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- 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.
- Thermophysical property measurements: the journey from accuracy to fitness for purposePublication . Oliveira, Carla Padrel de; Wakeham, William A.; Assael, Marc J.; Atkinson, J. K.; Bilek, J.; Fareleira, João M. N. A.; Fitt, A. D.; Goodwin, A. R. H.Until the 1960s much of the experimental work on the thermophysical properties of fluids was devoted to the development of methods for the measurement of the properties of simple fluids under moderate temperatures and pressures. By the end of the 1960s a few methods had emerged that had both a rigorous mathematical description of the experimental method and technical innovation to render measurements precise enough to rigorously test theories of fluids for both gas and liquid phases. These studies demonstrated that, for the gas phase at least, the theories were exceedingly reliable and led to physical insight into simple molecular interactions. The thesis of this paper is, after those early successes, there has been a divergence of experimental effort from the earlier thrust and, in the future, there needs to be focus on in situ measurement of properties for process fluids. These arguments are based upon the balance between the uncertainty of the results and their utility and economic value as well as upon technical developments, which have provided reliable and robust sensors of properties. The benefits accrued from accurate measurements on a few materials to validate predictions of the physical properties, for a much wider set of mixtures over a wide range of conditions, are much less relevant for most engineering purposes. However, there remain some special areas of science where high accuracy measurements are an important goal.