Dana R. Defibaugh

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.

Compressed Liquid Densities and Saturation Densities of Pentafluoroethane (R125)

A vibrating tube densimeter was used to measure the density of pentafluoroethane, R125. Measurements were made between 275 and 369 K, and 1600 and 6300 kPa. Densities ranged between 0.2584 and 1.3484g cm−1 with an accuracy of ± 0.05% except in the near-critical region. A 32 parameter modified Benedict-Webb-Rubin equation of state (MBWR) was fit to the data.

Thermodynamic properties of CF3CHFCHF2, 1,1,1,2,3,3-hexafluoropropane

We report the thermodynamic properties of 1,1,1,2,3,3-hexafluoropropane (known in the refrigeration industry as R236ea or HFC-236ea) in the temperature and pressure region commonly encountered in thermal machinery. The properties are based on measurements of the vapor pressure, the density of the compressed liquid (PVT), the refractive index of the saturated liquid and vapor, the critical temperature, and the speed of sound in the vapor phase. The surface tension was determined from the capillary rise. From these data we deduce the ideal-gas heat-capacity, the saturated liquid and vapor densities, the equation of state of the vapor phase, the surface tension, and estimates of the critical pressure and density. The data determine the coefficients for a Carnahan-Starlings-DeSantis (CSD) equation of state. The CSD coefficients found in REFPROP 4.0 database are based on these present measurements.

The virial coefficients of five binary mixtures of fluorinated methanes and ethanes

We have made new measurements of the gas-phasePVT surface of five binary mixtures of hydrofluorocarbons (HFCs) in a Burnett/isochoric apparatus. The components chosen all have moderate to large reduced dipole moments. We presentPVT data, derived mixture virial coefficients, cross second virial coefficients, and binary interaction parameters for these systems, and we compare the results with a recently published model for calculating second and third viral coefficients of polar gases and their mixtures. That model accounts for the polar nature of the molecules with a term containing the reduced dipole moment,μR, and it contains mixing rules for the substance-specific parameters needed to calculate the second and third cross virial coefficients. The model and data are in satisfactory agreement. and the model can be used to greatly extend the useful range of the limited set of data.

Thermodynamic properties of CHF2-O-CHF2, bis(difluoromethyl) ether

Abstract Defibaugh, D.R., Gillis, K.Aa Moldover M.R., Morrison, G. and Schmidt, J.W., 1992. Thermodynamic properties of CHF2-O-CHF2, bis(difluoromethyl) ether. Fluid Phase Equilibria, 81: 285–305. We have measured the thermodynamic properties of bis(difluoromethyl) ether, CHF2-O- CHF2, a candidate alternative refrigerant that is also known as E134. From the data we obtained the coefficients of a Carnahan-Starling-DeSantis equation of state and a polyno- mial representation of the ideal-gas heat capacity. This representation of the thermodynamic properties of E134 is consistent with the computer package REFPROP distributed by the National Institute of Standards and Technology to represent the properties of many candidate refrigerants. The representation is based on measurements of the refractive index of the saturated liquid and vapor, and the speed of sound of the dilute vapor. These measurements provide the boiling point, critical parameters, and the ideal-gas heat capacity of E134. Measurements on less pure samples were used to estimate the density of saturated liquid E134 and compressed liquid E134, and the interfacial tension. The pure samples appeared to be stable during the measurements; under similar conditions impure samples were not. Azeotropy in mixtures of E134 with CHF2CH2F (also known as R143) was discovered.

Thermodynamic properties of CHF2CF2CH2F, 1,1,2,2,3-pentafluoropropane

Abstract We report the thermodynamic properties of 1,1,2,2,3-pentafluoropropane (known in the refrigeration industry as HFC-245ca) in the temperature and pressure region commonly encountered in thermal machinery. The properties are based on measurements of the vapor pressure, the density of the compressed liquid, the refractive index of the saturated liquid and vapor, the critical temperature, the speed of sound in the vapor phase, and the capillary rise. From these data we deduce the saturated liquid and vapor densities, the equation of state of the vapor phase, the surface tension, and estimates of the critical pressure and density. The data determine the coefficients for a Carnahan-Starlings-DeSantis (CSD) equation of state. The CSD coefficients found in REFPROP 4.0 are based on the measurements reported here.

Thermodynamic properties of 1,1-dichloro-1-fluoroethane (R141b)

Abstract Defibaugh D.R., Goodwin A.R.H., Morrison G. and Weber L.A., 1993. Thermodynamic properties of 1,1-dichloro-1-fluoroethane (R141b). Fluid Phase Equilibria 85: 271-284. Thermodynamic properties of 1,1-dichloro-1-fluoroethane (R141b) were measured using a vibrating-tube densimeter and two different ebulliometric techniques. The densimeter was used to measure compressed liquid densities, and the ebulliometers were used to study the vapor pressure. Measurements of the density were made between 278 and 369 K and between 100 and 6000 kPa. The vapor pressure was measured from 253 to 355 K at pressures from 10 to 449 kPa. Both the compressed liquid and the vapor pressure results are compared with other published data. Our results for the vapor pressure have been combined with results already published to obtain a correlation for the vapor pressure from 253 K to the critical point.

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123)

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123) has been measured at temperatures between 256.4 and 453.8 K by ebulliometric and static techniques. These results have been combined to obtain a correlation for the vapor pressure from 256.4 K to the critical temperature.

Progress in Primary Acoustic Thermometry at NIST: 273 K to 505 K

The NIST Acoustic Thermometer determines the thermodynamic temperature by measuring the speed of sound of argon in a spherical cavity. We obtained the thermodynamic temperature of three fixed points on the International Temperature Scale of 1990: the melting point of gallium [T(Ga) = 302.9146 K] and the freezing points of indium [T(In) = 429.7485 K] and tin [T(Sn) = 505.078 K]. The deviations of thermodynamic temperature from the ITS‐90 defined temperatures are T − T90 = (4.7 ± 0.6) mK at T(Ga) , T − T90 = (8.8 ± 1.5) mK at T(In) , and T − T90 = (10.7 ± 3.0) mK at T(Sn) , where the uncertainties are for a coverage factor of k = 1. Our results at T(In) and T(Sn) reduce the uncertainty of T − T90 by a factor of two in this range. Both T − T90 at T(Ga) and the measured thermal expansion of the resonator between the triple point of water and T(Ga) are in excellent agreement with the 1992 determination at NIST. The dominant uncertainties in the present data come from frequency‐dependent and time‐dependent cros...

Techniques for Primary Acoustic Thermometry to 800 K

The NIST Primary Acoustic Thermometer will measure the difference between the International Temperature Scale of 1990 and the Kelvin Thermodynamic Scale throughout the range 273 K to 800 K with uncertainties of only a few millikelvins. The acoustic thermometer determines the frequencies of the acoustic resonances of pure argon gas contained within a spherical cavity with uncertainties approaching one part in 106. To achieve this small uncertainty at these elevated temperatures we developed new acoustic transducers and new techniques for the maintenance of gas purity and for temperature control. The new electro‐acoustic transducers are based on the capacitance between a flexible silicon wafer and a rigid backing plate. Without the damping usually provided by polymers, mechanical vibrations caused unstable, spurious acoustic signals. We describe our techniques for suppression of these vibrations. Our acoustic thermometer allows the argon to be continuously flushed through the resonator, thereby preventing t...