Magnesium based metal hydride reactor incorporating helical coil heat exchanger: Simulation study and optimal design
Magnesium based metal hydride reactor incorporating helical coil heat exchanger: Simulation study and optimal design
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DOI：
10.1016/j.apenergy.2013.12.071
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发表时间：
2014-10
期刊：
影响因子：
11.2
通讯作者：
Zhen Wu;Fusheng Yang;Zao-xiao Zhang;Z. Bao
中科院分区：
文献类型：
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作者：
Zhen Wu;Fusheng Yang;Zao-xiao Zhang;Z. Bao
镁基金属氢化物被认为是氢能系统实际应用中最常用的材料之一。传热传质过程对镁基金属氢化物反应器的储氢性能有重要影响。在反应器中加入螺旋盘管换热器是改善传热传质性能的有效途径。本文提出了一种新的带螺旋盘管换热器的镁基金属氢化物反应器的三维模型，并用商用软件COMSOL多物理V3.5a进行了求解。在数值模拟的基础上，首次对采用传统直管换热器和新型螺旋盘管换热器的反应器储氢性能进行了比较。对比结果表明，螺旋盘管换热器由于具有二次循环的特性，在改善反应器性能方面比直管换热器有更好的效果。系统地分析了初始条件、换热流体换热系数和螺旋盘管几何形状等关键参数对螺旋盘管换热器反应器性能的影响。研究发现，较大的初始氢气压力和较低的初始温度有利于吸氢动力学的改善，因为氢化反应的驱动力较大。优化设计结果表明，较小的无量纲螺距，即螺距与螺旋径的比例越小，传热传质性能越好。当换热流体的换热系数为500W/m−2K−1时，无量纲螺距为0.333的反应器在3.0K和523K下表现出最好的储氢性能。在这种情况下，大约95%的吸氢过程在1000W/m S左右完成。
Magnesium based metal hydride has been viewed as one of the most commonly-used materials in the practical applications of hydrogen energy systems. The heat and mass transfer processes have significant effects on the hydrogen storage performance of magnesium based metal hydride reactors. Incorporating helical coil heat exchanger into the reactor could be an effective way to improve the performance of heat and mass transfer. In this work, a new three-dimensional model for magnesium based metal hydride reactor with helical coil heat exchanger is proposed and solved using the commercial software package COMSOL Multiphysics V3.5a. The comparison of hydrogen storage behaviors between the reactors incorporating the traditional straight pipe and new helical coil heat exchangers is firstly conducted based on the numerical simulation. The comparison results show that the helical coil heat exchanger has better effect on improving the characteristics of reactor than the straight pipe heat exchanger due to its secondary circulation. The effects of key parameters, including the initial conditions, heat transfer coefficients of heat transfer fluid and helical coil geometry on the characteristics of reactor with the helical coil heat exchanger are also analyzed systematically. It is discovered that larger initial hydrogen pressure and lower initial temperature are beneficial to the improvement of hydrogen absorption kinetics, because of the greater driving force for the hydriding reaction. The results of optimal design suggest that smaller non-dimensional pitch, the ratio of helical pitch to helical diameter, improves the heat and mass transfer performance. The reactor with 0.333 of non-dimensional pitch exhibits the best hydrogen storage behaviors under 3.0 MPa and 523 K, when the heat transfer coefficient of heat transfer fluid is 500 W m−2K−1. Approximately 95% of hydrogen absorption process is completed within about 1000 s in this case.