Multi-variable optimization of metal hydride hydrogen storage reactor with gradient porosity metal foam and evaluation of comprehensive performance

Hydrogen storage performance for metal hydride (MH) reactor is restricted by the poor thermal conductivity of MH. In this study, the gradient porosity metal foam was added into MH reactor for enhancing heat transportation (GMF reactor), and its hydrogen absorption performance was investigated numerically in detail. Then, thermal resistance analysis was conducted to analyze the heat transportation in GMF reactor, and Genetic Algorithm was applied for optimizing metal foam distribution under different conditions. It was indicated that the hydrogenation performance for optimized two-layer GMF reactor was increased by 11.5% compared with uniform metal foam reactor (UMF reactor). The optimization results indicated that the optimal volumetric fractions of metal foam (VFMF) are about 0.08 for both optimized GMF reactor and UMF reactor with the trade-off of hydrogen storage capacity and hydrogen absorption rate. Then, a new indicator of comprehensive hydrogen storage performance (CHSP) for MH reactor was proposed, which includes the influence of hydrogen storage rate, hydrogen storage capacity, volumetric storage density and gravimetric storage density. Besides, the hydrogenation performance for optimized GMF reactor was improved with metal foam layer increasing, and the optimal porosity distribution was gradually approaching a specific power exponent trend. It was showed that the hydrogenation performance for power-exponent GMF reactor was increased by 2.8% and 18.2% compared with that of optimized four-layer GMF reactor and UMF reactor, respectively.