Experiments, Simulation and Heat Transfer Analysis on Hydrogen Absorption/Desorption in Mg2Ni Metal Hydride Systems

• Main Authors: T.W.Huang, 黃宗偉
• Other Authors: H. C. Tien
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/52402081525836814209

碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 96 === Most studies in the literature dealt with minute quantity of Mg-based metal hydrides (such as Mg2Ni). This work investigated the absorption/desorption capability of a practical (1kW) hydrogen storage tank filled with 4.5kg Mg2Ni. A comparison and related discussion was made between numerical and experimental results. Two types of reaction tanks were considered in this study, namely, a electric-heating tank and a gas-heating tank. The latter one closely simulates use of the waste heat coming from gas power plants. In the aspect of electric-heating reaction tank, the numerical results indicated that under the condition of charging pressure of 17 bar and wall temperature of 150℃, the hydrogen absorbed in 150 minutes could reach 83 moles, equivalent to the theoretical value of hydrogen absorption (18.4 mole/kg) for 4.5kg Mg2Ni. It was also shown that the effect of pressurized cooling water was not so significant. Moreover, the reaction tank could release hydrogen up to 90% of the theoretical value of hydrogen absorption in 150 minutes. As for the experimental work for the electric-heating reaction tank, due to non-uniform grain size of Mg2Ni powder as well as frequent malfunction of some control valves, the activation results were below expectation. The other type of the reaction tank considered in this study is of the form of a double-pipe design, which contains 4.5kg Mg2Ni in the inner pipe while hot or cool air flows in the finned space between the inner pipe and the outer pipe. Use of fins is to increase the heat transfer area and to fulfill the cooling/heating requirement during hydrogen absorption/desorption processes. Due to uniformly small size (below 1mm) of Mg2Ni, the absorption/desorption capability of the gas-heating tank reached 75% to 77% of the theoretical value (18.4 mole/kg). Both numerical simulations and experiments were conducted for this tank. The results were qualitatively in agreement with the numerical results for the electric-heating tank. Finally, the reaction tank was connected to a 1 kW fuel cell with a hydrogen storage buffer tank in between. As the pressure inside the buffer tank reaches a pre-set value, hydrogen is then released to drive the fuel cell. It was found that the fuel cell worked well in connection with the gas-heating tank. The results obtained in this study will be helpful in developing more practical hydrogen-electricity systems.