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Solids suspension in viscous Newtonian and non-Newtonian liquids

Al-Dhahir, Louis; (1991) Solids suspension in viscous Newtonian and non-Newtonian liquids. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Mechanically agitated solid mixing has been investigated for many years. A multitude of empirical correlations and theoretical models have been proposed in order to predict the minimum impeller speed, Njs, required for complete solids suspension. Hitherto, nearly all this research has focussed on low viscosity Newtonian liquids, typically water. This study has been concerned with extending the acquisition of solids suspension data into the transition and laminar regimes using both high viscosity Newtonian liquids as well as non-Newtonian as well as non-Newtonian liquids. The Newtonian liquids were mixtures of glycerol and water or corn syrup and water. Their viscosities varied from 0.022 to 11.35 Pas. The non-Newtonian liquids were made of aqueous solutions of Carbonyl Methyl Cellulose. These v/ere found to conform to a simple power-law rheology. The flow index, n, varied from 0.95 to 0.73, and the consistency index from 0.012 to 0.700. Suspension speed experiments were carried out in unbaffled, flat-bottomed tanks. Agitation was provided by a range of 45° pitch, six-bladed turbine impellers. Baffles, when used were found to hinder suspension. Solids distribution experiments were carried out in fully profiled vessels. A non-intrusive optical technique was used to sample local solids concentrations. By using such viscous liquids, it was found possible to suspend solids well within the laminar regime. Under such circumstances, those empirical and theoretical relationships derrived from turbulent conditions proved unsatisfactory for ether a prediction of Njs or an explaination of the solids suspension mechanism. Instead, an attempt has been made to explain the suspension mechanism, and hence to predict Njs using the mean liquid velocities found at close proximity to particles at the base of an agitated vessel. The Newtonian and non-Newtonian liquids were found to have markedly different axial solids concentration profiles both form each other and as compared with water.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Solids suspension in viscous Newtonian and non-Newtonian liquids
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/10122131
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