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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: In this article, the authors derived the laws of viscosity and velocity gradient in the analysis of the flow of macromolecular solution in a tube and showed that the longest particle dimension rotates in a plane normal to the vortex axis and the effect of the aspect ratio of the suspended particles or molecules is also considered.
Abstract: The conception of viscosity as action per unit volume is used in the analysis of the flow of a suspension or macromolecular solution in a tube. The flow mechanism adduced involves the postulation of molecular vortices of which the suspended particles or molecules form the nuclei. This mechanism is used as a basis for the derivation of a relationship between the specific viscosity of the suspension and the linear dimensions of the vortices. The laws of Einstein, Staudinger, Huggins and their co-workers are derived simply and as special cases of this relationship. The law relating viscosity with concentration is also derived with reference to the same mechanism. This law assumes the form ηsp = an + bn2 where a and b are constants and ηsp and n are respectively the specific viscosity and molecular concentration of the solution. It is shown to be in good agreement with typical experimental results. The effect of the aspect ratio of the suspended particles or molecules is also considered and it is shown that the longest particle dimension rotates in a plane normal to the vortex axis. Although no quantitative relationship between viscosity and velocity gradient has been derived the mechanism is observed to lead to results in qualitative agreement with the experimental data.

18 citations

Journal ArticleDOI
TL;DR: In this article, the authors used an electrochemical method to measure the flow characteristics near the walls of baffled vessels equipped with a six-blade Rushton type turbine and found that the flow conditions near the wall could be described by a meridional profile of the friction coefficient, which depends on the Reynolds number, on the flow index of the power-law fluids and on the d/D simplex.
Abstract: Characteristics of flow near the walls of baffled vessels equipped with a six blade Rushton type turbine were measured by an electrochemical method. A directionally sensitive probe was used for determination of velocity gradient vector fields. It was found that the flow conditions near the wall could be described by a meridional profile of the friction coefficient. An extensive set of experimental data obtained by the limiting current technique showed that the profile depends on the Reynolds number, on the flow index of the (power-law) fluids and on the d/D simplex. The maximum values of the friction coefficient characterizing flow near the impeller plane can be correlated by a simple relation of the laminar boundary layer type.

18 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of two surrogate surfaces to directly measure gas dry deposition were explored using wind tunnel experiments and two-dimensional (2D) computational fluid dynamic (CFD) models.

18 citations

Journal ArticleDOI
TL;DR: It was shown that the aggregate size decreased with increasing global velocity gradient G and it was demonstrated that, with increasing G, the aggregates became more compact and regular (the D2 fractal dimension increased) and the suspension became more homogeneous in size.
Abstract: This paper describes the influence of the global velocity gradient G on the properties of aggregates formed during the coagulation/flocculation process. The methods of image and fractal analysis were used to determine aggregate size and structure, respectively. The influence of these aggregate properties on separation using depth filtration is also described. Experiments were conducted in a pilot plant operation. The suspension was formed in a flow mixing tank with global velocity gradients ranging from 28.4-307.2 s(-1) and ferric sulphate used as a coagulant. Filtration velocities were 3 and 6 m h(-1). Predictably, it was shown that the aggregate size decreased with increasing global velocity gradient G. Furthermore it was demonstrated that, with increasing G, the aggregates became more compact and regular (the D2 fractal dimension increased) and the suspension became more homogeneous in size. The aggregates with the smallest diameter and highest D2 fractal dimension displayed the best filterability, i.e. penetrated throughout the full depth of the filter bed and generated a minimum pressure drop.

18 citations

Journal ArticleDOI
TL;DR: In this article, general radiative transfer in spherical, differentially-moving media is considered and the character of the first two moment equations in the stationary case is investigated, and it is shown that moment equations form a hyperbolic system when the logarithmic velocity gradient is positive, provided that a reasonable condition on the Eddington factors is met.
Abstract: General--relativistic, frequency--dependent radiative transfer in spherical, differentially--moving media is considered. In particular we investigate the character of the differential operator defined by the first two moment equations in the stationary case. We prove that the moment equations form a hyperbolic system when the logarithmic velocity gradient is positive, provided that a reasonable condition on the Eddington factors is met. The operator, however, may become elliptic in accretion flows and, in general, when gravity is taken into account. Finally we show that, in an optically thick medium, one of the characteristics becomes infinite when the flow velocity equals $\pm c/\sqrt 3$. Both high--speed, stationary inflows and outflows may therefore contain regions which are ``causally'' disconnected.

18 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202318
202233
2021127
2020116
2019134
201892