Experimental investigations of shear-induced particle migrations in concentrated suspensions undergoing shear.
Item
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Title
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Experimental investigations of shear-induced particle migrations in concentrated suspensions undergoing shear.
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Identifier
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AAI9908373
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identifier
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9908373
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Creator
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Tripathi, Anubhav.
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Contributor
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Adviser: Andreas Acrivos
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical
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Abstract
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This thesis describes the results of four sets of experiments which were performed to investigate shear-induced particle migrations in concentrated suspensions undergoing shear. The first part deals with the measurement of the shear-induced particle and fluid-tracer diffusivities in concentrated suspensions by a new correlation technique. These self-diffusivities were measured in the velocity gradient and vorticity directions in a narrow gap Couette device for values of the strain {dollar}\gamma\Delta t{dollar} ranging from 0.05 to 0.5, where {dollar}\gamma{dollar} is the applied shear rate and {dollar}\Delta t{dollar} is the correlation time. The particle diffusivities were found to be in good agreement with the experimental results of Leighton & Acrivos (1987a) and of Phan & Leighton (1993), even though these earlier studies were performed at much larger values of {dollar}\gamma\Delta t.{dollar} The second part of the thesis deals with the phenomenon of viscous resuspension in bidensity suspensions. Experiments were performed in a narrow gap Couette device using a bidensity suspension consisting of two type of particles, both having same size, one of which was heavy while the other had the same density as that of the suspending fluid. The resuspension height of an initially settled bed of heavy particles was measured over a ten-fold range of the applied shear rate using an imaging technique which was developed to study the particle migration process in concentrated bidisperse suspensions. It was found that, at a given shear rate, the resuspension height of the heavy particles increased with an increase in the concentration of the neutrally buoyant spheres. A bidensity model based on the Leighton & Acrivos migration theory was then developed and was found to be in good agreement with the experimental results. The third part of the thesis concerns a theoretical and experimental study for examining the maximum value of the volumetric feed rate possible in an inclined settler operated continuously in the bottom feeding mode. A new upper bound for the maximum value of the volumetric feed rate which can be tolerated under a given set of conditions was found theoretically as well as experimentally. Finally, in the last chapter, particle velocity and velocity fluctuations were measured in a concentrated suspension being sheared in a Couette device using laser Doppler anemometry. The purpose of these measurements was to provide information about values of the so-called suspension temperature T which equals the sum of the translational velocity fluctuations for a particle relative to its mean translational velocity. All the measurements were corrected for the influence of the LDA noise. (Abstract shortened by UMI.).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
