臺灣博碩士論文加值系統

當質子交換膜燃料電池(PEMFC)的進料氫氣與進料氧氣發生反應，而產生電力時，在陰極會有水的產生。當水蒸氣開始累積達過飽和時會凝結成液態水。然而液態水會阻礙氣體進料的擴散，進而導致反應速率降低且電池性能也降低。我們使用不同的單電池參數來觀察氣體與液態水間的分佈情況。
本研究建立了一個穩態、二維方向、兩相多成分的質子交換膜燃料電池單電池模型，我們假設陰陽兩極觸媒層為一無厚度的反應界面，模型包括陰極擴散層、質子交換膜與陽極擴散層。
此模型中使用了Stefan-Maxwell方程式來描述多成分氣相擴散、液態水毛細管輸送現象、表面電化學動力學與膜相的控制方程式。為了處理兩相流問題，特別使用一類相平衡函數來處理氣液平衡，因此不用考慮擴散層的內部水前沿位置。在計算部分，進行了一系列參數的測試，包含陰陽兩極壓力差的影響，操作參數的影響( 電池操作溫度和進料溼度)。利用此模型觀察氣體、液態水分佈情況和液態水的前沿位置與電池性能的關係。經過一些參數的測試計算結果可看出，儘管本模型使用簡單的二維微分方程式，但是能夠發現質子交換膜燃料電池的基本特徵，所有涉及的參數具有一個精確的物理意義。因此，本模型可以用來描述一個質量傳輸和動力學性質的系統，用來測定質子交換膜燃料電池是可行的。

This study establishes a steady-state, two-dimensional, two-phase, multi- component proton exchange membrane fuel cell model. We assume that the anode and cathode catalyst layers are reaction interfaces without thickness. The model includes a cathode diffusion layer, a proton exchange membrane and anode diffusion layer. This model uses the Stefan-Maxwell equations to describe the multicomponent vapor diffusion, liquid water capillary transport phenomenon, surface electrochemical kinetics , and membrane phase transport equation. To handle two-phase flow problem, we use a phase equilibrium function to handle the gas-liquid equilibrium, without the need to determine the position of liquid water front in the diffusion layer.
In the study, we evaluate the operating parameters, including anode and cathode pressure difference, cell temperature and feed humidities. Computational results reveal that the present equations are able to uncover the essential features of PEMFCs in spite of their algebraic simplicity. Since the derived algebraic formulations are originated from a set of mechanistic two dimensional differential equations, all the involved parameters are endowed with a precise physical significance. The present model can be used to characterize the mass transport and kinetic properties in a systematic way so that in situ characterization of PEMFC is possible.

中文摘要 I
Abstract II
Table of content III
List of Figure V
List of Table VIII
Chapter 1 Introduction 1
1-1 Forward 1
1-2 Research motivation 1
Chapter 2 Literature review 3
2-1 Proton exchange membrane fuel cell structure 3
2-2 The Maxwell-Stefan equations for multicomponent diffusion in gases at low density 5
2-3 Capillary pressure 5
2-4 The water transport at membrane 7
2-5 COMSOL Multiphysics simulation program 8
2-5-1 Model building 8
2-5-2 Set of equations, formulated parameters, and the constants 9
2-5-3 The mesh setting, solving and post-processing 10
Chapter 3 Mathematical Formulations 12
3-1 Governing equations 13
3-1-1 Flux expressions and phase equilibrium approximation in the cathode and anode gas diffusion layers 13
3-1-2 Mass conservation in the cathode gas diffusion layer 14
3-1-3 Mass conservation in the anode gas diffusion layer 17
3-1-4 Proton exchange membrane 19
3-2 Boundary conditions 21
Chapter 4 Results and Discussion 30
4-1 The effect of pressure on the cell performance 30
4-1-1 Effect of pressure difference 30
4-1-2 Effect of symmetric imposed pressure 37
4-2 The influence of thickness of membrane 43
4-3 The influence of operating temperature on the cell performance 49
4-4 The influence of relative humidities on the cell performance 53
4-4-1 Cathode relative humidity effect 53
4-4-2 Anode relative humidity effect 59
Chapter 5 Conclusion 65
Reference 66
List of symbols 68

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