鑒於國際原油存量日漸耗竭，尋找替代能源實已刻不容緩。由於氫氣具有高能量密度以及環保的特性，因此它被評估為未來能源系統中最具有潛力能量載體之一，在安全性與成本的考量下，以金屬氫化物作為儲存方式是較為理想的；但其在儲存與運輸方面尚有許多問題需要克服。由於金屬氫化物儲氫系統的儲氫與釋氫是一伴隨著放熱與吸熱的可逆化學反應，因此系統內部的熱傳良好與否對整體儲氫系統的儲釋氫性能影響甚劇。本數值研究藉由添加發泡金屬來增強儲氫系統內部的熱傳，並以本研究團隊在先前研究中所建立的金屬氫化物 (LaNi5) 儲釋氫行為計算模型作為儲氫系統的理論熱質傳模型，且將計算結果與其他學者所發表的實驗數據進行驗證，進而探討系統參數設計對其性能之影響等重要研究課題。

在先前本研究團隊研究發現僅需很少的金屬發泡結構即可有效地增強系統內部熱傳效果，使儲氫時間大大的縮短。同時，在固定系統體積下，發泡金屬所添加的體積百分率 (φmf) 增加會占據系統內部空間而使儲氫金屬含量減少，最大可儲氫量降低。因此，在指定的儲氫量需求下，存在一最佳φmf值使得儲氫時間最短。然而，在先前所討論發泡金屬體積百分率 (φmf) 均是以均勻的方式分佈在系統內部。但由於系統內部位置距離冷卻壁面或加熱壁面位置的不同，其所需的熱傳重要性也會有所不同。因此，本論文討論重點為在固定總發泡金屬含量下，依其空間位置所需熱傳重要性不同，添加不同體積百分率的發泡金屬。透過此方式能使儲氫系統在其最大可儲氫量不變的情況下，進一步的提升系統性能。研究發現，此方式確能使系統在儲氫與釋氫的反應中能進一步縮短 33% 的儲釋時間和提升平均釋氫流率 33%。此外，在系統釋氫的穩定性上也有 22% 的增益。

關鍵字：金屬氫化物儲氫系統、熱傳增益、發泡金屬、儲氫量、發泡金屬分佈、儲氫時間、釋氫時間、釋氫流率、流率穩定性

In view of the threatening depletion of crude oil, it is imperative to find an alternative source of energy for sustainable development. Among all current options, hydrogen appears to be the most promising alternative to fossil fuels, because it has a high calorific value and is environmentally friendly. For safety and cost concerns, hydrogen storage in metal hydrides appears to be a more promising option at present, but there are still a lot of problems to be overcome for hydrogen storage and transportation. Because of the hydriding and dehydriding processes of metal hydrides are reversible endothermic and exothermic chemical reactions, heat transfer characteristics of hydrogen storage system would affect the hydrogen supply characteristics directly. In this work, we enhance the heat transfer in a metal-hydride reactor (MHR) by adding metal foam within the MHR. The mathematical model constructed in one previous work of our research group is used to simulate the hydriding and dehydriding processes in an MHR, and experimental data in a previous work are used to validate this model.

In the previous work of our group mentioned above, it was conclued that, with a fixed amount of metal hydride powder sealed in the MHR, saving a relatively small fraction of the reactor internal volume to accommodate a metal foam usually suffices to substantially facilitate heat removal from the system, thereby greatly shortening the hydriding time. However, for a metal foam of fixed apparent size, increasing it's volume fraction φmf would reduce the metal hydride content, and hence the maximum hydrogen storage capacity of the system. Consequently, if a prescribed amount of hydrogen is to be stored in the system, there exists an ``optimal"φmf value to minimize the charging time. However, in the previous study, the distribution of the metal foam is uniform, which at different distances from the cooling (heating) wall, differentφmf values may be needed to optimize the system performance. Therefore, in this thesis, we allow for a spatially varyingφmf distribution in an MHR . In this way, we could further enhance the performance of the system, and it wouldn't reduce the maximum hydrogen storage capacity of the system. Results of the study indicate that, in this way, we do make the hydrogen time and dehydrogen time reduce by 33%, and we could also make the mean hydrogen discharge rate increase by 33%. Moreover, we could make the steadiness of hydrogen discharge rate increase by 22%.

Keywords : Metal hydride system, Heat conduction augmentation, Metal foam, Hydrogen storage capacity, Distribution of metal-foam volume fraction, Hydriding time, Dehydriding time, Mean hydrogen discharge rate, Flow rate steadiness

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