本文針對裝填鑭鎳合金(LaNi5)之儲氫罐進行數值模擬，並且分析儲氫罐在吸放氫過程中的熱流特性。儲氫罐內分成兩個區域，分別為上層膨脹區以及下層合金區，膨脹區為預留合金膨脹所需的空間。由於合金在吸氫時會產生熱量，放氫時則需提供熱量，因此藉由能量方程式添加熱源項來描述此機制。氫氣和合金在反應過程中質量的增減則利用連續方程式來描述。膨脹區以及合金區的流動的現象分別使用那維爾-史托克斯方程式( Navier-Stokes equation )和佛許海默-布里克曼方程式(Forchheimer-Brinkman equation)來描述。上述方程式配合適當的邊界以及初始條件，利用ANSYS Fluent 12.0此套裝軟體完成本研究的數值計算。 從模擬結果可知，罐體內壁面處能快速與外界進行熱交換，故吸放氫的反應速率較快。本文亦模擬了添加熱管以及鰭片之熱傳增強型罐體，結果顯示在熱管以及鰭片周圍的熱傳性能較佳，故吸放氫速率能有效提升。 本文藉由改變環境條件以分析各種參數對於吸放氫反應的影響。由模擬計算結果可知： 對吸氫反應而言，降低環境溫度以及提升供氫壓力可加快吸氫反應速率；改變鰭片材料對於吸氫反應影響有限；不同的熱管熱傳極限吸氫速率亦不同，但隨著熱傳極限的增加，其對吸氫速率的影響將逐漸變小；而改變不同熱管熱阻值對於吸氫速率則影響不大。 對放氫反應而言，提高環境溫度以及降低出口壓力可加快放氫反應速率；改變鰭片材料對於放氫反應影響亦有限；由於在放氫反應時罐內熱傳量較小，故改變熱傳極限以及熱管熱阻值對放氫反應的影響皆不明顯。This study presents a numerical simulation for hydrogen absorption and desorption processes using LaNi5. The hydrogen storage canister is assumed to comprise two physical domains, which include an expansion volume region atop a alloy bed. The expansion volume provides the spare space which allow for alloy to expand during the absorption processes. Energy equations are used to describe the temperature changes in the alloy bed induced by the heat release during the hydriding processes and heat absorption during the dehydriding processes. The continuity equations are used to describe the mass balance between the alloy and hydrogen. The Brinkman-Forchheimer and Navier-Stokes equations are used to describe the gas flow within the porous alloy bed and expansion volume, respectively. The mathematical model developed is solved using ANSYS Fluent 12.0. Results of simulation show that both absorption and desorption rates are higher in the alloy regions close to the finned heat pipe and the tank wall. Parametric analyses are also performed on the absorption rates and desorption rates. Results show that for the absorption process, the absorption rates are larger for lower environmental temperature and higher supply pressure. Inversely for the desorption process, the desorption rates are larger for higher environmental temperature and lower outlet pressure. The effects of the fin conductivity are negligible for both absorption and desorption processes. For the absorption process, the higher the heat pipe power limit, the faster the absorption rates. However, changing heat pipe power limit has little impact on the desorption rates because of the relatively mild desorption process. Results also show that the resistance of heat pipes is typically low that changing the heat pipe resistance only has little impact on both the hydrogen absorption and desorption rates.
