Velocity and concentration fluctuations in concentrated solid-liquid flows

  • Author / Creator
    Hashemi, Seyed Abolreza
  • 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.

  • Subjects / Keywords
  • Graduation date
    Fall 2013
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.