1 Introduction 1
1.1 Adhesive Particle Flow 1
1.2 Example Systems 2
1.3 Collision and Agglomeration of Particles in Turbulence 4
1.4 Migration of Microparticles in an Electrostatic Field 6
1.5 Deposition of Microparticles and Clogging Phenomenon 9
1.6 Discrete Element Methods for Adhesive Particles 12
1.7 A Road Map to Chaps. 2–6 13
References 14
2 A Fast Discrete Element Method for Adhesive Particles 17
2.1 Introduction 17
2.2 Discrete Element Method for Adhesive Particles 18
2.3 Critical Sticking Velocity for Two Colliding Particles 20
2.3.1 Temporal Evolution of the Collision Process 22
2.3.2 Prediction of the Critical Sticking Velocity 25
2.3.3 Effect of Particle Size 29
2.4 A Fast Adhesive DEM 31
2.4.1 Accelerating Adhesive DEM Using Reduced Stiffness 31
2.4.2 Modi ed Models for Rolling and Sliding Resistances 34
2.5 Determination of Parameters in Adhesive DEM 36
2.5.1 An Inversion Procedure to Set Parameters in Adhesive DEM 36
2.5.2 Comparison Between Experimental and DEM Results 39
2.6 Test on Packing Problem 40
2.6.1 Packing Fraction and Coordination Number 43
2.6.2 Local Structure of Packings 45
2.6.3 Interparticle Overlaps and Normal Forces 46
2.7 Summary 48
References 49
3 Agglomeration of Microparticles in Homogenous Isotropic Turbulence 51
3.1 Introduction 51
3.2 Methods 52
3.2.1 Fluid Phase Calculation 52
3.2.2 Equation of Motion for Solid Particles 53
3.2.3 Multiple-time Step Framework 54
3.2.4 Simulation Conditions 55
3.2.5 Identi cation of Collision， Rebound and Breakage Events 57
3.2.6 Smoluchowski’s Theory 59
3.3 Collision Rate， Agglomerate Size and Structure 60
3.4 Effect of Stokes Number 62
3.5 Exponential Scaling of Early-Stage Agglomerate Size 62
3.6 Agglomeration Kernel and Population Balance Modelling 64
3.7 Effect of Adhesion on Agglomeration 65
3.8 Effect of Adhesion on Breakage of Agglomerates 68
3.9 Formulation of the Breakage Rate 68
3.10 Agglomerate Size Dependence of the Breakage Rate 76
3.11 Role of Flow Structure 76
3.12 Conclusions 78
References 79
4 Migration of Cloud of Low-Reynolds-Number Particles with Coulombic and Hydrodynamic Interactions 81
4.1 Introduction 81
4.2 Formulation of Problem 81
4.3 Effect of Coulomb Repulsion on Cloud Shape 84
4.3.1 Cloud Shape 84
4.3.2 Effect of Fluid Inertia 87
4.3.3 Stability of the Cloud 88
4.4 Evolution of Particle Cloud Under Strong Repulsion 91
4.4.1 Scaling Analysis and Continuum Description 91
4.4.2 Prediction of Cloud Size and Migrating Velocity 93
4.4.3 Discussion 97
4.5 Summary 98
References 99
5 Deposition of Microparticles with Coulomb Repulsion 101
5.1 Introduction 101
5.2 Models and Methods 102
5.2.1 Simulation Conditions 102
5.2.2 Forces on Particles 103
5.2.3 Average-Field Calculation for Coulomb Interactions
in 2D Periodic System 103
5.3 Effects of Coulomb Interaction on Packing Structure 106
5.4 Scaling Analysis of the Interparticle Force 109
5.5 Governing Parameters for the Packing Structure 112
5.6 Phase Diagram 115
5.7 Summary 117
References 118
6 Deposition of Charged Micro-Particles on Fibers: Clogging Problem 119
6.1 Introduction 119
6.2 Models and Method 120
6.2.1 Simulation Conditions: Two Fiber System 120
6.2.2 Gas Phase Simulation 121
6.2.3 Solid-Phase: Discrete-Element Method (DEM) 122
6.2.4 Governing Parameters 123
6.3 Clogging/Non-clogging Transition 124
6.4 Measurement of Particle Capture Ef ciency 127
6.4.1 Repulsion Effect: The Critical State 128
6.4.2 Structure Effect 130
6.5 Summary 133
References 134
7 Conclusions and Perspective 135
7.1 Conclusions 135
7.2 Future Work 137
References 138
內容試閱：
Adhesive particle ?ow arises in many applications in industry， nature， and life sciences and has driven great research interests in areas of aerosol ?ltration， dust mitigation， nanoparticle deposition， ceramics manufacturing， fouling of MEMS devices， sediment transport， and production of fuel cells. An in-depth understanding of the relationship between microscopic interparticle interactions and the collective behavior of a large number of particles would be helpful to understand and further design large-scale devices. However， linking the microscopic properties of discrete particles to the macroscopic behaviors of particle ?ow systems is never a simple task. The dif?culty lies in the complicated interacting modes between particles， namely the electrostatic interaction， the hydrodynamic interaction， and the contact interactions， across several orders of magnitude in time and length scales.
Within the past few decades， the discrete element method (DEM)， in which the motion， collision， and adhesion of individual particles are resolved in time and space， has been developed to model particle collective dynamics from single- particle level. DEM coupled with computational ?uid dynamics (i.e.， CFD-DEM) has shown powerful capabilities in investigating particle-laden ?ows. Moreover， there has recently been rapid progress on understanding the physics related to the intermolec- ular and surface forces， which enable us to develop more rational adhesive contact models. Scalable and ef?cient computational frameworks have also been proposed for handling long-range many-body interactions and for collision resolution. It is recognized that merging the expertise across various disciplines of ?uid and solid mechanics， condensed matter physics， materials science， and applied mathematics will signi?cantly improve our understanding of particle dynamics in electrostatic and ?ow ?elds.
The objective of this thesis is to propose new approaches for modeling contacting interactions and electrostatic interactions between microparticles in the framework of discrete element methods and to present an insightful view on the agglomeration， migration， and deposition of microparticles in electrostatic and ?ow ?elds. The ?rst chapter discusses various applications of adhesive particle ?ows. Chapter 2 starts with a simple case of binary collisions of adhesive particles to show how the discrete element method gives the information on the force， the displacement， and the energy conversion. A novel fast DEM based on the reduced particle Young’s modulus is then proposed to accelerate the computation. In Chap. 3， the fast DEM is coupled with direct numerical simulation to investigate the agglomeration of particles in homoge- neous isotropic turbulence. The structure and the size distribution of agglomerates are obtained. The agglomeration and collision-induced breakage rates are formu- lated based on the classic theory for particle collisions in turbulence. In Chap. 4， the evolution of spherical clouds of charged particles that migrate in a uniform external electrostatic ?eld is then investigated by Oseen dynamics and a continuum approach， and the scaling laws for evolution of cloud radius and particle number density are derived. Finally， in Chaps. 5 and 6， an elaborate investigation of the deposition of charged particles on a ?at plane and ?bers is presented. The ?ndings， together with previous results for neutral particles， form a more complete picture of ?ltration and deposition of microparticles.
I believe that the results in this book will substantially impact the ?eld relevant to adhesive particle ?ows. Beyond that， the ?ndings here may also have broader implications for granular ?uidization， liquid–solid suspensions， and colloidal gels， where complicated particle–particle interactions exist.
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