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- New measurements of the viscosity of diisodecyl phthalate using a vibrating wire techniquePublication . Oliveira, Carla Padrel deDiisodecyl phthalate (DIDP) has been proposed as a suitable reference material for industrial application in the region of moderately high viscosity. The paper reports a new set of viscosity measurements of a 99.5 % GC sample of this substance, which are directly traceable to the primary standard reference values the viscosity of water at 293.15 K. The present measurements, performed with a vibrating-wire sensor, were carried out at atmospheric pressure over the temperature range (283 to 313) K. Over this temperature range, the viscosity varies from approximately (37 to 267) mPaâs. The measurements have been carried out with an instrument that has already been the subject of improvement since the first measurements were performed, and it relies upon calibration exclusively against the primary standard of viscometry. The estimated overall uncertainty of the results does not exceed ( 1 %, over the whole range of the measurements and, for the results obtained at temperatures in the vicinity of 293 K, is ( 0.8 %. The higher quality of the present measurements, and their direct traceability to the primary reference value for viscosity, justifies the replacement of our earlier set of preliminary data on DIDP viscosity.
- 2008 Ano Internacional do Planeta Terra: Terra, saúde e alterações climáticasPublication . Amador, Filomena; Oliveira, Carla Padrel de; Cardoso, Abel; Antunes, Ana PaulaAs causas ambientais de alguns problemas de saúde, relação entre alterações climáticas e saúde e as dinâmicas de algumas doenças emergentes no quadro das relações humanas com o meio ambiente. Visita ao Jardim Tropical de Lisboa, com os Professores Carla Oliveira, docente da Universidade Aberta e Jorge Atouguia, médico especialista em Medicina Tropical.
- Química geral : reactividade químicaPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Antunes, Elisa; Leão, HelenaO vídeo trata as reações de oxiredução e as reações de complexação. São explicados e exemplificados os conceitos de redutor, oxidante, elemento de pilha e pilha eletroquímica.
- Validation of a vibrating-wire viscometer: measurements in the range of 0.5 to 135 mPa'sPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.The present article describes a novel vibrating-wire viscometer that has been shown to be able to measure viscosities up to 135 mPaâs, after calibration against water at 20 °C, to provide direct traceability to the primary reference for viscosity. For the purpose of validating the instrument, measurements of the viscosity of some selected fluids, including standard reference liquids with viscosity on the order of 100 mPaâs at 20 °C and 2,2,4-trimethylpentane with a viscosity of about 0.5 mPaâs at the same temperature, were performed. The results obtained show that the instrument is capable of performing viscosity measurements with an estimated overall uncertainty better than (0.8% over the range of (0.5 to 135) mPa's.
- 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.
- Química geral : velocidade das reacçõesPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Leão, Helena; Antunes, ElisaA velocidade das reações químicas e a lei da velocidade de uma reação. A equação de Arrhenius e sua confirmação experimental. Através de animação gráfica simulam-se colisões entre moléculas.
- Viscosity measurements of liquid toluene at low temperatures using a dual vibrating-wire techniquePublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Mata, José L. Correia da; Fareleira, João M. N. A.; Wakeham, William A.A recently developed dual vibrating-wire technique has been used to perform viscosity measurements of liquid toluene in the temperature range 213 K ≤ T ≤ 298 K, and at pressures up to approximately 20 MPa. The results were obtained by operating the vibrating-wire sensor in both forced and free decay modes. The estimated precision of the viscosity measurements, in either mode of operation, is ±0.5%, for temperatures above or equal to 273 K, increasing with decreasing temperature up to ±1% at 213 K. The corresponding overall uncertainty is estimated to be within ±1% and ±1.5%, respectively.
- Viscosity measurements of diisodecyl phthalate using a vibrating wire Instrument operated In free decay mode: comparison with results obtained with the forced mode of operationPublication . Oliveira, Carla Padrel de; Caetano, Fernando J. P.; Fareleira, João M. N. A.; Wakeham, William A.Recently, several authors described measurements of liquid viscosities higher than 100 mPa · s, using the vibrating wire technique in the forced oscillation mode of operation. The use of a vibrating wire instrument to measure increasingly higher viscosities poses experimental difficulties due to the consequent decrease of the quality factor of the resonance. This problem affects both modes of operation: in the steady-state, forced oscillation mode, there is a loss of definition of the resonance curve, and in the transient, free decay mode, there is an increase of the decrement of the sinusoidal time response of the vibrating wire. In the present work, we have measured the viscosity of diisodecyl phthalate (DIDP) at 0.1 MPa with a vibrating wire of nominal radius of 190 μm using the free decay mode of operation. The measurements covered a range of viscosities from (64 to 265) mPa · s. The results agreed with those we have obtained with a vibrating wire instrument operated in the forced mode and with the literature data, within the estimated experimental uncertainty (k ) 2) of ( 2 %. The comparisons indicate that the use of the free decay mode of operation does not necessarily imply a significant increase of uncertainty of the viscosity results at moderately high viscosities.
- Viscosity measurements of compressed liquid refrigerant blend R-507A, using a vibrating-wire techniquePublication . Avelino, Helena Maria da Nóbrega Teixeira; Fareleira, João M. N. A.; Oliveira, Carla Padrel deThe refrigerant blend R-507A (50 wt % HFC-143a, 50 wt % HFC-125) is an azeotropic mixture of hydrofluorocarbon refrigerants, 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125). The paper reports viscosity measurements, performed with a vibrating-wire viscometer, of the refrigerant blend R-507A,at five temperatures in the range (253 to 293) K. The measurements were carried out at pressures from slightly above saturation up to 10 MPa, except for the isotherms at 253.26 K where the maximum pressure was 7.52 MPa and at 263.23 K where the maximum pressure was 7.09 MPa. The overall uncertainty of these measurements is estimated to be ( 1.0 %. The data obtained were correlated by means of a modified hard-sphere based correlation technique. The root-mean-square deviation, rmsd, of the experimental results from the correlation equations is 0.23 %, and their bias is not significant. This correlation method has also been used to interpolate and extrapolate the present results to enable comparisons with measurements performed by other authors of the viscosity of liquid R-507A at different temperatures and pressures.
- Viscosity of Compressed Liquid 1,1,1-Trifluoroethane (HFC-143a) and Pentafluoroethane (HFC-125)Publication . Avelino, Helena Maria da Nóbrega Teixeira; Fareleira, João M. N. A.; Oliveira, Carla Padrel deThe viscosity of compressed liquid 1,1,1-trifluoroethane (HFC-143a) and pentafluoroethane (HFC-125) has been measured with a vibrating-wire viscometer at five temperatures between (254 and 293) K. The measurements were performed at pressures from above saturation up to 10 MPa, although for the isotherms at about 254 K the maximum pressure was approximately 5 MPa for HFC-143a and 7.4 MPa for HFC-125. For the isotherm at about 263 K, the highest pressure for HFC-143a was of the order of 7.5 MPa. The overall uncertainty of these results has been estimated to be less than ( 1.0 %. The measurements have been correlated using a scheme based on a hard-spheres model. The root mean square deviation of the experimental results from the correlations for HFC-143a and HFC-125 is ( 0.24 % and ( 0.25 %, respectively. The correlation scheme has been used to perform the small extrapolations of the present data to the saturation line to enable comparison with literature results at saturation pressure.