Influência da faixa de taxas de deformação na precisão de caracterizações reológicas de fluidos
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Data
2012-10-26
Autores
Capelli, Andrea [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Muitos trabalhos acadêmicos vêm sendo realizados atualmente a respeito da caracterização reológica de diversos fluidos. O problema é que os reômetros comerciais apresentam, em muitos casos, imprecisões, que se relacionam a diversos fatores, como os ligados às próprias condições de fluxo durante as análises. A escolha da faixa de taxas de deformação em que devem ser realizadas as análises é fundamental para a obtenção de resultados mais precisos. Neste trabalho realizou-se a caracterização reológica, em diferentes temperaturas, do diesel B, mistura de diesel (95 %) com biodiesel (5 %) que é distribuída em postos de combustíveis em todo o território brasileiro. Todas as análises reológicas foram realizadas em um reômetro rotacional AR-G2, marca TA Instruments, utilizando-se geometria de cilindros concêntricos. Verificou-se e descartou-se a influência do tempo sobre o comportamento reológico do fluido. Diferentes faixas de taxas de deformação foram testadas e fluidos de calibração foram utilizados para validar a escolha da melhor faixa de taxas de deformação. Determinaram-se curvas de escoamento e de viscosidade, e diferentes modelos reológicos – Newton, Ostwald de Waele, Bingham e Herschel-Bulkley –foram testados, buscando o melhor ajuste aos dados experimentais. As análises realizadas com os fluidos de calibração mostraram que o reômetro apresentava-se apropriado para a caracterização reológica de fluidos Newtonianos, especialmente em faixa de taxas de deformação entre 10 s -1 e 500 s -1 , para fluidos com viscosidade de ordem 10 -1 Pa.s a 1 Pa.s. A viscosidade da água foi verificada a 25 ºC e estava de acordo com a literatura, quando verificada em faixa de taxas de deformação entre 10 s -1 e 100 s -1 . O diesel B foi mais bem caracterizado reologicamente em faixa de taxas de deformação entre 10 s -1 e 500 s -1 , tendo apresentado...
Many academic studies have currently been conducted regarding the rheological characterization of several fluids. The problem is that commercial rheometers, in many cases, have inaccuracies that are associated to different factors such as those related to flow conditions during analysis. The choice of the range of strain rates in which the analysis must be performed is essential in order to obtain more accurate results. In this work the rheological characterization of diesel B, mixture of diesel (95%) and biodiesel (5%), which is distributed at gas stations throughout the Brazilian territory, was performed at different temperatures. All rheological analyzes were performed on an AR-G2 TA Instruments rotational rheometer, using concentric cylinder geometry. The time influence on the rheological behavior of the fluid was checked and discarded. Different ranges of strain rates were tested and calibration fluids were used to validate the choice of the best range of strain rates. Flow curves and viscosity were determined, and different rheological models – Newton, Ostwald of Waele, Bingham and Herschel-Bulkley – were tested, seeking the best fit to the experimental data. The analyzes performed with the calibration fluids showed that the rheometer was suitable for the rheological characterization of Newtonian fluids, especially in the range of strain rates between 10 s -1 and 500 s -1 for fluids with a viscosity of the order 10 -1 Pa.s a 1 Pa.s. The water viscosity was checked at 25 ° C and it was in agreement with the literature, when seen in the range of strain rates between 10 s -1 and 100 s -1 . Diesel B was better characterized rheologically in range of strain rates between 10 s -1 and 500 s -1 , and presented Newtonian behavior at all tested temperatures. The temperature influence on the rheological parameters obtained for diesel B was assessed between 10ºC and 40ºC... (Complete abstract click electronic access below)
Many academic studies have currently been conducted regarding the rheological characterization of several fluids. The problem is that commercial rheometers, in many cases, have inaccuracies that are associated to different factors such as those related to flow conditions during analysis. The choice of the range of strain rates in which the analysis must be performed is essential in order to obtain more accurate results. In this work the rheological characterization of diesel B, mixture of diesel (95%) and biodiesel (5%), which is distributed at gas stations throughout the Brazilian territory, was performed at different temperatures. All rheological analyzes were performed on an AR-G2 TA Instruments rotational rheometer, using concentric cylinder geometry. The time influence on the rheological behavior of the fluid was checked and discarded. Different ranges of strain rates were tested and calibration fluids were used to validate the choice of the best range of strain rates. Flow curves and viscosity were determined, and different rheological models – Newton, Ostwald of Waele, Bingham and Herschel-Bulkley – were tested, seeking the best fit to the experimental data. The analyzes performed with the calibration fluids showed that the rheometer was suitable for the rheological characterization of Newtonian fluids, especially in the range of strain rates between 10 s -1 and 500 s -1 for fluids with a viscosity of the order 10 -1 Pa.s a 1 Pa.s. The water viscosity was checked at 25 ° C and it was in agreement with the literature, when seen in the range of strain rates between 10 s -1 and 100 s -1 . Diesel B was better characterized rheologically in range of strain rates between 10 s -1 and 500 s -1 , and presented Newtonian behavior at all tested temperatures. The temperature influence on the rheological parameters obtained for diesel B was assessed between 10ºC and 40ºC... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Reologia, Biocombustíveis, Biodiesel, Viscosidade, Rheology
Como citar
CAPELLI, Andrea. Influência da faixa de taxas de deformação na precisão de caracterizações reológicas de fluidos. 2012. 89 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Biociências, Letras e Ciências Exatas, 2012.