A novel fin efficiency concept to optimize solid state hydrogen storage reactor

Abstract

The process of heat-driven mass transfer involved in hydrogen storage within metal hydrides (MHs) demands implementing a heat transfer system (HTS) to facilitate faster hydrogen charging and discharging. One effective method to enhance heat transfer is utilizing an HTS equipped with fins and a cooling tube. Among the crucial factors for optimizing the reactor, fin efficiency (FE) plays a vital role, although it has not been explored in unsteady processes like the present one. This study introduces a novel FE technique to optimize fins in a conventional longitudinal finned tube MH reactor based on LaNi5. Due to the intricacies of the problem, making analytical estimation of FE challenging, the authors turned to the concept of reverse engineering. This approach utilizes simulated data's temporal temperature profiles to calculate the FE. The number of fins is varied from 4 to 12 while keeping the total fin weight constant. Heat transfer performance improved as the number of fins increased, but the FE deteriorated from 0.89 to 0.56 due to the reduction in fin thickness. A performance index (PI) that considers the number of fins is introduced to assess the overall performance. Its values are 0.58, 0.79, 0.96, 1.05, and 1.1 for configurations with 4, 6, 8, 10, and 12 fins, respectively. The configuration with 8 fins is deemed optimal because further increasing the number of fins led to only marginal improvements in PI value. Subsequent optimization of fin shape, precisely radial tapering, had a minimal impact on heat transfer performance. Finally, the desorption behavior was examined for the optimal configuration with 8 fins of constant thickness.