臺灣博碩士論文加值系統

本研究目的在使用有限元素分析法(FEA)分析平板式固態氧化物燃料電池(SOFC)使用雲母封裝材料在運作流程中之熱應力分佈。首先，利用電化學及熱傳分析產生含三層單元電池之SOFC電池堆在各個階段的溫度分佈圖，然後將這些獲得的溫度場輸入此三維三層電池堆的有限元素模型中，每個單元電池基本上都包含了電池板(PEN)、金屬連接板、鎳網、封裝玻璃陶瓷以及雲母封裝材料。在以往的研究中，雲母封裝材料的結構功能並未被考慮，因此，為了提供更接近實際情況的熱應力分析結果，本研究所建立之三層電池堆有限元素分析模型將包含雲母封裝材料，特別是將比較使用玻璃陶瓷與使用雲母封裝材料、不同裝配溫度以及雲母材料楊氏係數不同對電池堆熱應力分佈的影響。
分析結果顯示，不同的裝配溫度只對於在裝配後的熱應力分佈有影響。當裝配溫度從200上升到400 oC，隨著裝配溫度的上升，裝配後在室溫下的熱應力也伴隨上升，但對於運轉階段及停機狀態下的熱應力分佈影響不大。將雲母封裝材料的兩個不同楊氏係數輸入模型進行分析，發現改變雲母的楊氏係數只對於雲母封裝材料的熱應力有顯著影響，對於其他元件的熱應力分佈幾乎沒有影響。與先前全部使用玻璃陶瓷作為封裝材料之熱應力分佈比較，使用雲母封裝材料在裝配後及停機狀態，各元件之熱應力值比較小；但在運轉階段，則有相對較大的熱應力。而全部使用封裝玻璃設計的部分，在穩態工作狀態下有較低的熱應力值而在裝配後及停機狀態下的熱應力值較高。兩種不同封裝設計之熱應力值呈現相反的趨勢。

The aim of this study is, by using finite element analysis (FEA), to characterize the thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack with a compressive sealing design at various stages. The temperature profiles generated by an integrated thermo-electrochemical model were applied to calculate the thermal stress distributions in a multiple-cell SOFC stack by using a three-dimensional (3-D) FEA model. The constructed 3-D FEA model consists of the complete components used in a practical SOFC stack, including positive electrode-electrolyte-negative electrode (PEN) assembly, interconnect, nickel mesh, glass-ceramic seals, and compressive mica seals. Incorporation of the compressive mica sealant, which was never considered in previous studies, into the 3-D FEA model would produce more realistic results in thermal stress analysis and enhance the reliability of predicting potential failure locations in an SOFC stack. The stress fields at different assembly temperatures and the effect of anisotropic elastic moduli of mica sealant were investigated.
The thermal stresses in each component at room temperature after assembly were increased when the assembly temperature was increased form 200 oC to 300 and 400 oC. However, the assembly temperature did not affect the thermal stress distributions significantly at steady-operation and shutdown stages. Two different elastic moduli of mica material were used in the FEA model and the simulation results indicated that the critical stresses in each component at a specific stage were comparable except for the mica sealants. Thermal stress distributions obtained in the current study were also made a comparison with those in a rigid-bonding sealing design. The thermal stresses in each component were larger at the after-assembly and shutdown stages but lower in the operation condition for the rigid-bonding type of sealing design. That trend of stress distribution was opposite to that for a compressive sealing design used in the current study.

TABLE OF CONTENTS

LIST OF TABLES......IV
LIST OF FIGURES......V
1.INTRODUCTION.........................................1
1.1 Solid Oxide Fuel Cell.................1
1.2 Components of a SOFC..................3
1.2.1 Anode..........4
1.2.2 Cathode........5
1.2.3 Electrolyte....5
1.2.4 Interconnect...6
1.2.5 Sealant........7
1.3 Thermal Stresses in Planar SOFC.......9
1.4 Purpose and Scope....................11
2.MODELING.............................................13
2.1 Finite Element Model.................13
2.2 Material Properties..................14
2.3 Boundary and Constrained Conditions..16
2.4 Temperature Profiles.................16
2.5 Investigated Cases...................17
2.6 Failure Criteria.....................19
3.RESULTS AND DISCUSSION...............................21
3.1 Stress Fields at Different Assembly Temperatures ....................................21
3.2 Effect of Anisotropic Elastic Moduli of Mica
Sealant..............................25
3.3 Comparison of Thermal Stresses in Different
Sealing Designs......................26
4.CONCLUSIONS.........................................28
REFERENCES............................................30
TABLES................................................33
FIGURES...............................................37

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