臺灣博碩士論文加值系統

A one-dimensional, nonisothermal model of PEM fuel cell which describes mass, heat and electrochemical phenomena and takes into account the multiphase presence of water in the flow channels, was investigated. Sensitivity analysis was conducted with respect to eleven parameters whose value assignment seemed essential for best simulation results. The MATLAB subroutine sens_sys was used to obtain the absolute and relative sensitivities, and the parameters with significant influence on the model were identified. Model-based optimization was performed with the objective of maximizing the power density subject to constraints. Eight design variables, which have strong influence on the power density, were selected as the design/decision variables. The nature of the optimization problem was explored using the powerful graphical capability of MATLAB. Strong nonlinearity observed in the graphical solution encouraged the use of nonlinear programming as the optimization scheme to determine the best solution for selected process constraints. Optimization results, which were presented as function of average current density, showed high value of average power density and satisfaction of the imposed side and physical constraints suggesting that optimality and feasibility of the design have been achieved.

A one-dimensional, nonisothermal model of PEM fuel cell which describes mass, heat and electrochemical phenomena and takes into account the multiphase presence of water in the flow channels, was investigated. Sensitivity analysis was conducted with respect to eleven parameters whose value assignment seemed essential for best simulation results. The MATLAB subroutine sens_sys was used to obtain the absolute and relative sensitivities, and the parameters with significant influence on the model were identified. Model-based optimization was performed with the objective of maximizing the power density subject to constraints. Eight design variables, which have strong influence on the power density, were selected as the design/decision variables. The nature of the optimization problem was explored using the powerful graphical capability of MATLAB. Strong nonlinearity observed in the graphical solution encouraged the use of nonlinear programming as the optimization scheme to determine the best solution for selected process constraints. Optimization results, which were presented as function of average current density, showed high value of average power density and satisfaction of the imposed side and physical constraints suggesting that optimality and feasibility of the design have been achieved.

Table of Contents
ABSTRACT…………………………………………………………………………….…i
ACKNOWLEDGEMENTS……………………………………………………………..ii
TABLE OF CONTENTS……………………………………………………………….iii
LIST OF FIGURES ……………………………………………………………………vii
LIST OF TABLES…………………………………………………………..................xiv
CHAPTER 1 INTRODUCTION……………………………………………………….1
1.1 BRIEF HISTORY OF FUEL CELLS……………………………………………3
1.2 TYPES OF FUEL CELLS……………………………………………………….5
1.2.1 Polymer Electrolyte Membrane………………………………………....6
1.2.2 Phosphoric Acid…………………………………………………………7
1.2.3 Direct Methanol………………………………………………………….8
1.2.4 Alkaline………………………………………………………………….8
1.2.5 Molten Carbonate………………………………………………………..9
1.2.6 Solid Oxide……………………………………………………………..10
1.2.7 Regenerative (Reversible)……………………………………………...12
1.3 FUEL CELL PERFORMANCE………………………………………………...15
1.3.1 Basic Principles………………………………………………………...15
1.3.2 Electrochemistry of a Fuel Cell………………………………………...16
1.3.3 Ideal Performance of a Fuel Cell……………………………………….17
1.3.4 Actual Performance…………………………………………………….19
1.3.5 Cell Efficiency………………………………………………………….22
1.4 PEM FUEL CELL………………………………………………………………23
1.4.1 Physical Structure and Operating Principle of a PEMFC……………...24
1.5 WATER MANAGEMENT IN PEM FUEL CELL……………………………..26
1.6 THERMAL MANAGEMENT IN PEM FUEL CELL………………………….27
1.7 RESEARCH OBJECTIVE……………………………………………………...29
1.8 RESEARCH MOTIVATION…………………………………………………...31
1.9 THESIS OUTLINE……………………………………………………………..33
1.10 NOMENCLATURE…………………………………………………………...35
1.11 REFERENCES………………………………………………………………....36
CHAPTER 2 LITERATURE REVIEW………………………………………………37
2.1 STATE OF THE ART…………………………………………………………..37
2.2 SURVEY OF THE EXISTING PEM FUEL CELL LITERATURE…………...39
2.2.1 Flow Channels Modeling………………………………………………...39
2.2.2 Diffusion Layers Modeling………………………………………………40
2.2.3 Electrodes Modeling……………………………………………………...42
2.2.4 Membrane Modeling……………………………………………………..44
2.2.5 Electrochemical Modeling………………………………………………..46
2.2.6 Fuel Cell Body Modeling………………………………………………...50
2.2.7 Thermal Modeling………………………………………………………..51
2.2.8 Auxiliary Components Modeling………………………………………...53
2.2.9 Numerical Solution and Simulation……………………………………...55
2.2.10 Model Validation………………………………………………………..58
2.2.11 Parameter Estimation……………………………………………………59
2.2.12 Sensitivity Analysis……………………………………………………..61
2.2.13 Optimization…………………………………………………………….64
2.3 REFERENCES………………………………………………………………….78
CHAPTER 3 PEM FUEL CELL MODEL FORMULATION……………………...84
3.1 MODEL DESCRIPTION……………………………………………………….84
3.2 ASSUMPTIONS………………………………………………………………...86
3.3 FORMULATION OF THE GOVERNING EQUATIONS……………………..87
3.3.1 Mass Balance……………………………………………………………..87
3.3.2 Energy Balance…………………………………………………………...92
3.3.3 Cell Potential……………………………………………………………..93
3.4 NUMERICAL METHOD………………………………………………………97
3.5 NOMENCLATURE…………………………………………………………...105
3.6 REFERENCES………………………………………………………………...107
CHAPTER 4 PARAMETER SENSITIVITY……………………………………….109
4.1 SENSITIVITY ANALYSIS…………………………………………………...109
4.2 SENSITIVITY INDEX………………………………………………………..110
4.3 SENSITIVITY ANALYSIS USING MATLAB………………………………113
4.3.1 Description of ode15s Solver…………………………………………...113
4.3.2 Description of sens_ind and sen_sys Functions………………………...113
4.3.3 Use of sens_ind and sens_sys…………………………………………...114
4.4 SOLUTION APPROACH……………………………………………………..115
4.5 RESULTS AND DISCUSSIONS……………………………………………...116
4.5.1 Analysis Based on Absolute Sensitivity………………………………...116
4.5.2 Analysis Based on Relative Sensitivity…………………………………125
4.6 NOMENCLATURE………………………………………………………...…134
4.7 REFERENCES………………………………………………………………...135
CHAPTER 5 SYSTEM OPTIMIZATION……………………………………….….137
5.1 OPTIMIZATION PROBLEM………………………………………………....137
5.1.1 Selection of Design Variables…………………………………………..137
5.1.2 Objective Function…………………………………………………..….138
5.1.3 Constraint Equations.........................................................................…...140
5.1.4 Side Constraints…………………………………………………………141
5.1.5 Scaling of the Design Variables……………………………………..….141
5.2 OPTIMIZATION METHOD…………………………………………………..142
5.2.1 Investigation of the Nature of Solution by Graphical Technique…….…142
5.2.2 Nonlinear Programming……………………………………….………..143
5.2.3 Analytical Conditions…………………………………………………...146
5.2.4 Kuhn-Tucker Conditions………………………………………………..147
5.3 SOLUTION APPROACH………………………………………………..……149
5.4 RESULTS AND DISCUSSIONS……………………………………………...153
5.4.1 Nature of Solution………………………………………………………153
5.4.2 Nonlinear Programming………………………………………………...186
5.5 NOMENCLATURE…………………………………………………………...203
5.6 REFERENCES…………………………….…………………………………..205
CHAPTER 6 CONCLUSIONS AND FUTURE WORKS………………………….207
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