Abstract

The mixing quality of a solid-liquid stirred tank operating in the turbulent regime was investigated, numerically and to an extent experimentally. Simulations were performed by coupling Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). The results were evaluated against experimental data obtained using Electrical Resistance Tomography (ERT). This facilitated a novel and more rigorous assessment of CFD-DEM coupling – i.e. based on the spatial distribution of particle concentrations. Furthermore, a new mixing index definition was developed to quantify suspension quality to work in tandem with existing dispersion mixing indexes. This provides a more complete interpretation of mixing quality. In this work, it was found that the model underestimated suspension and dispersion due to model limitations associated with mesh size and fluid-particle interaction models. Furthermore, the predicted mixing quality was sensitive to changes in the drag model, including other fluid-particle interaction forces in simulations, and variations in certain particle properties

Highlights

  • A basic Electrical Resistance Tomography (ERT) measurement system is comprised of three components: the sensor interface, the data acquisition system (DAS), and the data processing software

  • The wear and damage resulting from particle-geometry contacts in hydraulic conveying systems has been the subject of a few Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) studies

  • By increasing the sliding and rolling friction coefficients, it was observed that the fraction of suspended particles increased, and steady-state was reached faster. These findings suggest that Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) coupling is the more appropriate modeling method – when compared to Two Fluid Method (TFM) – since it can more accurately account for the particle physics responsible for certain hydrodynamic behaviors observed in solid-liquid mixing systems

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Summary

A NOVEL APPROACH FOR ANALYZING MIXING QUALITY IN SOLID-LIQUID STIRRED TANKS VIA

Cindy Tran B.Eng in Chemical Engineering, Ryerson University, Toronto, Canada, 2015. AUTHOR'S DECLARATION FOR ELECTRONIC SUBMISSION OF A THESIS I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I authorize Ryerson University to lend this thesis to other institutions or individuals for the purpose of scholarly research. I further authorize Ryerson University to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. I understand that my thesis may be made electronically available to the public

Theoretical Principles of Electrical Resistance Tomography (ERT)
Sensor Interface
Data Acquisition System (DAS)
Image Reconstruction
ERT Applications in Solid-Liquid Mixing
Numerical Simulation Methods
Single-Phase Modeling
Lagrangian Models - Discrete Element Method (DEM)
Eulerian Models - Computational Fluid Dynamics (CFD)
Two-Phase Modeling
Theoretical
General Overview of Governing Equation Forms
Modeling of Fluid-Particle Interaction Forces
Coupling Approaches and Schemes
Simulation Software
Advantages and Disadvantages
CFD-DEM Applications
Fluidized Beds
Hydraulic Conveyance
Separation and Classification
Solid-Liquid Mixing
Research Objectives
ERT Measurement System
Quantification of Mixing Quality with Mixing Indexes
Experimental Results
Governing Equations for Liquid Phase
Governing Equations for Solid Phase
Solid-Liquid Interaction Force Models
Simulation Conditions and Settings
Fluid-Phase Mesh and Boundary Conditions used in CFD Solver
Mesh Quality in CFD-DEM coupling
Grid Independence Test in CFD
Particle Generation Procedure
Model Sensitivity Tests for Mixing Quality
Influence of Drag Models
Influence of Other Fluid-particle Interaction Forces
Influence of Particle Properties
Full Text
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