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- The viscosity of five liquid hydrocarbons at pressures up to 250 MPaPublication . Oliveira, Carla Padrel de; Wakeham, William A.This paper reports new measurements of the viscosity of toluene, n-pentane, n-hexane, n-octane, and n-decane at pressures up to 250 MPa in the temperature range 303 to 348 K. The measurements were performed with a vibrating-wire viscometer and with a relative method of evaluation. Calibration of the instrument was carried out with respect to reference values of the viscosity of the same liquids at their saturation vapour pressure. The viscosity measurements have a precision of _0.1% but the accuracy is limited by that of the calibration data to be +0.5%. The experimental data have been represented by polynomial functions of pressure for the purposes of interpolation. The data are also used as the most precise test yet applied to a representation of the viscosity of liquids based upon hard-sphere theory.
- The viscosity of R32 and R125 at saturationPublication . Oliveira, Carla Padrel de; Wakeham, William A.This paper reports new measurements of the viscosity of R32 and R125, in both the liquid and the vapor phase, over the temperature range 220 to 343 K near the saturation line. The measurements in both liquid and vapor phases have been carried out with a vibrating-wire viscometer calibrated with respect to standard reference values of viscosity. It is estimated that the uncertainty of the present viscosity data is one of 0.5-1%, being limited partly by the accuracy of the available density data. The experimental data have been represented by polynomial functions of temperature for the purposes of interpolation.
- Vibrating-wire viscometry on liquid hydrocarbons at high pressurePublication . Oliveira, Carla Padrel de; Assael, Marc J.; Papadaki, Maria; Richardson, Stephen M.; Wakeham, William A.A vibrating-wire viscometer for the measurement of the viscosity of liquids at elevated pressures is described. The instrument is one of a pair, developed collaboratively in different laboratories, that operate in a relative manner according to a complete theory of the instrument. The instrument described here has been used for measurements at pressures up to 80 MPa in toluene, and in n-heptane along two isotherms.
- Vibrating-wire viscometers for liquids at high pressuresPublication . Oliveira, Carla Padrel de; Assael, Marc J.; Papadaki, Maria; Wakeham, William A.The design and operation of two independent vibrating-wire viscometers are described. The instruments are intended for operation in the liquid phase at pressures up to 300 MPa and have been designed specifically for this purpose using the detailed theory of the device. Extensive evidence is adduced to demonstrate that the operation of the viscometers is consistent with the theory. Although the instruments attain a precision in viscosity measurements of __+1% when used in an absolute mode the accuracy that can be achieved is no better than __+3%. However, if the instrument is calibrated for two welldefined instrumental parameters, the uncertainty in the reported viscosity is improved to _+0.5%. The results of measurements of the viscosity of normal heptane in the temperature range 303 to 348 K at pressures up to 250 MPa made with one of the viscometers are reported. The results are shown to be totally consistent with measurements reported earlier using the instrument designed for lower pressures.
- The viscosity of liquid R134aPublication . Oliveira, Carla Padrel de; Wakeham, William A.The paper reports new measurements of the viscosity of liquid R134a over the temperature range 235 to 343 K and pressures up to 50MPa. The measurements have been carried out in a vibrating-wire viscometer calibrated with respect to the viscosity of several liquid hydrocarbons. It is estimated that the uncertainty in the viscosity data reported is +0.6%. The data therefore have a lower uncertainty than that of earlier measurements of the viscosity of this environmentally acceptable regrigerant. The viscosity data have been represented as a function of density by means of a formulation based upon the rigid, hard-sphere theory of dense fluids with a maximum deviation of _+0.3%. This representation allows the present body of experimental data to be extended to regions of thermodynamic state not covered by the measurements.
- Viscosity of new refrigerantsPublication . Oliveira, Carla Padrel de; Wakeham, William A.Measurements of the viscosity of several environmentally-acceptable refrigerants that have been made in recent years are reviewed. In particular, a detailed survey of the results for R134a in the liquid phase is presented because, for this fluid, the greatest number of independent experimental results is available. It is shown that there are significant discrepancies between the results of various authors and that they lie outside the bounds of the mutual uncertainty claimed. The nature of the discrepancies between any two sets of results is shown to be systematic whether they have been performed in similar or different types of instrument. For R32 and R125 in the liquid phase, where there are very many fewer experimental results available, the situation is essentially the same. It is argued that these discrepancies arise from a lack of proper precautions in the performance of the measurements either because of difficulties associated with the purity of the samples employed or because, in some instruments, there has been insufficient attention devoted to discrepancies among the results of research workers with established records of high-quality measurements are damaging to the external perception of the science of viscometry and that remedial action to remove the difficulties is essential and urgent. Specific recommendations for such action are made.
- Viscosity of R134a, R32, and R125 at saturationPublication . Oliveira, Carla Padrel de; Wakeham, William A.This paper reports the results of the measurement of the viscosity of R134a close to the saturation line in the vapor phase. The new measurements were carried out in a vibrating-wire viscometer specially constructed for the purpose, and the results have an accuracy of ±2%. In addition, the opportunity is taken to present a reevaluation of earlier measurements along the saturation line of the viscosity of R32 and R125. Improved equations of state for these fluids are now available and can be employed to generate improved values for the viscosity.