A novel flat coil tube heat exchanger for metal hydride hydrogen storage reactors

Abstract

Metal hydride (MH) based hydrogen storage is one of the potential methods for achieving higher volumetric storage densities. However, its poor thermal conductivity limits heat transfer during exothermic hydriding and endothermic dehydriding processes. Hence, heat transfer augmentation is essential in MH reactors to speed up the charging and discharging of hydrogen. The present study proposes a novel flat coil tube heat exchanger with a spiral fin for heat transfer augmentation. It offered superior performance than conventional single and double helical tube heat exchangers, taking 35.3 and 16.7% less time for 90% storage time. Further, optimization of design parameters (pitch and fin thickness) is carried out considering several key parameters such as weight ratio (WR), gravimetric exergy output rate (GEOR), and energy efficiency (EE). A pitch of 30 mm with a fin thickness of 0.25 mm is optimum according to a novel performance index. The influence of the operating parameters (H2 supply pressure and heat transfer fluid inlet temperature) on the absorption performance is investigated for the optimized design. Finally, a single desorption case is presented at 1 bar and 333 K to gain insights about desorption behavior.