重組式甲醇燃料電池蒸發器沸騰熱傳研究

Boiling Heat Transfer study in the Micro-Evaporator of a Reformed Methanol Fuel Cell (RMFC)

張雅婷(Ya-Ting Chang)

指導教授 ： 潘欽

國立清華大學/原子科學院/工程與系統科學系/碩士(2017年)

摘要

本研究設計一應用於重組式甲醇燃料電池的微型蒸發器，旨在提供重組器穩定且氣化完全的燃料來源。為了解決一般重組器會遇到甲醇蒸氣與氧氣混合不均勻之問題，本研究事先將過氧化氫與甲醇進行混合，並探討其混合比例在微型蒸發器產生的沸騰熱傳現象，藉由調整過氧化氫與甲醇混合比例達到參數最佳化。
本微型蒸發器整體大小為2 cm 2 cm，採用前方1/3長度V型結構，提供均勻的流量分佈，並結合漸擴角度0.55°之漸擴流道，後段2/3局部加熱進行測試，比較四種不同工作流體的沸騰現象，分別為99.9%甲醇溶液與三種過氧化氫與甲醇體積比值C為1/2、1/3、1/4的混合溶液，並在0.18 ml/min、0.36 ml/min、0.54 ml/min三種流量下探討流量效應對熱傳性質的影響。
研究結果顯示，隨著流量增加，熱傳遞係數、臨界熱通率、熱傳效率，皆會增加，流量0.54 ml/min時，濃度C=1/3有最高熱傳效率69.1%與熱傳係數2048 W/m2K，其中臨界熱通率增益比例與流量成正比。添加過氧化氫能提升甲醇臨界熱通率，流量0.36 ml/min時臨界熱通率增益達最佳化，濃度C=1/2混合溶液相較於純甲醇溶液，臨界熱通率增益達138%，濃度C=1/2的混合溶液在流量0.54 ml/min時有最高的臨界熱通率196.3 kW/m2。因過氧化氫在高溫時會自行分解出氧氣，在濃度C=1/2的混合溶液，流量0.36 ml/min的情況下，其在加熱功率8W-14W出現週期性壁溫與出入口壓差震盪，雙相不穩定現象嚴重。
關鍵字:蒸發器、過氧化氫、甲醇、微流道、雙相流、重組式甲醇燃料電池

關鍵字

蒸發器 ； 過氧化氫 ； 甲醇 ； 微流道 ； 雙相流 ； 重組式甲醇燃料電池

並列摘要

The study investigates the boiling heat transfer and two-phase flow phenomena in a micro-evaporator with local heating for the diverging microchannels only. The micro-evaporator with a dimension of 2cm 2cm is composed of V-shaped micro diffusers for the entrance region to provide uniform flow distribution and parallel diverging channels with diverging angle of 0.55 degrees and 2/3 of the total length. In order to provide uniform mixture of methanol vapor, water vapor and oxygen to the reformer, the present study mixes the 50% hydrogen peroxide and methanol as the working fluid in the micro-evaporator. In the experiment, we compared the boiling heat transfer phenomenon of methanol and three mixtures of 50% hydrogen peroxide and methanol with volume ratio(C) of 1/2, 1/3, 1/4 with three flow rate, 0.18ml/min, 0.36ml/min, and 0.54ml/min.
The experimental results indicate that the addition of hydrogen peroxide can significantly enhance boiling heat transfer as well as the critical heat flux. In the case of C=1/2 and flow rate of 0.54ml/min, the critical heat flux is 196.3 kW/m2. With the increase of the flow rate, critical heat flux, heat transfer coefficient and heat transfer efficiency are promoted. The addition of hydrogen peroxide may also result in severe two phase flow boiling instability, i.e., pressure drop and wall temperature oscillations occurs: this is most severe for the case of C=1/2 and flow rate of 0.36ml/min. Based on the results of this study, the mixture with C=1/3 showing the best heat transfer coefficient may be the optimized working fluid for a micro-evaporator to serve the purpose of this study.

Key words: Hydrogen Peroxide、Evaporator、Microchannel、Two-Phase Flow、Reformed Methanol Fuel Cell

並列關鍵字

Hydrogen Peroxide ； Evaporator ； Microchannel ； Two-phase Flow ； Reformed Methanol Fuel Cell

參考文獻

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