Parametric and sensitivity analysis of metal hydride hydrogen storage systems for development of novel design charts

Hydrogen storage is the biggest challenge towards the widespread utilization of hydrogen as an energy carrier. One of the methods is solid-state storage of hydrogen in the metal hydride, which is safe, volumetrically efficient, and involves an optimal set of operating conditions. However, designing reactors for metal hydride storage involves much thermal management since the absorption and desorption are exothermic and endothermic reactions, respectively. Many optimization and simulations are involved before arriving at a suitable metal hydride reactor design for a particular application. This study focuses on developing easy-to-use design charts to evaluate reaction fractions inside the metal hydride bed for various combinations of parameters. First, the parameters affecting the reaction fraction are selected, and the range for each of these parameters is defined. The dependence of each parameter on the reaction fraction is analysed, maintaining the mean value of the remaining parameters. The LaNi5 is used as a metal hydride for this study. A two-dimensional (2-D) mathematical model is developed to evaluate the effect of these parameters on reaction fraction. Further, based on this detailed parametric study, a sensitivity analysis has been carried out to determine the most significant parameters. It was observed from this parametric and sensitivity analysis that among the considered parameters, the volume of the reactor (amount of hydrogen to be stored) and length to diameter ratio have a more dominant effect on the reaction fraction followed by supply pressure and thermal conductivity of metal hydride. However, the external temperature of heat transfer fluid (ie, the ambient temperature) does not significantly affect the reaction fraction. Hence, this parameter is assumed to be constant in developing design charts. Also, based on this analysis, the range of parameters is redefined for design charts. Further, this 2-D mathematical model and parametric and sensitivity analysis are used to develop the design charts. These design charts use the most sensitive parameters and demonstrate the effect of all the other parameters on the reaction fraction. Finally, the method of using these design charts and their accuracy is explained for reaction fraction evaluation for a particular set of parameters. These charts are easy-to-use and accurate for the quick preliminary reaction fraction estimation for metal hydride hydrogen storage system.