Microparticle Dynamics in Electrostatic and Flow Fields

Description

This thesis proposes new approaches for modelling contacting interactions and electrostatic interactions between microparticles in the framework of the discrete element method and presents a systematic investigation on the agglomeration, migration and deposition of microparticles in presence of electrostatic and flow fields. It reports an exponential-form scaling for the size distribution of early-stage agglomerates in homogeneous isotropic turbulence and formulate the agglomeration and deagglomeration rates. The evolution of spherical clouds of charged particles that migrate under the action of an external electrostatic field is then investigated. Scaling laws of cloud radius and particle number density are obtained by solving a continuum convection equation. Finally, it investigates the deposition of charged particles on a flat plane and fibers. A dimensionless adhesion parameter is constructed to predict the structure of deposits. The temporal evolution of the deposit structure, particle capture efficiency, and the pressure drop are displayed with varying values of Coulomb repulsion and adhesion magnitudes.  Supervisor’s Foreword Acknowledgements Contents Nomenclature English Characters (Lowercase) English Characters (Uppercase) Greek Symbols Superscript Subscript 1 Introduction 1.1 Adhesive Particle Flow 1.2 Example Systems 1.3 Collision and Agglomeration of Particles in Turbulence 1.4 Migration of Microparticles in an Electrostatic Field 1.5 Deposition of Microparticles and Clogging Phenomenon 1.6 Discrete Element Methods for Adhesive Particles 1.7 A Road Map to Chaps. 2摥映數爠eflinkchap:222–6摥映數爠eflinkchap:666 References 2 A Fast Discrete Element Method for Adhesive Particles 2.1 Introduction 2.2 Discrete Element Method for Adhesive Particles 2.3 Critical Sticking Velocity for Two Colliding Particles 2.3.1 Temporal Evolution of the Collision Process 2.3.2 Prediction of the Critical Sticking Velocity 2.3.3 Effect of Particle Size 2.4 A Fast Adhesive DEM 2.4.1 Accelerating Adhesive DEM Using Reduced Stiffness 2.4.2 Modified Models for Rolling and Sliding Resistances 2.5 Determination of Parameters in Adhesive DEM 2.5.1 An Inversion Procedure to Set Parameters in Adhesive DEM 2.5.2 Comparison Between Experimental and DEM Results 2.6 Test on Packing Problem 2.6.1 Packing Fraction and Coordination Number 2.6.2 Local Structure of Packings 2.6.3 Interparticle Overlaps and Normal Forces 2.7 Summary References 3 Agglomeration of Microparticles in Homogenous Isotropic Turbulence 3.1 Introduction 3.2 Methods 3.2.1 Fluid Phase Calculation 3.2.2 Equation of Motion for Solid Particles 3.2.3 Multiple-time Step Framework 3.2.4 Simulation Conditions 3.2.5 Identification of Collision, Rebound and Breakage Events 3.2.6 Smoluchowski's Theory 3.3 Collision Rate, Agglomerate Size and Structure 3.4 Effect of Stokes Number 3.5 Exponential Scaling of Early-Stage Agglomerate Size 3.6 Agglomeration Kernel and Population Balance Modelling 3.7 Effect of Adhesion on Agglomeration 3.8 Effect of Adhesion on Breakage of Agglomerates 3.9 Formulation of the Breakage Rate 3.10 Agglomerate Size Dependence of the Breakage Rate 3.11 Role of Flow Structure 3.12 Conclusions References 4 Migration of Cloud of Low-Reynolds-Number Particles with Coulombic and Hydrodynamic Interactions 4.1 Introduction 4.2 Formulation of Problem 4.3 Effect of Coulomb Repulsion on Cloud Shape 4.3.1 Cloud Shape 4.3.2 Effect of Fluid Inertia 4.3.3 Stability of the Cloud 4.4 Evolution of Particle Cloud Under Strong Repulsion 4.4.1 Scaling Analysis and Continuum Description 4.4.2 Prediction of Cloud Size and Migrating Velocity 4.4.3 Discussion 4.5 Summary References 5 Deposition of Microparticles with Coulomb Repulsion 5.1 Introduction 5.2 Models and Methods 5.2.1 Simulation Conditions 5.2.2 Forces on Particles 5.2.3 Average-Field Calculation for Coulomb Interactions in 2D Periodic System 5.3 Effects of Coulomb Interaction on Packing Structure 5.4 Scaling Analysis of the Interparticle Force 5.5 Governing Parameters for the Packing Structure 5.6 Phase Diagram 5.7 Summary References 6 Deposition of Charged Micro-Particles on Fibers: Clogging Problem 6.1 Introduction 6.2 Models and Method 6.2.1 Simulation Conditions: Two Fiber System 6.2.2 Gas Phase Simulation 6.2.3 Solid-Phase: Discrete-Element Method (DEM) 6.2.4 Governing Parameters 6.3 Clogging/Non-clogging Transition 6.4 Measurement of Particle Capture Efficiency 6.4.1 Repulsion Effect: The Critical State 6.4.2 Structure Effect 6.5 Summary References 7 Conclusions and Perspective 7.1 Conclusions 7.2 Future Work References