臺灣博碩士論文加值系統

本研究係利用計算流體動力學的模型，計算三相流化床的流動力學。研究中，我們已試著計算三相流化床複雜的流動力學：床的伸展、兩相停滯、床的降壓、流化床的行為與速度數據圖表。這個模型的開發，是利用商業版的CFD code Fluent 6.2. 用來激發的阻力模型，則是用Gidaspow 模型。分析重點則在於高為1.5公尺，直徑0.1公尺的圓柱。Euler-Euler多階段流動方法，有能力預測氣體-液體-固體流化床的整體表現。結果顯示液體阻塞，隨著液體進入的速度增加而增加。氣體的阻塞，則是隨著氣體流率增加而增加，且隨著液體流動比率的增加而減少。

A computational fluid dynamics model used to understand the hydrodynamics of three phase fluidized bed is presented in this paper. In the present investigation, an attempt has been made to study the complex hydrodynamics of three phase fluidized bed; bed expansion, holdup of two phases, bed pressure drop, fluidized bed voidage and velocity profile. The model is developed by using the commercial CFD code Fluent 6.2. The drag model for simulating is used Gidaspow model. The main focus on for analyzing the results is on the column with 1.5m height and diameter 0.1m. Euler-Euler multiphase flow approach is capable of predicting the overall performance of gas-liquid-solid fluidzed bed. The results obtained show that the liquid holdup increased with the inlet liquid velocity, gas holdup increased with the flow rate of gas and decreased with an increase in the liquid flow rate.

Contents

Abstract ii
Acknowledgments iii
Contents iv
List of Tables vii
List of Figures viii
List of Symbols ix
Chapter1 Introduction 1
1.1 A brief introduction about gas–liquid–solid fluidized bed 1
1.2 Advantages of three phase fluidized bed 2
1.3 Disadvantages of fluidized bed 2
1.4 Application of three phase fluidized bed 3
1.5 Modes of operation of gas-liquid-solid fluidized bed and flow regimes 4
1.6 Variables affect the quality of fluidization 4
1.7 Complexion of three phase system 5
1.8 Objectives 6
1.9 Outline of the Thesis 6
Chapter 2 Literature Review 7
2.1 Experimental investigation 7
2.2 CFD modeling investigation 9
Chapter 3 CFD Modeling of Three Phase Fluidized Bed 11
3.1 Computational fluid dynamics (CFD) 11
3.2 Advantages of CFD 11
3.3 Application of CFD 12
3.4 Limitations of CFD 13
3.5 Discretization methods in CFD 13
3.5.1 Finite difference method (FDM) 14
3.5.2 Finite volume method (FVM) 14
3.5.3 Finite element method (FEM) 15
3.5.4 Comparison of three methods 15
3.6 CFD solution procedure 16
3.6.1 Pre-processor 17
3.6.2 Solver 19
3.6.3 Post-processing 21
3. 7 Approaches for numerical calculations of multiphase flow 22
3.7.1 Euler-Lagrange approach 23
3.7.2 Euler-Euler approach 23
3.7.2.1 Volume of fluid method (VOF) 24
3.7.2.2 Mixture model 25
3.7.2.3 The Euler model 25
3.8 Guidelines for multiphase models 25
3.9 Computational flow model 26
3.9.1 Conservation equations 27
3.9.2 Closure law for turbulence 28
3.9.3 Closure law for solid pressure 29
3.9.4 Closure law for inter-phase momentum exchange 30
3.9.4.1 Liquid-solid inter-phase drag force (FD,ls) 30
3.9.4.2 Gas-liquid inter-phase drag force (FD,gl) 30
3.9.4.3 Gas-solid inter-phase drag force (FD,gs) 30
Chapter 4 Numerical Methodology 33
4.1 Mesh created in GAMBIT 33
4.2 Selection of models for simulation 34
4.3 Boundary and initial conditions 35
4.4 Solution techniques 37
Chapter 5 Result and Discussion 40
5.1 Phase dynamics 41
5.2 Bed expansion 43
5.3 Liquid holdup 46
5.4 Gas holdup 50
5.5 Bed voidage 53
5.6 Pressure drop 55
5. 7 Change in velocity profile with simulation time 57
Chapter 6 Conclusion and future perspective of the work 62
6.1 Conclusions 62
6.2 Future perspective of the work 63
References 64

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