Browsing by Author "Pereira, Marta F. V."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
- 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 the viscosity and other properties of poly(Ethylene Glycol) 600Publication . Pereira, Marta F. V.; Santos, Tânia V. M.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.
- 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.
- Viscosity and density measurements on compressed liquid n-TetradecanePublication . Santos, Tânia V. M.; Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.
- Viscosity and density measurements on liquid n-tetradecane at moderately high pressuresPublication . Santos, Tânia V. M.; Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The main aim of the work is to study the viscosity and density of compressed normal tetradecane in the region of pressures from saturation to 10 MPa, where the available literature data are scarce. New measurements of the viscosity of n-tetradecane (n-C-14) along eight isotherms in the range (283-358) K and at pressures up to 70 MPa, have been performed using the vibrating wire technique in the forced mode of operation. Density measurements have also been performed along nine isotherms in the temperature range from (283 to 373) K and pressures from (0.1 to 70) MPa. The vibrating wire viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square (rms) deviation of the data from the correlation is less than 0.32% and the maximum absolute relative deviation is less than 1.0%. The expanded uncertainty of the present viscosity data is estimated as +/- 1.5% at a 95% confidence level. The density results were correlated with the temperature and pressure using a modified Tait equation. The expanded uncertainty of the present density data is estimated as +/- 0.2% at a 95% confidence level. The isothermal compressibility and the isobaric thermal expansion were calculated by differentiation of the modified Tait equation. The uncertainties of isothermal compressibility and the isobaric thermal expansion are estimated to be less than +/- 1.7% and +/- 1.1%, respectively, at a 95% confidence level. The results are compared with the available literature data. (C) 2017 Elsevier B.V. All rights reserved.
- Viscosity measurements of poly(ethyleneglycol) 400 [PEG 400] at temperatures from 293 K to 348 K and at pressures up to 50 MPa using the vibrating wire techniquePublication . Sequeira, Maria Carolina; Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.The article reports new measurements of the viscosity of Poly(ethyleneglycol) 400 [PEG 400] in the range (293–348) K and pressures up to 50 MPa. Complementary measurements of the density of the same sample of PEG 400 have been made covering the ranges of temperature and pressure, (293–353) K and (0.1–50) MPa, respectively. The viscosity measurements were performed using the vibrating wire technique in the forced mode of oscillation and the density measurements were carried out with an Anton Paar vibrating U-tube densimeter. The density raw data were corrected for viscosity effects. The overall uncertainty of the viscosity measurements is estimated to be less than ±2% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an estimated overall uncertainty of ±0.2%. The rheological behaviour of Poly(ethylene Glycol) 400 has also been studied, using a cone-plate Brookfield viscometer, in a temperature range between (293 and 333) K. The measurements were carried out at shear rates up to 20 s−1 and shear stresses up to 2.20 Pa and have evidenced Newtonian behaviour. The viscosity data obtained were correlated by means of a modified hard-sphere based correlation technique. The relative root mean square, rms, deviation of the experimental results from the correlation equations is 0.54%, and their bias is practically zero. The density data obtained were correlated using a Tait-type equation. As a complement of the present study, the surface tension of PEG 400 was measured by the pendant drop method. This study aims to be useful for viscosity measurements using capillary viscometers. As far as the authors are aware, the present viscosity measurements are the first results to be published for PEG 400 at pressures higher than atmospheric pressure.
- Viscosity of liquid diethylene, triethylene and tetraethylene glycols at moderately high pressures using a vibrating wire instrumentPublication . Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.New viscosity measurements of compressed liquid diethylene glycol (DiEG), triethylene glycol (TriEG) and tetraethylene glycol (TeEG) have been performed using a vibrating wire instrument operated in the forced oscillation mode. The measurements have been carried out in a range of pressures up to 70 MPa and temperatures from (293 - 363) K, covering a total range of viscosities from (3.46 - 1.15 x 10^2) mPa,s. Complementary experimental density data were obtained for the same glycols using an Anton Paar vibrating U-tube densimeter. These measurements have been performed in a range of temperatures from about (283 - 363) K and at pressures up to about 70MPa. The viscosity results were correlated with density, using a modified hard-spheres scheme. The experimental density data were correlated, as a function of temperature and pressure, with a modified Tait-type equation. The expanded uncertainty of the present viscosity results at a 95% confidence level is estimated to be less than ±2.0% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an expanded uncertainty of ±0.2% at a 95% confidence level.
- Viscosity of liquid diethylene, triethylene and tetraethylene glycols at moderately high pressures using a vibrating wire instrumentPublication . Pereira, Marta F. V.; Avelino, Helena Maria da Nóbrega Teixeira; Caetano, Fernando J. P.; Fareleira, João M. N. A.New viscosity measurements of compressed liquid diethylene glycol (DiEG), triethylene glycol (TriEG) and tetraethylene glycol (TeEG) have been performed using a vibrating wire instrument operated in the forced oscillation mode. The measurements have been carried out in a range of pressures up to 70 MPa and temperatures from (293–363) K, covering a total range of viscosities from (3.46–1.15 × 102) mPa⋅s. Complementary experimental density data were obtained for the same glycols using an Anton Paar vibrating U-tube densimeter. These measurements have been performed in a range of temperatures from about (283–363) K and at pressures up to about 70 MPa. The viscosity results were correlated with density, using a modified hard-spheres scheme. The experimental density data were correlated, as a function of temperature and pressure, with a modified Tait-type equation. The expanded uncertainty of the present viscosity results at a 95% confidence level is estimated to be less than ±2.0% for viscosities up to 68 mPa s and less than ±2.6% for higher viscosities. The densities have an expanded uncertainty of ±0.2% at a 95% confidence level.