A Study of Hydrogen Storage Performance for Mg2Ni Bed and Design of the Heat Exchange System for Metal-hydride Reactors

• Main Authors: Hao-Wei Weng, 翁浩偉
• Other Authors: Hwa-Chong Tien
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/88842032246387081277

碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 95 === 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 [39]. 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 [19] 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 [39] 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 [39] 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.