| 摘要(英) |
This thesis presents an experimental study of the impact of heat transfer on the performance of hydrogen absorption and desorption processes using LaNi5 hydrogen storage alloy. A hollow cylindrical storage tank and a cylindrical tank with a heat pipe and internal fins were designed and made to test the hydrogen storage characteristics and to demonstrate the storage efficiency improved by the heat transfer application.
Results from the experiments showed that when LaNi5 absorbed hydrogen, heat was released by the exothermic reaction. The rising temperature in turn raised the metal’s equilibrium pressure for hydrogen absorption and reduced the pressure difference from the hydrogen supply. Accordingly the hydriding reaction slowed down. Therefore, the greater the supply pressure of hydrogen and lower the ambient temperature of water bath, the quicker hydrogen could be charged into the hollow cylindrical tank. On the other hand, when the metal hydride desorbed hydrogen, heat was taken by the endothermic reaction. The descending temperature in turn reduces the metal’s equilibrium pressure for hydrogen desorption and reduced the pressure difference to the back pressure. The dehydriding reaction then slowed down as a result. Therefore, the higher the ambient temperature, the quicker hydrogen could be discharged from the storage tank. The above results indicated that enhancing heat transfer between the metal powders and the surrounding water bath should improve the performance of the storage tank.
To this end, a pilot design of hydrogen storage tank was made with a heat pipe and internal fins to increase the heat transfer rate. The heat pipe facilitated heat exchange between the central region of tank and the ambient water bath. The internal fins increased the effective conductivity of the metal bed. Experiments showed that hydrogen reactions occurred more evenly in the fined tanked than in the bare cylindrical tank. Accordingly, hydrogen uptake reached three times quicker and the alloy maximum temperature reduced as much as 20°C in the hydriding case, and hydrogen release rate was 44% quicker and the lowest temperature was increased by about 10°C in the dehydriding case for the heat transfer enhanced design. This thesis demonstrates that heat transfer enhancement could effectively improve the performance of hydrogen storage tank and may serve as a reference for the design of hydrogen storage tanks based on metal hydrides.
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| 參考文獻 |
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