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- Validation of a vibrating-wire viscometer: measurements in the range of 0.5 to 135 mPa'sPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.The present article describes a novel vibrating-wire viscometer that has been shown to be able to measure viscosities up to 135 mPaâs, after calibration against water at 20 °C, to provide direct traceability to the primary reference for viscosity. For the purpose of validating the instrument, measurements of the viscosity of some selected fluids, including standard reference liquids with viscosity on the order of 100 mPaâs at 20 °C and 2,2,4-trimethylpentane with a viscosity of about 0.5 mPaâs at the same temperature, were performed. The results obtained show that the instrument is capable of performing viscosity measurements with an estimated overall uncertainty better than (0.8% over the range of (0.5 to 135) mPa's.
- Viscosity measurements of compressed liquid refrigerant blend R-507A, using a vibrating-wire techniquePublication . Avelino, Helena Maria da Nóbrega Teixeira; Fareleira, João M. N. A.; Oliveira, Carla Padrel deThe refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydrofluorocarbon refrigerants, 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125). The paper reports viscosity measurements, performed with a vibrating-wire viscometer, of the refrigerant blend R-507A,at five temperatures in the range (253 to 293) K. The measurements were carried out at pressures from slightly above saturation up to 10 MPa, except for the isotherms at 253.26 K where the maximum pressure was 7.52 MPa and at 263.23 K where the maximum pressure was 7.09 MPa. The overall uncertainty of these measurements is estimated to be ( 1.0 %. The data obtained were correlated by means of a modified hard-sphere based correlation technique. The root-mean-square deviation, rmsd, of the experimental results from the correlation equations is 0.23 %, and their bias is not significant. This correlation method has also been used to interpolate and extrapolate the present results to enable comparisons with measurements performed by other authors of the viscosity of liquid R-507A at different temperatures and pressures.