臺灣博碩士論文加值系統

本研究針對重組式甲醇燃料電池 (RMFC) ，設計一矽質叉流式微流道熱交換器，以有效地利用重組器 (reformer) 產出的廢熱，一方面降低重組器產生出來的氫氣溫度，另一方面將此熱量傳給液態甲醇，使其蒸發以利重組反應進行。
根據上述構想，實驗使用的叉流式微流道熱交換器採用微機電 (MEMS) 體型加工技術製作，材料以單晶矽晶圓為基材，其具有良好的導熱能力。其中微流道熱交換器晶片大小為2×2 cm2，且在其上下面蝕刻深度為200μm冷熱端流場板，再與pyrex 7740玻璃做陽極接合 (anodic bonding)。根據實驗室多年來的研究結果顯示，漸擴截面積的微流道設計可以降低液體在沸騰過程中出現的不穩定現象，因此本研究透過漸擴矩形微流道的設計來製作冷側(甲醇端)的流道，而熱側(氦氣端)則是採用均勻截面積矩形微流道。
根據甲醇重組器的操作條件，系統需要達到約200℃以上的高溫才能由甲醇轉化為氫氣，且重組反應為放熱反應，所以產生的氫氣於出口處可能會達到250℃以上的高溫。因此，本實驗設定進入微熱交換器之氦氣(替代氫氣)高溫至250-300℃。藉由改變熱測的溫度，來探討不同流動方向配置在微流道熱交換器所產生的熱交換效率差異及單相與雙相沸騰熱傳。實驗並利用高速攝影機，觀察流體沸騰時流道的雙相流譜。
綜觀研究成果發現，叉流式微流道熱交換器之效率在甲醇沸騰時隨熱側熱功率的增加而逐漸上升。此外，效率也隨甲醇質量通率的增加而增加，且此流量效應在單相時較為顯著。本研究之微流道熱交換器的效率最高約可達0.91且移熱能力約為50 kWm-2 。

To utilize the exhausted heat produced from a methanol reformer (a part of a reformed methanol fuel cell) effectively, the development of a highly effective microchannel heat exchanger (MCHE) is of critical importance. This design could not only reduce the temperature of the hydrogen released from a reformer but also transfer the heat to the liquid methanol. Following our previous researches on the co- and counter-flow MCHEs, the two-phase flow boiling heat transfer characteristics in a cross-flow MCHE is investigated in the present work. The MCHE is made from 4-inches silicon wafer prepared through microfabrication processes with a dimension of 20 mm × 20 mm. Eighteen microchannels are etched on each side, and covered with Pyrex 7740 glass by anodic bonding. The channel depth on both cold- and hot-side is 200 μm, and the thickness of the wall between is the same of 200μm. To make the boiling flow more stable, the microchannels in the cold side employ a diverging design, as suggested in our previous studies. Liquid methanol is used as the boiling fluid, while hot helium gas is employed to simulate hydrogen.
From the experiment results, it indicates that in the efficiency with methanol boiling in the cold side gradually increases with an increase in hot-side thermal power. Moreover, the efficiency increases significantly with an increase in the mass flux. The highest efficiency could achieve about 0.91 and the transferred cooling power is around 50 kWm-2.

目錄
摘要 i
Abstract ii
致謝 iii
目錄 iv
表目錄 vii
圖目錄 viii
符號說明 xi
第一章 緒論 1
1.1前言 1
1.2研究動機與目的 3
1.3研究方法 4
1.4論文架構 5
第二章 文獻回顧 6
2.1熱交換器相關研究 6
2.2微流道內之流動沸騰相關研究 10
2.3非均勻熱通率加熱流道相關研究 12
第三章 微流道熱交換器製作與實驗系統 14
3.1微流道熱交換器製作 14
3.1.1微機電製程基本原理 14
3.1.2微流道熱交換器製程 16
3.1.3測試段製程 20
3.2實驗系統 23
3.2.1實驗設備環路 23
3.2.2高效能層析幫浦 24
3.2.3 數據擷取系統與溫度及差壓之量測 25
3.2.4影像擷取系統 25
3.2.5實驗步驟 26
3.2.6 實驗誤差分析 28
第四章 微流道熱交換器理論分析 29
4.1能量平衡與熱傳分析計算 29
4.1.1 甲醇水溶液沒有像變化的分析 29
4.1.2 甲醇水溶液發生沸騰後的分析 32
4.2單相熱傳遞係數分析計算 32
4.3雙相熱傳遞係數分析計算 36
4.4甲醇出口乾度 39
4.5熱效率分析 39
第五章 實驗結果與討論 40
5.1微熱交換器內冷側微流道之雙相流動型態 40
5.2微流道熱交換器之沸騰熱傳實驗分析 49
5.2.1微流道熱交換器之進出口平均溫度 49
5.2.2 冷側進/出口溫度特性 53
5.2.3 沸騰曲線 55
5.2.4 冷側熱傳遞係數 57
5.2.5 甲醇出口乾度對冷側熱傳遞係數的效應 60
5.3 效率 62
第六章 結論與建議 64
6.1本論文研究成果 64
6.2未來研究建議 65
參考文獻 66

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