, ±3.0 kPa in pressure, ±0.12 kg·m^–3 in density, and ±0.040 mass% in composition. The sample purities are 99.953 mass% for R-125 and 99.998% for R-143a. Seven saturated vapor densities and dew point pressures of the R-125+R-143a system were determined, on the basis of rather detailed PVTx properties measured in the vicinity of the saturation boundary as well as the thermodynamic behavior of isochores near saturation. The second and third virial coefficients for temperatures from 330 to 400 K were also determined.     

Saturated liquid densities and bubble-point pressures of the binary HFC 152a+HCFC 142b system

Forty-eight sets of the saturated liquid densities and bubble-point pressures of the binary HFC 152a + HCFC 142b system were measured with a magnetic densimeter coupled with a variable-volume cell. The measurements obtained at four compositions, 20, 40, 60, and 80 wt%, of HFC 152a cover a range of temperatures from 280 to 400 K. The experimental uncertainties in temperature, pressure, density, and composition were estimated to be within ±15mK, ±20kPa, ±0.2%, and between –0.14 and ±0.01 wt% HFC 152a (–0.01 and + 0.14 wt% HCFC 142b), respectively. The purities of the samples were 99.9 wt% for HFC 152a and 99.8 wt% for HCFC 142b. A binary interaction parameter, k _ij , in the Peng-Robinson equation of state was determined as a function of temperature for representing the bubble-point pressures. On the other hand, two constant binary-interaction parameters, k _ij and l _ij , were introduced into the mixing rule of the Hankinson-Brobst-Thomson equation for representing the saturated liquid densities.     

Bubble pressures and saturated liquid densities of R 22 + R 114 mixtures in the range 310–400 K

The bubble pressures and saturated liquid densities of mixtures of R 22 and R 114 have been measured with a static and synthetic method with a variable-volume cell. The results for five different compositions (100, 75, 50, 25, and 0 mol% R 22) cover the temperature range from 310 to 400 K. The experimental data for both pure components are compared with literature data, showing the reliability of the present results. The system shows positive deviations from Raoult's law at temperatures below 340 K and the deviations increase with decreasing temperature. The 25 mol % R 22 mixture shows the maximum non-ideality.     

Measurements of Saturation Densities in Critical Region and Critical Loci for Binary R-32/125 and R-125/143a Systems

R-32/125 (difluoromethane/pentafluoroethane) and R-125/143a (pentafluoro-ethane/l,l,l-trifluoroethane) binary systems are promising alternative refrigerants to replace conventional refrigerants, i.e., R-22 and R-502. The saturated vapor- and liquid-density data in the critical region of these mixtures were measured using the visual observation of the meniscus disappearance in an optical cell. For the R-32/125 system, 35 saturation density data were measured at three compositions, 10, 35, and 50 mass% R-32. Nineteen saturation density data were also measured for R-125/143a (50/50 mass%). The critical temperatures and densities for these binary refrigerants were determined by taking into consideration the level and location of the meniscus disappearance as well as the intensity of the critical opalescence. Correlations to represent the critical loci of these binary refrigerants for an entire range of compositions have been developed. The experimental uncertainties of the saturation density data are estimated to be within 9 mK in temperature and 0.5 to 5.0 kg · m^–3 in density. The uncertainties of the critical temperature and density are estimated to be within 12 to 14mK and 4 to 8kg · m^–3, respectively.     

Dew- and bubble-point measurements for the mixtures of dichlorodifluoromethane and bromotrifluoromethane

The dew and bubble points for the mixtures of dichlorodifluoromethane (CCl₂F₂; R 12) and bromotrifluoromethane (CBrF₃; R13B1) were measured with the use of a constant-volume method coupled with an expansion procedure and visual observation of the meniscus at the vapor-liquid interface. In order to check the reliability of the apparatus used, vapor pressure measurements were conducted for carbon dioxide at 273.15 K and for two pure components, CCl₂F₂ and CBrF₃. Thirty-eight dew and bubble points of the CCl₂F₂+CBrF₃ system were determined for four different compositions of 0, 21, 45, and 70 mol % CBrF₃ in the range of temperatures from 299 to 384 K, pressures up to 4.2 MPa, and densities from 89 to 1228 kg · m^–1.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Phase behavior of the system He-N2 at high pressures

Recent investigation at our institute revealed that the solid-fluid-fluid three-phase line of the system helium-nitrogen shows two quadruple points in the pressure range up to 10 GPa. Since each quadruple point is connected with four three-phase lines, the phase diagram is very complicated. We have detected the phase transitions representing solid-solid-fluid equilibria. Moreover, two lines of constant composition have been determined as a function of temperature and pressure. These results are discussed together with the implications for the phase diagram of both He-N₂ and pure nitrogen.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Determination of binary mixture vapor-liquid critical densities from coexisting density data

Two-phase vapor-liquid equilibrium (VLE) isochores for binary mixtures are defined as the thermodynamic paths along which the overall density and composition are fixed. Data along such isochores are generated from a modified Leung-Griffiths model fit to experimental data for the binary system nitrogen-methane. The behavior of the liquid volume fraction along these isochores is found to be similar to that for pure fluids. Rectilinear diameters for varying overall densities (fixed composition) are seen to be nearly coincident. Straight-line diameters and the critical liquid volume fraction method are utilized to predict critical densities using data near and removed from the critical point. Both methods give acceptable results but the critical liquid volume fraction method is more accurate. A critical literature review of the need for binary mixture critical densities is presented and a proposed experimental procedure is given for the determination of mixture critical densities.     

Vapor–Liquid Equilibria For The Binary Difluoromethane (R-32) + Propane (R-290) Mixture

The vapor–liquid equilibrium of the mixture composed of difluoromethane (R-32) and propane (R-290) was studied in the temperature range between 273.15 and 313.15 K. The experimental uncertainties of temperature, pressure, and composition measurements were estimated to be within ±10 mK, ±3 kPa, and ±0.4mol%, respectively. Comparisons between the present data and available experimental data were made using the Helmholtz free energy mixture model (HMM) adopted in the thermophysical properties program package, REFPROP 6.0, as a baseline. In addition, the existence of an azeotrope and the determination of new adjustable parameters for HMM for the R-32 + R-290 mixture are discussed.     

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%.     

Phase behavior of mixtures at very high pressures

The invention of the diamond anvil cell (DAC) has been an enormous stimulus to high-pressure research. This technique has only recently been used to investigate the behavior of binary systems, probably because of the extra experimental problems which arise in the study of mixtures. It will be shown that a variety of aspects of the behavior of the mixture can, nevertheless, be studied under extreme conditions. Although the first investigations were carried out only recently, some very interesting results have already been obtained. A variety of two-components systems has been studied, e.g., He-Kr, Ne-Xe, He-H₂, NH₃-H₂O, and N₂-He₂. Some of these results are discussed. Finally, a comparison is made between experimental results and theoretical calculations.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Vapor-liquid equilibria for the ternary system N2 + CO2 +n-C4H10 at 250 and 270 K1

The system studied was nitrogen + carbon dioxide +n-butane at 250 and 270 K and at pressures from 1.5 to 14 MPa. The Peng-Robinson equation was used to model the results, since it is the most widely accepted equation of state in the gas processing industry. In general, the predictions are most accurate at low and moderate pressures and poorest at high pressures, especially near the critical region.     

Bubble pressures and saturated liquid molar volumes of difluoromonochloromethane—fluorochloroethane binary mixtures: experimental data and modelling

A previously described apparatus (variable volume cell method) was used to obtain bubble pressures and saturated liquid molar volumes at four temperatures for systems involving difluoromonochloromethane with tetrafluorodichloroethane, trifluorotrichloroethane and difluoromonochloroethane. The experimental bubble pressures are well represented by the Peng-Robinson equation of state with one adjusted interaction parameter. Adjusting a second interaction parameter does not significantly improve the representation. Soave and Mathias equations give a quite similar representation. Saturated liquid molar volumes calculated from the different equations of state, with binary interaction parameters adjusted on bubble pressure data, do not agree well with experimental results: the standard deviation between calculated and experimental densities is ≈ 8% with the Peng-Robinson equation of state and ≈ 18% with that of Soave and Mathias.     

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric densities of tetramethylsilane and 2,2-dimethylpropane have been measured by means of a hydrostatic density balance. For tetramethylsilane the liquid density has been determined from 289.73 K to the critical point 448.60 K and the vapor density from 353.55 K to the critical point, while for 2,2-dimethylpropane the liquid density has been measured from 290.88 K to the critical point 433.71 K and the vapor density from 349.01 K to the critical point. The results are represented well by the extended-scaling equation of Wegner with three correction terms and the critical indices α,β, andΔ ₁, obtained from renormalization-group theory. The fit is not improved by a term expressing an anomaly in the diameter using either of the exponents (1−α) or 2β. The critical density for tetramethylsilane is estimated as (0.2436±0.0001) g·cm⁻³ and that for 2,2-dimethylpropane as (0.2318±0.0001) g·cm⁻³.     

Thermal conductivity of organic liquid binary mixtures: Measurements and prediction method

A correlation presented in previous papers for the prediction of organic liquid thermal conductivity, , is generalized in order to estimate the thermal conductivity of the binary mixtures of organic liquids. The proposed equation contains the reduced temperature, the molar fractions, and two factors characteristic of the components. The comparison between predicted and experimental A values is developed at atmospheric pressure, taking into account data present in the literature and experimental values obtained at the Department of Energy of Ancona University, using the steady-state hot-wire method. Fifty binary mixtures are considered (28 of them are investigated by the authors at 25 and 50°C), and the mean general deviation between predicted and experimental thermal conductivity values (621 data points) is 2.5%.     

Thermodynamic property representation for the R-32/125 binary system by a new cubic equation of state

Thermodynamic properties of the R-32/125 binary system are modeled by a new cubic equation of state which was developed and applied to the pure R-32 and R-125 in a previous paper by the present authors. The essential thermodynamic properties such as PVTx properties, vapor-liquid equilibrium, enthalpy, entropy, isobaric specific heat, and speed of sound are well represented by the new model simultaneously for the liquid phase, the gas phase, and the two-phase region of the R-32/125 binary system. The developed model is valid for the entire range of compositions, and a pressure-enthalpy diagram for a R-32/125 mixture with 50 mass% of R-32 is illustrated as an example. The new model was also compared with other reported models in refrigeration cycle calculations.     

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 equilibrium of near-critical binary alkane mixtures

The modified Leung-Griffiths model of Rainwater and Moldover is used to correlate vapor-liquid equilibrium (VLE) surfaces in pressure, temperature, and density for binary mixtures in the near-critical region. The systems studied are butane-pentane, propane-isopentane, butane-hexane, and ethane-butane. The model, which has also successfully fit several other mixtures, is based on scaling-law equations of state expressed in terms of field variables. It incorporates a variation of the principle of corresponding states as well as the coupling of density and composition change across the phase boundary. As the width of the dew-bubble curves increases, additional parameters are required to obtain successful VLE correlations.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.