Optimization of capsule diameters in cascade packed-bed thermal energy storage tank with radial porosity oscillations based on genetic algorithm

Abstract

The packed-bed thermal energy storage system (PBTES) has broad application prospects in renewable energy, such as for solar, hydraulics, biomass, and geothermal. This study varied the capsule diameter arrangement of the PBTES using a genetic algorithm (GA) to optimize the thermal performance of the cascaded three-layer PBTES during charging. When considering the oscillatory distribution of the radial porosity, the thermal energy storage (TES) rate density was used as an objective function to evaluate the system’s thermal performance. The TES rate density of PBTES was calculated for more than 4000 capsule diameter arrangements. The results indicate that the tank-to-capsule diameter ratio significantly affects the radial porosity distribution, velocity, and temperature distribution of PBTES. The optimal capsule diameter arrangement in the range of 15 mm ≤d≤ 40 mm was obtained as d1 = 15.58 mm, d2 = 21.78 mm, and d3 = 27.68 mm. Compared with the original model, the optimal model’s charging time was reduced by 33.90%, the TES rate density improved by 37.07%, and the cost per unit of heat storage increased by 92.41%. The results show that the GA is a powerful tool for optimizing PBTES structures.