A Comprehensive Parametric CFD Investigation on Packed Bed Thermal Energy Storage System with Encapsulated Solid-Solid Phase Change Materials in Discharging Mode

The increasing growth of energy consumption and the decreasing trend of fossil reserves as well as the increase of environmental pollutants have made energy storage a very important issue. Therefore, the technology of using phase change materials for energy storage has been developed in recent years. The employing of phase change materials (PCMs) allows latent heat to be stored through thermal energy, which is the best way to store thermal energy. In this paper, the performance of a packed bed encapsulated solid-solid phase change material (SS-PCM) has been investigated. SS-PCMs have features such as greater stability along the charge and discharge process, higher flexibility in system design, very small volume changes and no leakage. Discharge operation of encapsulated SS-PCM packed bed via computational fluid dynamics (CFD) modeling with COMSOL Multi-physics platform is investigated, and the results of simulation versus experimental data that from the papers obtained are validated. The effects of storage tank height, SS-PCM capsule diameter and heat transfer fluid velocity on the temperature profile of packed bed was researched. As well as, enthalpy changes of storage tank have been studied. It is found that reducing the height of thermal storage tank and increasing the inlet velocity of heat transfer fluid (HTF) in the storage tank caused the faster discharge of packed bed. The diameter of the SS-PCM capsule also affects the completion of the packed bed discharge process. Reducing the diameter of the capsule shortens the discharge process time.