DOE/CE/23810-16 THERMOPHYSICAL PROPERTIES Final Report 1 January 1992 - 31 March 1993 Richard F. Kayser Thermophysics Division Building 221, Room A105 National Institute of Standards and Technology Gaithersburg, Maryland 20899 April 1993 Prepared for The Air-Conditioning and Refrigeration Technology Institute Under ARTI MCLR Project Number 650-50800 This research project is supported, in whole or in part, by U.S. Department of Energy grant number DE-FG02-91CE23810: Materials Compatibility and Lubricants Research (MCLR) on CFC-Refrigerant Substitutes. Federal funding supporting this project constitutes 93.67% of allowable costs. Funding from non-government sources supporting this project consists of direct cost sharing of 6.33% of allowable costs; and in-kind contributions from the air-conditioning and refrigeration industry. DISCLAIMER The U.S. Department of Energy's and the air-conditioning industry's support for the Materials Compatibility and Lubricants Research (MCLR) program does not constitute an endorsement by the U.S. Department of Energy, nor by the air-conditioning and refrigeration industry, of the views expressed herein. NOTICE This report was prepared on account of work sponsored by the United States Government. Neither the United States Government, nor the Department of Energy, nor the Air Conditioning and Refrigeration Technology Institute, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product or process disclosed or represents that its use would not infringe privately- owned rights. COPYRIGHT NOTICE (for journal publication submissions) By acceptance of this article, the publisher and/or recipient acknowledges the right of the U.S. Government and the Air-Conditioning and Refrigeration Technology Institute, Inc. (ARTI) to retain a nonexclusive, royalty-free license in and to any copyrights covering this paper. i DOE/CE/23810-16 THERMOPHYSICAL PROPERTIES ARTI MCLR Project Number 650-50800 Richard F. Kayser Thermophysics Division National Institute of Standards and Technology ABSTRACT Numerous fluids have been identified as promising alternative refrigerants, but much of the information needed to predict their behavior as pure fluids and as components in mixtures does not exist. In particular, reliable thermophysical properties data and models are needed to predict the performance of the new refrigerants in heating and cooling equipment and to design and optimize equipment to be reliable and energy efficient. The objective of this fifteen-month project has been to provide highly accurate, selected thermophysical properties data for Refrigerants 32, 123, 124, and 125, and to use these data to fit equations of state and transport property models. The new data have filled gaps in the existing data sets and resolved problems and uncertainties that existed in and between the data sets. SCOPE This project has involved selected measurements of the thermodynamic properties of HFC- 32, HCFC-124, and HFC-125, and the development of high-accuracy modified Benedict-Webb- Rubin (MBWR) equations of state for each fluid. It has also included selected measurements of the transport properties of HFC-32 (viscosity and thermal conductivity) and HCFC-123 (thermal conductivity) and the development of detailed correlations for same. The experimental thermodynamic measurements have included, as appropriate, accurate determinations of the pressure-volume-temperature (PVT) behavior in the superheated vapor region; the PVT behavior of the compressed liquid; vapor pressures and saturated liquid densities; the critical temperature, pressure, and density; the vapor-phase speed of sound and the ideal-gas heat capacity; and selected measurements of the liquid-phase heat capacity. The experimental transport measurements have covered one-phase and saturated liquid and vapor states over the temperature range of interest. SIGNIFICANT RESULTS HFC-32 The Burnett apparatus has been used in the isochoric mode to determine the PVT relation for the vapor phase (147 data points). Eleven isochores were completed spanning the ranges 268 to 373 K (23 to 212°F) and 0.018 to 1.3 times the critical density (7.5 to 550 kg/m3; 0.47 to 34.3 lb/ft3); the highest absolute pressure was 9.7 MPa (1400 psi). Two Burnett expansions were completed at 373 K (212°F) to establish the densities of the isochores. The locations of 1 the measurements are indicated as a function of pressure and temperature by the filled circles on Figure 1, and as a function of density and pressure by the filled circles on Figure 2. The results of the measurements are given in Appendix A in Table 1; Appendix A includes all tables. The vibrating tube densimeter has been used to determine the PVT relation for the liquid phase (654 data points). Twenty-one isotherms were completed spanning the ranges 243 to 343 K (-22 to 158°F) and 2000 to 6500 kPa (290 to 940 psi). The locations of the measurements are indicated as a function of pressure and temperature by the open circles on Figure 1, and as a function of density and pressure by the open circles on Figure 2. The results of the measurements are given in Table 2. An isochoric PVT apparatus has been used to measure the density of liquid HFC-32 at 144 points using the same sample as used in the Cv study (see below). The temperatures ranged from 140 to 396 K (-208 to 253 °F) with pressures to 35 MPa (5000 psi). The locations of the measurements are shown in Figure 3, and the results are presented in Table 3. The Burnett apparatus has been used to measure the vapor pressure of HFC-32 at 18 temperatures in the range from 268 K (23°F) to the critical temperature at 351.36 K (172.78°F). The results of these measurements are given in Table 4. An ebulliometer has been used to measure the vapor pressure of HFC-32 at low temperatures in the range between 208 and 237 K (-85 and -32°F). The results are tabulated in Table 5. The NIST Burnett and ebulliometric vapor-pressure data for HFC-32 have been correlated and their deviations from the resulting correlation are shown in Figure 4. Also shown in Figure 4 are the HFC-32 data of P.F. Malbrunot, et al. [J. Chem. & Eng. Data 13, 16 (1968)]. The uncertainties in the NIST measurements are of order 0.05 %. The saturated vapor and liquid densities have been obtained by extrapolating the Burnett vapor-phase and vibrating-tube liquid-phase PVT data to the vapor pressure curve. The saturated vapor and liquid densities so obtained are given in Tables 6 and 7, respectively. A static method has been used to perform additional measurements of the vapor pressure of HFC-32. The sample was thermostatted in the PVT cell and two additional oscillating quartz- crystal pressure transducers were used to observe the equilibrium pressures. The two transducers, with maximum pressures of 0.2 MPa (30 psi) and 6 MPa (900 psi), were calibrated versus a gas-lubricated piston gage with an uncertainty of ± 0.01 %. The range of the vapor pressure data is from 140 to 340 K (-208 to 152°F). These results are given in Table 8. An optical cell has been used to measure the refractive index and capillary rise of HFC-32 from 23°C (73°F) up to the critical temperature. The critical temperature was found to be Tc = (351.36 ± 0.02) K, which corresponds to (172.78 ± 0.04)°F. The refractive index data were combined with the liquid density data to deduce the value 0.1295 cm3/g for the Lorentz-Lorenz constant. The refractive index data and the Lorentz-Lorenz constant were used to deduce the 3 3 value rc = (419 ± 7) kg/m [(26.13 ± 0.44) lb/ft ] for the critical density. An adiabatic calorimeter has been used to measure the molar heat capacity at constant volume {Cv}for HFC-32. In total, 79 Cv values were measured in the liquid state and 105 2 values were measured in the vapor + liquid two-phase region. The temperatures ranged from 141 to 342 K (-206 to 156°F), with pressures up to 35 MPa (5000 psi). The measured values are given in Tables 9 through 16 for the liquid phase and in Tables 17 through 19 for the two-phase region. In addition to the temperature-density-pressure (T-r-P) state conditions, the tables present estimated uncertainties of the measurements which lead to values of liquid heat capacity, Cv, or heat capacity of the saturated liquid, Cs. These measurements include the amount of sample, N, the calorimeter bomb volume, Vbomb, the observed temperature rise, DT, the energy absorbed, Qtare, and the heat capacity, dQtare/dT, of the empty calorimeter bomb, gross heat capacity, Q/DT, and the PV work done by the sample to expand the bomb during a heat capacity measurement, Wpv,m. Figure 5 illustrates the pressures and temperatures covered by this study. A 32-term MBWR equation of state for HFC-32 has been developed. It is valid at temperatures from the triple point at 137 K (-213 °F) to 400 K (260°F), and it appears to be reasonable upon extrapolation up to 500 K (440°F). The maximum pressure for the equation is 40 MPa (6000 psi), and it appears to be reasonable upon extrapolation up to 100 MPa (15000 psi). This equation was fit using a multiparameter linear least squares routine to the data measured under this contract as well as selected data reported in the literature. Data used in the fit included vapor pressures, saturated liquid and vapor densities, liquid and vapor phase pressure-volume-temperature (PVT) data, virial coefficients, and isochoric heat capacities at saturation and in the single-phase liquid.