金屬氫化物顆粒床熱傳導係數量測設計之模擬分析

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題名:	金屬氫化物顆粒床熱傳導係數量測設計之模擬分析
作者:	張銘珊;Chang,Ming-shan
貢獻者:	機械工程學系
關鍵詞:	儲氫合金;熱傳導係數;metal hydride;thermal conductivity
日期:	2013-08-07
上傳時間:	2013-10-08 15:28:19 (UTC+8)
出版者:	國立中央大學
摘要:	本文建立數學模型並藉由套裝軟體COMSOL Multphysics 4.3模擬金屬氫化物顆粒床等效熱傳導係數量測實驗之過程，透過實驗之模擬驗證等效熱傳導係數理論模型之合理性並探討其受壓力、溫度、含氫濃度之影響，發現固體熱傳導係數決定等效熱傳導係數之基本大小，而受尺寸效應影響之氣體熱傳導係數則決定其隨壓力變化之幅度。並且，等效熱傳導係數與壓力、溫度、含氫濃度為正相關，而與孔隙率為負相關，其中壓力對等效熱傳導係數之影響最為明顯。此外，模擬實驗過程以探討反應裝置於實驗過程中之熱傳特性，得知儲氫合金於吸放氫過程受到上下端溫度差異裝置的影響，合金密度、溫度以及等效熱傳導係數皆沿軸向變化，而合金平衡壓則因溫度及合金密度由上而下遞增之影響於空間中大致呈均勻分布。金屬氫化物等效熱傳導係數量測裝置之絕熱效果對實驗之準確性而言是相當重要的因素，故利用量測裝置之半徑與高度尺寸參數進行絕熱效果之探討，發現裝置以扁平之圓盤設計時其絕熱效果較佳，而當罐體外型固定時，絕熱層外徑與待測材料半徑比值為1.65時有最佳徑向絕熱效果。 This study presents the effective thermal conductivity of metal hydride granular beds, consisting of the alloy powders and the void pores between the powders, using the theoretical model. Effects of hydrogen pressure, hydrogen content and bed temperature on the effective thermal conductivity are analyzed. Results show the heat transfer between the adjacent solid powders constitutes the fundamental part of the effective thermal conductivity. Heat transfer by the gas conduction, which is strongly affected by the size effect, determines the effective thermal conductivity change rate with pressure. The raises in pressure, temperature and hydrogen content result in a higher effective thermal conductivity of metal hydride bed. In contrast, the raise in porosity results in a lower effective thermal conductivity. This study also presents numerical simulation for the processes of measuring the effective thermal conductivity using an axial heat conduction device. Results from the simulation show the hydrogen content, temperature and effective thermal conductivity mainly change in the axial direction. The hydrogen equilibrium pressure however is uniform due to the combined effects of the hydrogen content and temperature. The insulation efficiency in the radial direction of the effective thermal conductivity measurement device is important to ensure the measurement accuracy. Results of parameter analysis show the device is better to have a flat disc shape than a long cylinder shape for the radial insulation. In addition, for fixing the outer diameter of the device, there is the best insulation effect if the radius ratio of the insulation layer to the test stack radius is 1.65 regardless of the material properties, which maximizes the axial heat rate to the relatively minimized radial heat rate.
顯示於類別:	[機械工程研究所] 博碩士論文

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