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Velocity and concentration fluctuations in concentrated solid-liquid flows Open Access


Other title
Solids concentration fluctuations
Solids velocity fluctuations
Solid-liquid flows
Electrical Impedance Tomography
Type of item
Degree grantor
University of Alberta
Author or creator
Hashemi, Seyed Abolreza
Supervisor and department
R. S. Sanders (Chemical and Materials Engineering)
Examining committee member and department
Brian Fleck (mechanical Engineering)
Jos Derksen (Chemical and Materials Engineering)
Anthony Yeung (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering
Chemical Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The aim of this research was to investigate experimentally the turbulent flow of concentrated slurries in horizontal pipelines and to improve the fundamental understanding of mechanism(s) that govern these. High speed Electrical Impedance Tomography (EIT) was combined with advanced signal processing techniques to develop a measurement procedure to obtain solids concentration distributions and turbulent intensity profiles in a highly concentrated solid-liquid mixture. Specific Energy Consumption (SEC), which is a measure of transport efficiency, was used to find the optimum operating condition for heterogeneous (settling) slurry flows. The effects of solids concentration, mixture velocity and particle diameter on SEC were determined using the equivalent-fluid and near-wall lift models for fine- and coarse-particle slurries, respectively. The analysis shows that the minimum SEC occurs at a solids concentration of approximately 30% by volume. Model predictions were compared with the results of numerous experimental studies. In spite of the utility of phenomenological models, such as the near-wall lift model, many fundamental questions in solid-liquid flows remain. Issues include the poor understanding of the mechanisms that govern these complex flows, and the lack of local parameters measured and available for model validation studies. Among the various parameters, solids and liquid concentration fluctuations and turbulent intensities are arguably the most important pieces of information that need to be measured. In horizontal slurry pipe flows, solids velocity and concentration fluctuations were measured for concentrated sand-water mixtures (20 - 35% solids by volume). Slurries of narrowly sized sand (d50 = 100 μm) were tested in a 52 mm (i.d.) pipe loop at different mixture velocities (2 - 5 m/s) that were significantly above the deposition velocity. The results showed that the magnitude of the local solids concentration fluctuations is greater near the pipe wall and increases as the mixture velocity increases. Additionally, the concentration fluctuations are greater near the pipe invert, particularly at lower mixture velocities and/or concentrations where the solids concentration profiles are asymmetric. Experiments were also carried out in a 10.16 cm (i.d.) solid-liquid fluidized bed using 2, 3 and 4 mm mono-sized spherical glass beads with water as the continuous phase. A reduced solids concentration in the central region of the bed, which is known to occur during the bubbly (aggregate) fluidization regime, was observed. This study provides further insight into the dynamic behaviour of liquid-solid fluidized beds through the measurement of local solids concentration fluctuations.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Hashemi, S. A., and R.S. Sanders, 2012. Study of the dynamic behaviour of a solid-liquid fluidized bed using high speed Electrical Impedance tomography, 8th International Conference on Multiphase Flow (ICMF), 26 – 31 May, Jeju, KoreaHashemi, S. A., A. Sadighian, I. Shah, and R.S. Sanders, 2012. Solids velocity and concentration fluctuations in concentrated liquid-solids pipe flows, 6th International Symposium on Process Tomography (ISPT), 26-28 March 2012, Cape Town, South Africa.Hashemi, S.A., R. S. Sanders and K.C. Wilson, 2010. Specific energy consumption and desirable operating condition for fine-particle slurries. Hydrotransport 18, 22 -24 September, Rio de Janeiro, Brazil.Hashemi, S.A. and R. S. Sanders, 2010. Concentration and velocity distribution in dense coarse-particle slurries. 7th International Conference on Multiphase Flow (ICMF), May 30 - June 4, Tampa, Florida, USA

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