Hydrocarbons (HCs) are environmentally friendly natural refrigerants and are expected to be promising alternative candidates to replace some currently used halogenated hydrocarbon refrigerants. Some available data sets for HCs used to formulate the equations of state (EoS) for them are relatively old, so we point out that new data with less uncertainty are expected to play an essential role in updating the EoS for HCs. Therefore, a set of PVT property measurements for hydrocarbon refrigerants including propane, n-butane, and isobutane was conducted in the present study. A newly developed vibrating-tube densimeter was employed for the measurements, and then a total of 430 liquid PVT properties were obtained, including those at the saturation boundaries. The measurement range is (240 to 380) K for temperature and up to 7 MPa for pressure. The measurement uncertainty is about 3 mK for temperature, 0.26 kPa + 0.022% for pressure, and 0.1 kg‚m -3 + 0.024% for density. The present data were compared with available thermodynamic models that are currently considered to be the most reliable. A set of modified Tait equations of state for the liquid phase are also discussed.

Concerning an increasing demand for environmentally friendly refrigerants including hydrocarbons, thermodynamic properties of such new refrigerants, especially densities, are essential information for refrigeration engineering. A rapid density-measurement system with vibrating-tube densimeter was developed in the present study with an aim to supply large numbers of high-quality PVT property data in a short period. The present system needs only a few minutes to obtain a single datum, and requires less than 20 cm3 sample fluid. PVT properties in the entire fluid-phase, vapor-pressures, saturated-liquid densities for pure fluid are available. Liquid densities, bubble-point pressures and saturated-liquid densities for mixture can be obtained. The measurement range is from 240 to 380 K for temperature and up to 7 MPa for pressure. By employing a new calibration function, density can be precisely obtained even at lower densities. The densimeter is calibrated with pure water and iso-octane which is one of the density-standard fluids, and then measurement uncertainty was evaluated to be 0.1 kg m−3 or 0.024% whichever greater in density, 0.26 kPa or 0.022% whichever greater in pressure and 3 mK for temperature, respectively. The performance of the present measurement system was examined by measuring thermodynamic properties for refrigerant R134a. The experimental results were compared with available equation of state and confirmed to agree with it within ±0.05% for liquid densities while ±0.5% in pressure for the gas phase.

Experimental thermodynamic property data for hydrocarbon refrigerant mixtures are more important now in order to improve the performance of existing equations of state. In the present paper, liquid-phase PVTx data including bubble points for the binary and ternary systems composed of propane (1), n-butane (2), and isobutane (3) are reported. More than 1000 measurements were made by employing a newly developed vibrating-tube densimeter system with an uncertainty of 0.1 kg·m-3 + 0.024% for density, (3 to 7) mK for temperature, 0.26 kPa + 0.022% for pressure, and 0.1 mol % for composition. The present data contain the first set of experimental PVTx data for the ternary system. The measured data are compared with two available thermodynamic mixture models developed by Lemmon and Jacobsen and Miyamoto and Watanabe. A mixture model applied for a modified Tait equation of state is also presented in this paper.

PVT properties are presented for both the gas-phase and liquid-phase, vapor pressures and saturated-liquid densities for hydrofluoroether (HFE) refrigerants, trifluoromethyl methyl ether (CF3OCH3) and pentafluoroethyl methyl ether (C2F5OCH3), that were obtained with a Burnett apparatus and a vibrating-tube densimeter. A total of 250 liquid densities and 70 gas-phase PVT properties for CF3OCH3 and 281 liquid densities and 125 gas-phase PVT properties for C2F5OCH3 were obtained in wide ranges of temperature (240 to 380) K and pressure up to 7 MPa with a rapid density measurement system with a vibrating-tube densimeter. For CF3OCH3, 109 gas-phase PVT properties were obtained with a Burnett apparatus at the temperatures (300 to 380) K and up to nearly the critical density. On the basis of the present measurements, we have also developed thermodynamic models to complement the experimental data. Equations of state for the liquid phase and truncated virial equations of state are discussed in this paper, as well as a couple of correlations for vapor pressures and saturated-liquid densities.

More than 2000 PVT data in the liquid phase, vapor phase, and at saturation boundaries have been obtained for pure compounds of several alternative refrigerants. In addition, more than 1000 liquid-density data have been obtained for several binary and ternary mixtures. The alternative refrigerants measured in the present study include CF 3 OCH 3 (trifluoromethyl methyl ether) and CF 3 CF 2 OCH 3 (pentafluoroethyl methyl ether), which are hydrofluoroethers developed by RITE (the Research Institute of Innovative Technology for the Earth, Japan), and typical hydrocarbons, such as propane, n-butane, isobutene, and their binary and ternary mixtures. The measurement uncertainties are estimated to be 3 to 7 mK for temperature, 0.26 kPa or 0.022% whichever is greater for pressure, and 0.07 kg · m −3 or 0.024% whichever is greater for density. The present measurement system took only a few minutes to get one PVT datum, and one or two days to complete all the measurements for a single fluid at temperatures from 240 to 380 K and at pressures up to 7 MPa. In addition, an empirical equation of state (EoS) for the liquid phase was developed on the basis of the present data, and the EoS nicely reproduces not only the present data but also existing data reported by other researchers.