Browsing by Author "Wakeham, William A."
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- An industrial reference fluid for moderately high viscosityPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fröba, Andreas P.; Harris, Kenneth R.; Leipertz, Alfred; Trusler, J. P. Martin; Wakeham, William A.In industrial practice, there is a demand for a reference standard for viscosity that is established for a readily available fluid to simplify the calibration of industrial viscometers for moderately high viscosities [(50 to 125) mPa · s]. Diisodecyl phthalate (DIDP) has been suggested as that reference fluid, and a number of studies of its properties have been carried out in several laboratories throughout the world, within the auspices of a project coordinated by the International Association for Transport Properties. That project has now progressed to the point where it is possible to collate the results of studies of the viscosity of the fluid by a number of different techniques, so as to lead to a proposed standard reference value which will be included in the paper. To support this recommended value, the various measurements conducted have been critically reviewed, and the sample purity and other factors affecting the viscosity have been studied. Density and surface tension measurements have also been performed. This paper does not describe the individual viscosity determinations carried out in independent laboratories because these are the subject of individual publications, but it does describe the ancillary studies conducted and their relevance to the viscosity standard. In addition, the paper contains recommended values for the viscosity of liquid DIDP. The samples of DIDP to which the recommended values refer are isomeric mixtures available commercially from certain suppliers, with a minimum purity by gas chromatography of 99.8 %. The recommended values result from a critical examination of all the measurements conducted to date and are supported by careful arguments dealing with the likely effects of the isomeric content of the sample as well as of other impurities. The proposed reference standard is intended particularly to serve an industrial need for a readily available calibration material with a viscosity close to that required in practical situations. To that end, the recommended value has an overall relative uncertainty of approximately 1 %. It is therefore not intended to supersede for the reference value for the viscosity of water at 20 °C, which is known much more accurately, but rather to complement it.
- Density and Rheology of Tris(2-ethylhexyl) Trimellitate (TOTM)Publication . Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Diogo, João C. F.; Fareleira, João M. N. A.; Pereira, Marta F. V.; Santos, Fernando J. V.; Santos, Tânia V. M.; Wakeham, William A.This article presents new density data and some rheological studies on tris(2-ethylhexyl) trimellitate (TOTM) which has recently been proposed as a reference fluid for viscosity at high temperatures and high pressures. The density data have been obtained with the aid of an Anton Paar DMA HP U-tube instrument, covering temperatures from 328 to 423 K and pressures up to 70 MPa, and they are aimed at extending the temperature range of previous results. They are also used to check the effect of interlot consistency of the density data for TOTM. The present density measurements are compared with previously published data. Rheological tests were carried out to complement earlier studies. Particular attention is given to the shear rate range of greatest interest for the proposed use of TOTM as an industrial reference fluid for viscosity: the tests include shear stresses up to 750 Pa and shear rates up to 4000 s–1 under atmospheric pressure. The tests were carried out using a Parallel Plate Rheometer AR1500ex10C4298. The results at a temperature of 298 K corroborate the previous findings that TOTM is Newtonian below a shear rate of 600 s–1, which is entirely compatible with its use as an industrial calibrating fluid for viscosity. At shear rates higher than 600 s–1 a shear-thinning like behavior is observed.
- Diisodecylphthalate (DIDP) — a potential standard of moderate viscosity: surface tension measurements and water content effect on viscosityPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Fernandes, Anabela C.; Serro, Ana P.; Almeida, Inês M. Simões de; Wakeham, William A.Our laboratory, along with several others, has been engaged in a project to determine the suitability of diisodecylphthalate (DIDP) as a standard reference material of viscosity for industrial purposes. As a part of that project, we have undertaken a study of the effects of surface tension and of impurities, of that liquid on viscosity measurements with routine, suspended level capillary instruments. For the former purpose, a set of surface tension measurements is reported here for DIDP and two reference standard mineral oils. In particular, surface tension data for DIDP, obtained using a pendant-drop shape-analysis method, at temperatures from 288K to 308K are presented. The present study suggests that surface tension effects upon viscosity measurements with routine capillary viscometers can be important enough to demand that the surface tension of the reference fluid(s) used for their calibration be specified. It is also evident that the surface tension of materials used for calibration may be relevant to their selection if errors arising from surface tension are to be avoided. In order to fulfil these requirements, the surface tension of the reference material should be included in the definition of the standard. The effect of the water content on the viscosity of a sample of DIDP is assessed as a part of the process of determining its suitability as a standard reference material.
- In pursuit of a high temperature, high pressure, high viscosity standard: the case of TOTM!Publication . Wakeham, William A.; Assael, Marc J.; Avelino, Helena Maria da Nóbrega Teixeira; Bair, Scott; Bamgbade, Babatunde A.; Bazile, Jean-Patrick; Baled, Hseen O.; Caetano, Fernando J. P.; Comuñas, M. J .P.; Daridon, J.-L.; Diogo, João C. F.; Enick, Robert M.; Fareleira, João M. N. A.; Fernandez, J.; Oliveira, M. C.; Santos, T.; Tsolakidou, Ch. M.Excel file for the viscosity and density calculation for Tris(2-ethylhexyl) trimellitate (TOTM), CAS 3319-31-1, a liquid being proposed as a high viscosity at high pressure and high temperature industry standard fluid.
- In pursuit of a high-temperature, high-pressure, high-viscosity standard: the case of Tris(2-ethylhexyl) TrimellitatePublication . Wakeham, William A.; Assael, Marc J.; Avelino, Helena Maria da Nóbrega Teixeira; Bair, Scott; Baled, Hseen O.; Bamgbade, Babatunde A.; Bazile, Jean-Patrick; Caetano, Fernando J. P.; Comunas, Maria J. P.; Daridon, Jean-Luc; Diogo, João C. F.; Enick, Robert M.; Fareleira, João M. N. A.; Fernandez, Josefa; Oliveria, M. Conceicao; Santos, Tânia V. M.; Tsolakidou, Chrysi M.This paper presents a reference correlation for the-viscosity of tris(2-ethylhexyl) trimellitate designed to serve in industrial applications for the calibration of viscometers at elevated temperatures and pressures such as those encountered in the exploration of oil reservoirs and in lubrication. Tris(2-ethylhexyl) trimellitate has been examined with respect to the criteria necessary for an industrial standard reference material such as toxicity, thermal stability, and variability among manufactured lots. The viscosity correlation has been based upon all of the data collected in a multinational project and is supported by careful measurements and analysis of all the supporting thermophysical property data that are needed to apply the standard for calibration to a wide variety of viscometers. The standard reference viscosity data cover temperatures from 303 to 473 K, pressures from 0.1 to 200 MPa, and viscosities from approximately 1.6 to 755 mPa s. The uncertainty in the data provided is of the order of 3.2% at 95% confidence level, which is thought to be adequate for most industrial applications.
- A new instrument to perform simultaneous measurements of density and viscosity of fluids by a dual vibrating-wire techniquePublication . Oliveira, Carla Padrel de; Mata, José L. Correia da; Fareleira, João M. N. A.; Caetano, Fernando J. P.; Wakeham, William A.A preliminary presentation of a new vibrating-wire instrument for the simultaneous measurement of the viscosity and density of fluids, over wide ranges of temperature and pressure, is made. The new equipment has the capability of measuring modes of oscillation, either in a forced mode or free decay. A theoretical description of both modes enables the simultaneous measurement of the viscosity and density of the fluid, either from an analysis of the resonance curve, or the transient response of the sensor. The consistency of the two approaches, under the same working conditions, and quality of the measuring system, have been assessed with toluene as the test fluid. It is concluded that the new equipment improves the forced mode of operation described earlier and adds a new flexibility to the vibrating-wire method.
- Quest for a reference standard for viscosity at high temperatures and high pressuresPublication . Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Diogo, João C. F.; Fareleira, João M. N. A.; Pereira, Marta F. V.; Santos, Fernando J. V.; Santos, Tânia V. M.; Wakeham, William A.This communication is dedicated to give notice of the present situation concerning the proposal of tris(2-ethylhexyl) trimellitate (TOTM) to be a reference standard fluid for viscosity at high temperatures and high pressures. This proposal stems from an internal project of the International Association for Transport Properties (IATP). A general overview of the efforts carried out so far by the scientific community towards that objective will be made. This will be complemented by a description of its main characteristics that support its proposal. In particular, the present work is concerned with the determination of the shear dependence of the viscosity of TOTM. Moreover, new results for the density of TOTM at moderately high temperatures and pressures up to 70 MPa are presented.
- 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 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.
- 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.
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