Saturated-liquid densities and vapor pressures ofHFC-143a(l,l,l-trifluoroethane), , and HFC-125 (pentafluoroethane) were measured by a magnetic densimeter coupled with a metallic bellows in the range of temperatures from 220 to 340 K. The experimental uncertainties for temperature, pressure, and density measurements are estimated to be not greater than ±15 mK, ±10 kPa (for HFC-143a) or ±2 kPa (for HFC-32 and HFC-125), and ±0.2 %, respectively. The purities of HFC-143a, HFC-32, and HFC-125 used in the present measurements are 99.0 mol %, 99.998 mass %, and 99.8 mass %, respectively.

In the present paper, we report an experimental study on the liquid-phase thermodynamic properties of the new-generation alternative refrigerants, pentafluoroethyl methyl ether, CF 3 CF 2 OCH 3 (245cbEβγ), and heptafluoropropyl methyl ether, CF 3 CF 2 CF 2 OCH 3 (347sEγδ). The measurements of vapor pressures and saturated-and compressed-liquid densities were performed by means of a magnetic densimeter coupled with a variable-volume cell mounted with a metallic bellows for temperatures from 260 to 370 K (for CF 3 CF 2 OCH 3 ) and from 250 to 370 K (for CF 3 CF 2 CF 2 OCH 3 ) and pressures up to 3 MPa. The experimental uncertainties of the temperature, pressure, and density measurements were estimated to be within (8 mK, (1.9 kPa (single-phase measurements) and (2.5 kPa (two-phase vapor pressure measurements), and (2 kg‚m -3 , respectively. The purities of the samples used throughout the measurements were 99.99 mass % for CF 3 CF 2 CF 2 OCH 3 and 99.9 mass % for CF 3 CF 2 CF 2 OCH 3 . On the basis of these measurements and the available data reported by other investigators, the thermodynamic behaviors with respect to vapor pressures and saturated-and compressed-liquid densities are discussed in terms of vapor pressure and saturated liquid density correlations optimized and a liquid-phase equation of state. By examining the thermodynamic behavior of the derived properties such as the specific isochoric and isobaric heat capacities, speeds of sound, and Joule-Thomson coefficients, the range of validity for the optimized simple correlations and their physical soundness will be discussed.

The impurity effect on fixed-point temperature realization by thermal analysis has been assessed. For such an assessment, the following actions were conducted: (1) the fabrication of aluminium point cells using 6N or higher-grade aluminium samples from different sources (manufacturers), (2) temperature measurements during solidification and thermal analyses based on freezing curves obtained from the measurements, (3) direct cell comparison among cells of different nominal purities and (4) calculation of the departure of the freezing point from the ideally defined freezing point by applying the sum of individual estimates (SIE). Two aluminium point cells were prepared in action (1) using 6N-grade and one cell using 6N5-grade aluminium samples. To realize a fixed point using the cells, a fixed-point furnace was developed and evaluated. Temperature measurements in action (2) were conducted at different rates of solidification and in accordance with the one using the liquid–solid interface technique. Gradients of freezing curves were derived in the thermal analysis, and from their dependence on the rate of solidification, the impurity effect was evaluated. Indirect cell comparison was also derived using the difference in the gradients. It was found that the indirect cell comparison was in satisfactory agreement with the direct cell comparison, which was obtained from action (3). It was also found that the departure of the thermal analysis from the SIE obtained from action (4) was within the uncertainty. This fact may imply a possible application of thermal analysis for estimating the effect of impurities in the realization of the aluminium point, especially for 6N-grade aluminium fixed-point cell as used in the present study.

In this article, work concerning the thermal analysis of the tin fixed-point is reported. First, the development of a new fixed-point furnace is described. Improvements in the design of the furnace and in the control system enable measurement of the heater power during the phase change. The furnace is sufficiently thermally insulated to produce excellent uniformity and stability, leading to high quality freeze-initiation and minimal thermal influences on the freezing point. By employing the improved furnace and newly-fabricated tin fixed-point cells, the start and end of the melting plateau and the end of the freezing plateau were accurately determined, enabling reliable evaluation of the liquid fraction during the realization of the tin fixed-point compared to conventional methods. Two open-type tin fixed-point cells were fabricated using highpurity tin that was chemically analyzed for impurity content. Thermal analysis results of freezing-point depression are compared to those based on the chemical analysis.

Measurements of the bubble-point pressures and the saturated-liquid densities of the binary mixtures difluoromethane + 1,1,1,2-tetrafluoroethane (R-32 + R-134a) and pentafluoroethane + 1,1,1,2-tetrafluoroethane (R-125 + R-134a) and the ternary mixture difluoromethane + pentafluoroethane + 1,1,1,2tetrafluoroethane (R-32 + R-125 + R-134a) are presented. The estimated uncertainties of (15 mK in temperature, (12 kPa in pressure, (0.2% in density, and (0.3 mol % in composition are reported. The Peng-Robinson equation and the modified Hankinson-Brobst-Thomson equation have been optimized to represent the measured properties satisfactorily. The calculated temperature glides of the mixtures of the present interest have also been presented. IntroductionReplacement of the conventional refrigerant, chlorodifluoromethane (R-22) is one of the urgent issues to be solved within the scheduled time frame of the amended Montreal Protocol. It is well believed that either a binary or ternary refrigerant mixture constituted by R-32, R-125, and/or R-134a would be the optimum candidate to replace R-22. As a continuation to our previous measurements of thermodynamic properties including the bubble-point pressures and saturated-and compressed-liquid densities (liquid PFTx properties) of the binary R-32 + R-134a and R-32 + R-125 (Widiatmo et al., 1993) systems: similar measurements on the binary R-125 + R-134a system and the ternary R-32 + R-125 + R-134a system are reported here along with an evaluation of reliable representations of bubble-point pressures and saturated-liquid densities for industrial applications. Experimental ApparatusAll measurements in the present work were performed with a magnetic densimeter coupled with a variable volume cell which enables measurements either at the saturatedliquid condition or at the compressed-liquid condition. The saturation state of the mixture of the known composition was determined by observing the appearance and disappearance of a bubble in the liquid phase. Since the details of the apparatus have been reported elsewhere (Widiatmo et al., 1993), it will not be repeated in the present paper. By using the present apparatus, the bubble-point pressures were determined with uncertainties within (12 kPa, while the densities were within (0.2%. The uncertainty of temperature and pressure measurements were estimated to be within (15 mK and (12 kPa, respectively, while the determination of the composition of the mixture was done within (0.3 mol %. The purity of the samples analyzed by the manufacturers was 99.998 mass % for R-32, 99.98 mass % for R-125, and 99.8 mass % for R-134a, respectively, and no further purification was performed in the present work. Results and DiscussionThe bubble-point pressures and saturated-and compressed-liquid densities of the binary R-32 + R-134a system are obtained only for compositions of 20, 25, 40, 60, and 80 mass % R-32 (0.3293, 0.3953, 0.5661, 0.7483, and 0.8869 mole fraction of R-32). Those of the binary R-125 + R-134a system are measured for temperatures from 280...