金屬儲氫罐熱傳增強設計與實驗分析

Design and Experimental Analysis of Heat Transfer Enhancement for Hydride Storage Canisters

楊書聞(Shu-Wen Yang)

指導教授 ： 鍾志昂

國立中央大學/工學院/能源工程研究所/碩士(2011年)

摘要

本文使用LaNi5儲氫合金進行儲氫罐之吸放氫實驗，利用中空圓柱型儲氫罐探討儲氫罐於吸放氫之熱流特性，並於了解其特性後，針對其缺失設計另一添加熱管與內鰭片之熱傳增強儲氫罐以進行改良，最後再比較兩種儲氫罐吸放氫之性能，了解熱傳效率對於儲氫罐應用上之影響。
　　LaNi5由於合金吸氫為放熱反應，因此由中空圓柱型儲氫罐的吸氫實驗，可發現在只有水浴環境的情況下，受到儲氫合金熱阻影響，罐體中心並無良好的散熱能力，使得吸氫反應是由罐體表面往中心移動；而供氫壓力越大、環境溫度越低，皆會造成供氫壓力與吸氫平衡壓有較大之壓差，能縮短吸氫時的反應時間。放氫時，LaNi5合金為吸熱反應，在僅能依靠水浴環境藉由罐體表面傳遞熱能予儲氫合金的情況下，亦可發現放氫反應是由罐體表面向中心移動。若限制放氫體積流率，則環境溫度越高，維持設定之體積流率時間越長；若不限制體積流率，則溫度越高其放氫速率會越快，且溫度越高可釋放的氫氣量也越多。
　　使用熱傳增強儲氫罐，可在吸放氫時藉由鰭片與熱管增強罐體中心的合金與外界進行熱交換，讓吸放氫方向可由內而外與由外而內同時進行，吸氫速率相較於中空圓柱型儲氫罐增加三倍，合金最高溫度降低了20°C。而放氫速率相較於中空圓柱型儲氫罐提升44%的效能，合金最低溫度約提高10°C。顯示此熱傳增強儲氫罐有效的改善罐體中心熱傳不佳的問題。

關鍵字

LaNi5 ； 儲氫罐 ； 金屬氫化物 ； 氫氣

並列摘要

This thesis presents an experimental study of the impact of heat transfer on the performance of hydrogen absorption and desorption processes using LaNi5 hydrogen storage alloy. A hollow cylindrical storage tank and a cylindrical tank with a heat pipe and internal fins were designed and made to test the hydrogen storage characteristics and to demonstrate the storage efficiency improved by the heat transfer application.
　　Results from the experiments showed that when LaNi5 absorbed hydrogen, heat was released by the exothermic reaction. The rising temperature in turn raised the metal’s equilibrium pressure for hydrogen absorption and reduced the pressure difference from the hydrogen supply. Accordingly the hydriding reaction slowed down. Therefore, the greater the supply pressure of hydrogen and lower the ambient temperature of water bath, the quicker hydrogen could be charged into the hollow cylindrical tank. On the other hand, when the metal hydride desorbed hydrogen, heat was taken by the endothermic reaction. The descending temperature in turn reduces the metal’s equilibrium pressure for hydrogen desorption and reduced the pressure difference to the back pressure. The dehydriding reaction then slowed down as a result. Therefore, the higher the ambient temperature, the quicker hydrogen could be discharged from the storage tank. The above results indicated that enhancing heat transfer between the metal powders and the surrounding water bath should improve the performance of the storage tank.
　　To this end, a pilot design of hydrogen storage tank was made with a heat pipe and internal fins to increase the heat transfer rate. The heat pipe facilitated heat exchange between the central region of tank and the ambient water bath. The internal fins increased the effective conductivity of the metal bed. Experiments showed that hydrogen reactions occurred more evenly in the fined tanked than in the bare cylindrical tank. Accordingly, hydrogen uptake reached three times quicker and the alloy maximum temperature reduced as much as 20°C in the hydriding case, and hydrogen release rate was 44% quicker and the lowest temperature was increased by about 10°C in the dehydriding case for the heat transfer enhanced design. This thesis demonstrates that heat transfer enhancement could effectively improve the performance of hydrogen storage tank and may serve as a reference for the design of hydrogen storage tanks based on metal hydrides.

並列關鍵字

Hydrogen ； Metal Hydride ； hydrogen storage canister ； LaNi5

參考文獻

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