Viscosity data are reported for three fluorinated propane isomers in the saturated-liquid state over a combined temperature range from 248 to 348 K. The compounds are -heptafluoropropane (R227ea). The measurements were carried out in sealed gravitational capillary viscometers. The estimated uncertainty of the measurements is (3.4%. Including earlier viscosity measurements on 1,1,1,3,3,3-hexafluoropropane (R236fa) and 1,1,1,2,3,3-hexafluoropropane (R236ea), the viscosity data of all five fluids were correlated within their experimental uncertainty in terms of the rough hard-sphere model. The experimental data were also compared with predictions of the extended corresponding-states method in NIST Standard Reference Database 23 (REFPROP). Deviations range between -20 and 15%.

The saturated-liquid viscosities of 10 binary and ternary refrigerant mixtures composed of difluoromethane (R32), 1,1,1,2-tetrafluoroethane (R134a), pentafluoroethane (R125), and propane (R290) were measured in a sealed gravitational capillary viscometer with a straight vertical capillary from 245 to 345 K or to a maximum vapor pressure of 3 MPa. The maximum uncertainty of the measurements is estimated to be (2.8% for the mixtures of R32 + propane. The largest contribution to the total uncertainty is that of the saturated liquid and vapor densities of the mixtures, which had to be estimated. Comparisons with viscosity data from the literature show agreement within the mutual uncertainty for all but one data set. Similar agreement is found with predicted viscosities using the extended-corresponding-states model in NIST Standard Reference Database 23 (REFPROP), except for the mixtures of the polar fluids R32 and R134a with the nonpolar propane. Their viscosity-composition dependences are strongly nonlinear.

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This paper reports the first wide-ranging application of the free-mode measurement technique to a torsional crystal viscometer. The viscous damping of the fluid on the surface of the crystal is detected in the time domain by observing the freely decaying torsional oscillation of the crystal. Previously, the torsional crystal viscometer was used exclusively in a forced mode of measurement, where the response of the crystal is determined in the frequency domain by scanning through the resonance. The free-decay measurement mode has many advantages over the previous technique. It enables a better characterization of the sensor because the torsional displacement of the crystal can be observed directly. Measurements can be carried out at smaller displacements as well as at constant amplitude in fluid and in vacuo. Direct control over the crystal displacement is an important extension (especially at low external damping of the crystal as in gases or in vacuo), because the measurements can be limited to the linear regime of the crystal vibration and the nonlinear regime can be avoided. In addition, this extension allows for a more complete characterization of the transducer by validating the consistency of its operation in the time and frequency domains. Finally, free-decay measurements are much faster than resonance scans, thus eliminating medium and large time constant variables that can affect the measurement. With these advantages, a second metrological approach has been added to the utilization of torsional crystal viscometers. Sulfur hexafluoride (SF 6) was used as a test fluid to compare the two measurement modes in the presence of external damping. The results of both methods are consistent up to a (viscosity × density) of 0.020 (Pa s)(kg m −3). With improved signal conditioning this limit can be increased substantially. Both measurement techniques were also compared to determine the internal damping of the crystal in vacuo. Nonlinear crystal oscillations were observed which can be interpreted in terms of Duffing and Van der Pol nonlinearities with displacement-dependent stiffness and damping respectively. This insight represents a substantial advance in our understanding of torsional crystal viscometers.

The viscosity of 1,1,1-trifluoroethane (R143a) was measured with a piezoelectrically actuated, torsionally vibrating quartz sensor. The measurements extended over a temperature range from 300 K to 440 K with pressures to 68 MPa and covered states from the dilute gas to the compressed liquid. The influence of the drive voltage on the torsional displacement of the vibrator in fluid and in vacuum was systematically investigated. Since R143a is highly polar, the sample conductance and susceptance were also monitored with the sensor to detect possible electroviscous contributions in the measured viscosities. None were identified so that the estimated uncertainty of the measurements remains at 2 % at a 95 % confidence level (coverage factor = 2). The results agree well within this margin with literature data that were determined with four other viscometric techniques.