Browsing by Author "Santos, Fernando J. V."
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- 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.
- On capillary viscosity measurements: how far do surface tension effects go?Publication . Sequeira, Maria Carolina; Caetano, Fernando J. P.; Diogo, Herminio; Fareleira, João M. N. A.; Santos, Fernando J. V.; Serro, A. P.Viscosity is a fundamental thermophysical property of liquids making it very important particularly in the industry. Capillary viscometers have been widely used for viscosity measurements in different applications, the most relevant being the definition of viscosity standards, traceable to the primary water viscosity standard, by metrological institutions and industrial applications, mostly for quality control. Practical viscometry is based on the internationally accepted primary standard value for the kinematic viscosity of water at 20ºC and atmospheric pressure, which has been measured using capillary viscometers [1]. However, due to the water surface tension, viscosity measurements which have been related to water as a primary standard, can be significantly affected. It is difficult to rigorously assess the surface tension effects on capillary viscometers, and the practical way to avoid this problem is to use long capillaries, which are not appropriate for routine measurements [1-3]. After several experimental studies, using different types of viscometers, the usual procedure to correct surface tension effects in capillary viscosity measurements adopted by different authors, is to employ an empirical expression [1-4]. Additionally, other types of problems exist as the need to perform a kinetic energy correction which must also be taken into consideration [1]. The main goal of this work was to perform the calibration of a suspended-level, or Ubbelohde, capillary viscometer, which is not a long capillary viscometer, as well as the study of corrections to be used for the measurements performed with it. The experimental work covers the calibration of that Ubbelohde capillary viscometer, the evaluation of the uncertainty of the corresponding viscometer constant and the overall uncertainty of the measurements performed with it. This study includes the evaluation of the necessary corrections for kinetic energy and surface tension effects and, finally, the analysis of the case of a set of measurements performed with n-tetradecane. The ultimate purpose of this work is to obtain the lowest uncertainty for the Ubbelohde capillary viscometer 541 01/Ia, and to understand the need for the corrections that must be considered when using capillary viscometers and how they should be applied.
- 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.