Optimization based methodology to design metal hydride reactor for thermal storage application

Abstract

A metal hydride based thermal energy storage system offers high energy density, provides longer storage time and requires less storage space compared to either conventional or phase change material based thermal energy storage systems. However, the design of such system is considered significantly complex. In this study, Taguchi method coupled with grey relational analysis was used to optimize the design parameters i.e. diameter of helical tube (dh), major diameter of helical tube (dm), number of turns of helical tube (N) and velocity of heat transfer fluid (Vf) for the helical tube heat exchanger embedded inside metal hydride reactor for thermal energy storage application. These parameters were optimized subjected to achieve maximum reaction fraction (C0) and maximum outlet temperature of heat transfer fluid (To). The performance of all experiments in the orthogonal array which were used for Taguchi and Grey relational analysis were evaluated by 3-D numerical simulations performed in commercial software COMSOL 5.3a. This methodology used is significantly computationally efficient as the number of required simulations reduced by 90% as compared to the conventional parametric study-based methodology. The required number of simulations reduced from 81 to 9 with the use of proposed methodology. Further, the added advantage of this methodology is, it enables to estimate an optimized level of the parameters by considering all the objective functions (C0, To) simultaneously. Lastly, the performance of the optimally designed systems was compared with all the orthogonal array experiments and it was found out that the optimized system designs were found to have better performance considering the objective parameters i.e., C0 and To as compared with the other experiments of the orthogonal array.