Mesoscale Modeling and CFD Simulation of Gas-fluidized Bed w
发布时间：2021-11-13 13:25
气固鼓泡床反应器在能源、化工等领域均有重要应用,如烯烃聚合,煤/生物质燃烧,矿石焙烧等。气固流态化中往往呈现颗粒聚团或气泡等介尺度结构,且实际应用中颗粒通常具有多分散性（涉及不同颗粒尺寸或密度）,这使得介尺度结构的形成机制更加复杂。这种多分散性还会导致床内出现颗粒分层等现象,在低速的密相床中尤为显著,影响了相间动量传递和反应行为。深入理解多分散流态化中的颗粒分离和混合现象对于合理设计反应器以及确定最佳的操作条件至关重要。近年来,随着多相流理论和计算流体力学（CFD）技术的迅速发展,特别是介尺度理论的兴起,使得CFD成为研究多相复杂流动行为的强大工具。在各种模拟方法中,连续介质模型（又称为欧拉模型）由于其较少的计算量被广泛用于工程计算。而在模拟气固流动时,曳力系数对于准确捕捉气固流动中的介尺度结构等典型特征起到关键作用。很多研究者指出,在低速多分散密相床（如鼓泡床）中曳力是影响不同颗粒分离和混合的关键因素。在过去的十几年中,以能量最小多尺度模型（EMMS）为代表的介尺度模型被成功应用于气固流化床反应器的模拟,但是绝大部分的研究都基于均一颗粒的流态化系统（或称单分散流态化系统）。由于单分散...
【文章来源】：中国科学院大学(中国科学院过程工程研究所)北京市
【文章页数】：132 页
【学位级别】：博士
【文章目录】：
摘要
ABSTRACT
CHAPTER 1 INTRODUCTION
1.1 LITERATURE REVIEW
1.2 TYPICAL CHALLENGES IN LOW-VELOCITY FLUIDIZATION
1.2.1 Heterogeneous structures
1.2.2 Characteristics of bubbles
1.2.3 Bubble size
1.2.4 Bubble velocity
1.2.5 Fluidization of binary particles
1.3 MODELING APPROACHES
1.3.1 Direct Numerical Simulation
1.3.2 Discrete Particle Method
1.3.3 Multi-fluid model
1.3.4 Governing equations
1.3.5 Drag force
1.4 OBJECTIVES AND OUTLINE
CHAPTER 2 NUMERICAL EXPERIMENT ON GAS-SOLID FLUIDIZATION
2.1 INTRODUCTION
2.2 SIMULATIONS OF A PERIODIC DOMAIN
2.2.1 Simulation settings
2.2.2 Results and discussions
2.2.3 Solid velocity distribution in different local position
2.2.4 Effects of pressure drop on solid velocity distribution
2.3 EXPERIMENTAL DATA FOR THE SIMULATION OF A BUBBLING FLUIDIZED BED
2.3.1 Simulation settings
2.3.2 Results and discussions
2.4 SUMMARY
CHAPTER 3 PARAMETER ANALYSIS OF EMMS/BUBBLING MODEL FOR MONODISPERSE SYSTEM
3.1 INTRODUCTION
3.2 EMMS/BUBBLING MODEL FOR MONODISPERSE SYSTEM
3.2.1 Multi-scale description
3.2.2 Hydrodynamic equations
3.3 EFFECTS OF BUBBLE SIZE
3.3.1 Different bubble size correlations
3.3.2 Effects of bubble size correlation on structural parameters
3.3.3 Effects of bubble size correlation on H_d
3.4 DISCUSSION ON STRUCTURAL PARAMETERS
3.4.1 The volume fraction of dense phase and the dense phase voidage
3.4.2 Gas velocities in dense and dilute phases
3.4.3 Acceleration term
3.4.4 Variation of Nst with voidage
3.5 SUMMARY
CHAPTER 4 EXTENDING THE EMMS/BUBBLING MODEL TO THE BINARY MIXTURE:FORMULATION AND STEADY-STATE VALIDATION
4.1 INTRODUCTION
4.2 EMMS/BINARY BUBBLING MODEL
4.2.1 Multiscale resolution
4.2.2 Hydrodynamic equations for steady state
4.2.3 Numerical Method
4.3 MODEL VALIDATION FOR STEADY STATE
4.3.1 Validation for monodisperse system
4.3.2 Validation for binary particle system
4.4 SUMMARY
CHAPTER 5 EMMS/ BINARY DRAG MODEL AND PARAMETER ANALYSIS
5.1 INTRODUCTION
5.2 MODEL DESCRIPTION
5.2.1 Hydrodynamic equations for unsteady state:
5.2.2 Structure-dependent drag coefficient
5.2.3 Solution scheme
5.3 PARAMETER ANALYSIS
5.3.1 The model input parameters
5.3.2 Sensitivity analysis
5.3.3 Effects of the assumption of particles inside bubbles
5.3.4 Effects of the assumption for equal accelerations
5.4 SUMMARY
CHAPTER 6 VALIDATION OF THE EMMS/BINARY DRAG MODEL
6.1 INTRODUCTION
6.2 EXPERIMENTAL DESCRIPTION
6.2.1 The case of size segregation
6.2.2 The case of combined size and density segregation
6.3 MATHEMATICAL MODEL
6.3.1 Conservation equations
6.3.2 Constitutive relations
6.3.3 The KTGF-based solid stress
6.3.4 The gas-solid drag force
6.3.5 The solid-solid drag force
6.3.6 The determination of maximum packing Limit
6.4 SIMULATION SETTINGS
6.5 RESULTS AND DISCUSSION
6.5.1 Simulation of Case 1
6.5.2 Voidage distribution
6.5.3 Solid concentration for flotsam and jetsam
6.5.4 Solid velocity
6.5.5 Axial profile of jetsam
6.5.6 Simulation of Case 2
6.5.7 Voidage distribution
6.5.8 Solid concentration for flotsam and jetsam
6.5.9 Solid velocity
6.5.10 Axial profile of jetsam
6.6 SUMMARY
CHAPTER 7 CONCLUSIONS AND PROSPECTS
LIST OF ABBREVIATIONS
REFERENCES
CURRICULUM VITAE
ACKNOWLEDGEMENT
本文编号：3493101
【文章来源】：中国科学院大学(中国科学院过程工程研究所)北京市
【文章页数】：132 页
【学位级别】：博士
【文章目录】：
摘要
ABSTRACT
CHAPTER 1 INTRODUCTION
1.1 LITERATURE REVIEW
1.2 TYPICAL CHALLENGES IN LOW-VELOCITY FLUIDIZATION
1.2.1 Heterogeneous structures
1.2.2 Characteristics of bubbles
1.2.3 Bubble size
1.2.4 Bubble velocity
1.2.5 Fluidization of binary particles
1.3 MODELING APPROACHES
1.3.1 Direct Numerical Simulation
1.3.2 Discrete Particle Method
1.3.3 Multi-fluid model
1.3.4 Governing equations
1.3.5 Drag force
1.4 OBJECTIVES AND OUTLINE
CHAPTER 2 NUMERICAL EXPERIMENT ON GAS-SOLID FLUIDIZATION
2.1 INTRODUCTION
2.2 SIMULATIONS OF A PERIODIC DOMAIN
2.2.1 Simulation settings
2.2.2 Results and discussions
2.2.3 Solid velocity distribution in different local position
2.2.4 Effects of pressure drop on solid velocity distribution
2.3 EXPERIMENTAL DATA FOR THE SIMULATION OF A BUBBLING FLUIDIZED BED
2.3.1 Simulation settings
2.3.2 Results and discussions
2.4 SUMMARY
CHAPTER 3 PARAMETER ANALYSIS OF EMMS/BUBBLING MODEL FOR MONODISPERSE SYSTEM
3.1 INTRODUCTION
3.2 EMMS/BUBBLING MODEL FOR MONODISPERSE SYSTEM
3.2.1 Multi-scale description
3.2.2 Hydrodynamic equations
3.3 EFFECTS OF BUBBLE SIZE
3.3.1 Different bubble size correlations
3.3.2 Effects of bubble size correlation on structural parameters
3.3.3 Effects of bubble size correlation on H_d
3.4 DISCUSSION ON STRUCTURAL PARAMETERS
3.4.1 The volume fraction of dense phase and the dense phase voidage
3.4.2 Gas velocities in dense and dilute phases
3.4.3 Acceleration term
3.4.4 Variation of Nst with voidage
3.5 SUMMARY
CHAPTER 4 EXTENDING THE EMMS/BUBBLING MODEL TO THE BINARY MIXTURE:FORMULATION AND STEADY-STATE VALIDATION
4.1 INTRODUCTION
4.2 EMMS/BINARY BUBBLING MODEL
4.2.1 Multiscale resolution
4.2.2 Hydrodynamic equations for steady state
4.2.3 Numerical Method
4.3 MODEL VALIDATION FOR STEADY STATE
4.3.1 Validation for monodisperse system
4.3.2 Validation for binary particle system
4.4 SUMMARY
CHAPTER 5 EMMS/ BINARY DRAG MODEL AND PARAMETER ANALYSIS
5.1 INTRODUCTION
5.2 MODEL DESCRIPTION
5.2.1 Hydrodynamic equations for unsteady state:
5.2.2 Structure-dependent drag coefficient
5.2.3 Solution scheme
5.3 PARAMETER ANALYSIS
5.3.1 The model input parameters
5.3.2 Sensitivity analysis
5.3.3 Effects of the assumption of particles inside bubbles
5.3.4 Effects of the assumption for equal accelerations
5.4 SUMMARY
CHAPTER 6 VALIDATION OF THE EMMS/BINARY DRAG MODEL
6.1 INTRODUCTION
6.2 EXPERIMENTAL DESCRIPTION
6.2.1 The case of size segregation
6.2.2 The case of combined size and density segregation
6.3 MATHEMATICAL MODEL
6.3.1 Conservation equations
6.3.2 Constitutive relations
6.3.3 The KTGF-based solid stress
6.3.4 The gas-solid drag force
6.3.5 The solid-solid drag force
6.3.6 The determination of maximum packing Limit
6.4 SIMULATION SETTINGS
6.5 RESULTS AND DISCUSSION
6.5.1 Simulation of Case 1
6.5.2 Voidage distribution
6.5.3 Solid concentration for flotsam and jetsam
6.5.4 Solid velocity
6.5.5 Axial profile of jetsam
6.5.6 Simulation of Case 2
6.5.7 Voidage distribution
6.5.8 Solid concentration for flotsam and jetsam
6.5.9 Solid velocity
6.5.10 Axial profile of jetsam
6.6 SUMMARY
CHAPTER 7 CONCLUSIONS AND PROSPECTS
LIST OF ABBREVIATIONS
REFERENCES
CURRICULUM VITAE
ACKNOWLEDGEMENT
本文编号：3493101
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