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A Study of Hydrogen Storage Performance for Mg2Ni Bed and Design of the Heat Exchange System for Metal-hydride Reactors
|Authors: ||Hao-Wei Weng|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
metal hydride (MH) reactors;variable conductivity;reaction rate;cycling effect;numerical simulation
|Issue Date: ||2011-06-30T07:26:07Z
|Abstract: ||本論文探討小型鎂鎳儲氫合金(Mg2Ni)反應容器之吸放氫性能，研究方法以數值模擬為主，測試結果則參考之前王志源論文。本研究也對實用型鎂鎳合金反應容器熱交換系統進行設計，以供後續研究之用。 在儲氫合金床之吸放氫數值模擬方面，本論文採用Sung與Deng之理論估算Mg2Ni合金床之可變熱傳導係數，並與吸放氫數值模擬程式相結合。模擬結果與採用固定熱傳導係數之結果接近，此點顯示取適當且固定之合金熱傳導係數模擬吸放氫過程不致造成太大誤差。 有鑑於自製儲氫合金的吸放氫反應速率隨反應次數增加而減緩，本文以指數函數的形式描述吸放氫反應速率常數，數值模擬結果較原有數學模型更接近測試結果。這種方式可適用於其他儲氫合金。 在實用型反應容器內含4.5公斤Mg2Ni熱交換系統之設計方面，本文採用双套管(Double-pipe)的設計以冷、熱空氣對反應容器行冷卻或加熱作用。內管與外管之間加入鰭片以增加熱傳面積，如此設計可使反應容器在較小的空氣質流率及低中流速下(吸放氫空氣流速分別為10及12 )，可達到反應容器吸放氫之放熱與吸熱需求。|
The objective of this thesis is to investigate the performance of hydrogen absorption/desorption for a small metal hydride (MH) reactor. This is accomplished mainly by numerical simulation. The testing results are extracted from Wang . The present work also intends to design the heat exchange system for a practical Mg2Ni reactor. In the aspect of numerical simulation for a MH reactor, a theoretical model developed by Sung and Deng  is used for calculating the variable effective conductivity of the Mg2Ni bed. This model is cast in the computer program for simulating the hydrogen absorption/desorption of the MH reactor. The results obtained are compared with previous numerical results  based on constant heat conductivity. The difference between them is generally small. It indicates that using a proper fixed value for the conductivity of the MH bed does not cause significant errors. Since the testing results  clearly show that the reaction rate for absorption/desorption decays as the number of reaction cycles increases. A simple mathematical model for describing the reaction rate constant is proposed. The model is in the form of an exponential function. The numerical results accounting for this effect match the experimental results more closely. This model can be applied to other metal hydrides. As for the design of the heat exchange system for a practical MH reactor, a double-pipe design is adopted. The inner pipe is filled with 4.5 kg MH powder. Cool or hot air flows in the annulus for cooling or heating the MH bed. A number of fins are added to the outer surface of the inner pipe for increasing the heat transfer area. Based on calculation, such design with fins needs low air speed (10 m/s and 12 m/s for hydrogen absorption/desorption, respectively) to satisfy the cooling/heating load for hydrogen absorption/desorption of the MH bed.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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