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Abstract
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Computational Fluid Dynamics (CFD) uses advanced numerical models to predict flow, mixing and (bio)-chemical reactions. In drinking water engineering, CFD is increasingly applied to predict the performance of treatment installations and to optimise these installations. A lack of understanding of the hydraulics in drinking water treatment systems has resulted in suboptimal design of installations. The formation of unwanted disinfection-by-products and the energy consumption or use of chemicals is therefore higher than necessary.
The aim of this work is to better understand the hydraulic and (bio)-chemical processes in drinking water treatment installations using experimental and numerical techniques. By combining these techniques, CFD modelling is further developed as a tool to evaluate the performance of these installations. This leads to new insights in the applicability of models in ozone and UV systems, and new insights in design concepts of these systems. CFD modelling proves to be a powerful tool to understand the hydrodynamic and (bio)-chemical processes in drinking water systems. If applied properly, accounting for the complex turbulent motions and validated by experiments, this tool leads to a better design of UV reactors, ozone systems and other systems dictated by hydraulics.
Table of Contents
| Section Title | Page | Action | Price |
|---|---|---|---|
| Cover page | 1 | ||
| Half title page | 2 | ||
| Title page | 3 | ||
| Copyright page | 4 | ||
| Contents | 5 | ||
| Acknowledgements | 9 | ||
| Abstract | 10 | ||
| Chapter 1 | 12 | ||
| 1.1 HYDRAULICS IN DRINKING WATER ENGINEERING | 12 | ||
| 1.2 DISINFECTION AND OXIDATION TREATMENT | 14 | ||
| 1.2.1 Ozone systems | 14 | ||
| 1.2.2 UV systems | 15 | ||
| 1.3 HYDRAULIC PROCESSES | 16 | ||
| 1.4 CFD MODELLING | 17 | ||
| 1.4.1 The need for experiments | 18 | ||
| 1.5 AIM AND OUTLINE OF THIS THESIS | 18 | ||
| Chapter 2 | 21 | ||
| 2.1 INTRODUCTION | 21 | ||
| 2.2 FLOW MODEL | 22 | ||
| 2.3 TRACER TRANSPORT | 24 | ||
| 2.4 PHYSICAL OR CHEMICAL PROCESSES | 24 | ||
| 2.4.1 Ozone decay model | 24 | ||
| 2.4.2 UV irradiance model | 25 | ||
| 2.4.3 CT value or UV dose | 26 | ||
| 2.5 EFFECTS ON WATER QUALITY | 27 | ||
| 2.5.1 Disinfection model | 27 | ||
| 2.5.2 Advanced oxidation model | 29 | ||
| 2.6 ALTERNATIVE DISINFECTION MODELS FOR OZONE SYSTEMS | 31 | ||
| 2.6.1 Maximum disinfection capacity | 32 | ||
| 2.6.2 CSTR method | 32 | ||
| 2.6.3 CT10 method | 33 | ||
| 2.6.4 Segregated flow analysis (SFA) method | 33 | ||
| 2.6.5 Micro-mixing analysis (MMA) method | 34 | ||
| 2.7 UV PARAMETER STUDY | 34 | ||
| 2.7.1 Scale factor mean dose | 34 | ||
| 2.7.2 Optimal distance from the lamp to the outer wall | 36 | ||
| 2.7.3 Approximation of dose distribution | 36 | ||
| Chapter 3 | 39 | ||
| 3.1 INTRODUCTION | 39 | ||
| 3.2 STOCHASTIC DIFFERENTIAL EQUATIONS | 40 | ||
| 3.2.1 Brownian motion | 40 | ||
| 3.2.2 Itô vs Stratonovitch | 40 | ||
| 3.2.3 Fokker-Planck equation | 41 | ||
| 3.2.4 Fickian diffusion process | 41 | ||
| 3.2.5 Advection-diffusion process | 42 | ||
| 3.3 NUMERICAL IMPLEMENTATION ADVECTION | 43 | ||
| 3.3.1 Euler scheme | 43 | ||
| 3.3.2 Runge-Kutta scheme | 43 | ||
| 3.3.3 Semi-analytical scheme | 44 | ||
| 3.3.4 Time step requirements | 45 | ||
| 3.3.5 Test case: rotating flow | 46 | ||
| 3.4 NUMERICAL IMPLEMENTATION DIFFUSION | 46 | ||
| 3.4.1 Test case: wall treatment | 47 | ||
| 3.4.2 Test case: diffusion properties | 49 | ||
| 3.5 TEST CASE: CHANNEL FLOW | 49 | ||
| 3.6 NUMBER OF PARTICLES | 52 | ||
| Chapter 4 | 53 | ||
| 4.1 INTRODUCTION | 53 | ||
| 4.2 EXPERIMENTS OF LEIDUIN OZONE CONTACTOR | 55 | ||
| 4.2.1 Setup | 55 | ||
| 4.2.2 Residence time distributions | 56 | ||
| 4.3 CFD MODELLING OF VARIOUS OZONE CONTACTORS | 56 | ||
| 4.3.1 Modelling conditions | 56 | ||
| 4.3.2 RTD: Eulerian versus Lagrangian | 56 | ||
| 4.3.3 Validation of residence time distributions | 57 | ||
| 4.3.4 Mesh independency | 58 | ||
| 4.4 CFD RESULTS OF HYDRAULIC OPTIMISATIONS | 58 | ||
| 4.5 ASSESSMENT OF DISINFECTION MODELS | 63 | ||
| 4.6 SENSITIVITY TO KINETIC PARAMETERS | 65 | ||
| 4.7 SHORT-CIRCUITING | 67 | ||
| 4.7.1 Quick scan | 68 | ||
| 4.8 CONCLUSIONS | 69 | ||
| Chapter 5 | 70 | ||
| 5.1 INTRODUCTION | 70 | ||
| 5.2 EXPERIMENTS OF VARIOUS UV LAMP SHAPES | 72 | ||
| 5.2.1 Setup | 72 | ||
| 5.2.2 Results of flow measurements | 74 | ||
| 5.2.3 Discussion | 79 | ||
| 5.3 CFD MODELLING OF THE REFERENCE CYLINDER | 80 | ||
| 5.3.1 Modelling conditions | 80 | ||
| 5.3.2 Validation of velocity profiles | 80 | ||
| 5.4 COMPARISON BETWEEN LES MODEL AND K-ε MODEL | 83 | ||
| 5.4.1 Configurations | 83 | ||
| 5.4.2 Modelling approach | 84 | ||
| 5.4.3 Velocity fields | 85 | ||
| 5.4.4 Residence time distributions | 88 | ||
| 5.4.5 Dose distributions and disinfection | 89 | ||
| 5.4.6 Oxidation | 90 | ||
| 5.4.7 Discussion | 92 | ||
| 5.5 CONCLUSIONS | 93 | ||
| Chapter 6 | 96 | ||
| 6.1 INTRODUCTION | 96 | ||
| 6.2 EXPERIMENTS OF A BENCH-SCALE UV REACTOR | 97 | ||
| 6.2.1 Setup | 97 | ||
| 6.2.2 Residence time distributions | 100 | ||
| 6.2.3 Dye measurements | 102 | ||
| 6.2.4 Flow fields | 104 | ||
| 6.2.5 Lagrangian actinometry | 107 | ||
| 6.2.6 Disinfection | 108 | ||
| 6.2.7 Oxidation | 109 | ||
| 6.2.8 Discussion on the experimental results | 111 | ||
| 6.3 CFD MODELLING OF A BENCH-SCALE UV REACTOR | 111 | ||
| 6.3.1 Modelling conditions | 111 | ||
| 6.3.2 Mesh independency | 111 | ||
| 6.3.3 Validation | 113 | ||
| 6.4 DESIGN OF HYDRAULICALLY OPTIMISED UV REACTORS | 118 | ||
| 6.4.1 Overview of UV reactor designs | 118 | ||
| 6.4.2 UV dose distributions | 121 | ||
| 6.4.3 Results of energy consumption | 125 | ||
| 6.4.4 Design considerations | 128 | ||
| 6.5 CONCLUSIONS | 129 | ||
| Chapter 7 | 130 | ||
| 7.1 CFD MODELLING ASPECTS | 130 | ||
| 7.1.1 Turbulence modelling | 132 | ||
| 7.1.2 Lagrangian versus Eulerian | 132 | ||
| 7.1.3 Validation techniques | 133 | ||
| 7.1.4 Use of CFD models in the water industry | 134 | ||
| 7.2 SYSTEM DESIGN CONSIDERATIONS | 134 | ||
| 7.2.1 Ozone systems | 136 | ||
| 7.2.2 UV systems | 136 | ||
| 7.3 OUTLOOK FOR CFD MODELLING IN DISINFECTION/OXIDATION PROCESSES | 138 | ||
| References | 140 | ||
| Appendix A | 146 | ||
| STANDARD K-ε MODEL | 146 | ||
| LARGE-EDDY SIMULATION | 147 | ||
| Appendix B | 148 | ||
| CALCULATION METHOD | 148 | ||
| INTEGRATION OF UV IRRADIANCE OVER PARTICLE PATH | 149 | ||
| CONVERGENCE NUMBER OF SEGMENTS | 150 | ||
| List of publications | 151 | ||
| JOURNAL PUBLICATIONS (peer reviewed) | 151 | ||
| CONFERENCE PROCEEDINGS | 151 | ||
| NATIONAL PUBLICATIONS | 152 | ||
| DATA PUBLICATIONS | 152 | ||
| List of symbols | 153 | ||
| Roman symbols | 153 | ||
| Greek symbols | 154 | ||
| Abbreviations | 155 |