Generic properties of rheological flow curves |
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| Affiliation: | 1. Department of Chemical Engineering, Facultad de Ciencias y Tecnologías Químicas, University of Castilla-La Mancha, Campus Universitario s/n, 13071, Ciudad Real, Spain;2. Department of Chemical Engineering, Instituto de Tecnologías Química y Medioambiental, University of Castilla-La Mancha, Campus Universitario s/n, 13071, Ciudad Real, Spain;3. Geoenvironmental Group, Civil Engineering School, University of Castilla-La Mancha, Avda. Camilo José Cela s/n, 13071, Ciudad Real, Spain;1. Departamento de Física Aplicada III, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain;2. Centro Nacional de Aceleradores (Universidad de Sevilla – CSIC – Junta de Andalucía), Avenida Tomas Alva Edison 7, 41092 Sevilla, Spain;1. Warsaw University of Life Sciences (SGGW), Faculty of Agriculture and Biology, Department of Botany, Nowoursynowska 159, Building 37, 02-776 Warsaw, Poland;2. University of Agriculture, Faculty of Biotechnology and Horticulture, Institute of Plant Biology and Biotechnology, Unit of Botany and Plant Physiology, Al. 29-Listopada 54, 31-425 Krakow, Poland;3. University of Agriculture, Faculty of Agriculture and Economics, Institute of Soil Science and Agrophysics, Department of Soil Science and Soil Protection, Al. Mickiewicza 21, 31-120 Krakow, Poland;4. University of Agriculture, Center for Technology Transfer, Al. Mickiewicza 21, 31-120 Krakow, Poland;1. Department of Reproduction and Artificial Insemination, Faculty of Veterinary Medicine, Cumhuriyet University, Sivas, Turkey;2. Department of Reproduction and Artificial Insemination, Faculty of Veterinary Medicine, Ondokuz Mayıs University, Samsun, Turkey;1. Dep. de Psicologia Bàsica, Clínica i Psicobiologia, Universitat Jaume I. Spain;2. Dep. de Matemàtiques. Institute of New Imaging Technologies, Universitat Jaume I, Spain;3. Dep. de Matemàtiques. Institute of Mathematics and Applications, Universitat Jaume I, Spain |
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| Abstract: | The interpretation and comparison of viscosity data for fluids in planar Couette flow are discussed using a generic rheological function, familiar from studies of polymeric liquids. The particular data are generated by non-equilibrium molecular dynamics (NEMD) simulations of model fluids, however the analysis has wider validity. The mathematical properties of the established flow curves are investigated and, inter alia, a consistent definition of the critical shear rate is established. It is also shown that the use of inappropriate, but commonly used, independent variables leads to curves whose qualitative behaviour is extremely sensitive to the physical parameters. Such a range of qualitative behaviour can lead to erroneous quantitative conclusions when interpreting physical (or model) data. A particular example is the assumption of a linear dependence of the viscosity on the square-root of the shear rate, as often used in the NEMD literature. The developed framework also enables the systematic comparison of simulations of the same molecular fluid performed at different state points. This is illustrated for the case of three recently published and apparently conflicting NEMD results for n-butane. |
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