Topic
Velocity gradient
About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.
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TL;DR: The sedimentation velocity of a long-chain molecule is greatly increased by the hydrodynamic interaction of its constituent parts as discussed by the authors, which explains the experimental fact that various substances conform to Staudinger's viscosity rule and their sedimentation constant is dependent on molecular weight.
Abstract: The sedimentation velocity of a long-chain molecule is greatly increased by the hydrodynamic interaction of its constituent parts. If Kuhn's model of randomly kinked molecules is accepted, the application of a formula obtained by Burgers leads to an expression for the sedimentation velocity which is shown to account for experimental results mentioned in the literature.
This hydrodynamic interaction manifests itself in a way-which illustrates the hydrodynamic meaning of the “undurchspulte Knauel” assumed by Kuhn and makes his assumption very acceptable. It is emphasized, however, that this interaction is much less effective in the presence of a velocity gradient. This explains the experimental fact that various substances conform to Staudinger's viscosity rule, while at the same time their sedimentation constant is dependent on molecular weight.
20 citations
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TL;DR: Nonequilibrium molecular-dynamics simulations are used to study the shear-thinning behavior of immiscible symmetric polymer blends, which correlates more closely with a decrease in the component of the radius of gyration along the velocity gradient than with elongation along the flow.
Abstract: Nonequilibrium molecular-dynamics simulations are used to study the shear-thinning behavior of immiscible symmetric polymer blends. The phase-separated polymers are subjected to a simple shear flow imposed by moving a wall parallel to the fluid-fluid interface. The viscosity begins to shear thin at much lower rates in the bulk than at the interface. The entire shear-rate dependence of the interfacial viscosity is consistent with a shorter effective chain length s(*) that also describes the width of the interface. This s(*) is independent of chain length N and is a function only of the degree of immiscibility of the two polymers. Changes in polymer conformation are studied as a function of position and shear rate. Shear thinning correlates more closely with a decrease in the component of the radius of gyration along the velocity gradient than with elongation along the flow. At the interface, this contraction of chains is independent of N and consistent with the bulk behavior for chains of length s(*). The distribution of conformational changes along chains is also studied. Central regions begin to stretch at a shear rate that decreases with increasing N, while shear induced changes at the ends of chains are independent of N.
20 citations
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TL;DR: Low turbidity water is produced when fluid shear is kept at a minimum and use of the product Gθ for design of laminar flow tube flocculators is insufficient if residual turbidity is used as the metric for performance.
20 citations
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TL;DR: In this paper, a numerical model for turbulent opposed-jet mixing flows is developed with a one-dimensional (1-D) formulation with various turbulence models, and the distribution of mechanical-to-scalar time scale ratio, C D, is deduced from results obtained with a Reynolds stress model.
20 citations
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TL;DR: In this article, the three-dimensional moving grid and Improved Delayed Detached Eddy Simulation Shear-Stress Transport model which is a hybrid RANS/LES model were used to predict evolution processes of streamlines and velocity change in small rotary engine.
20 citations