Heat transfer enhancement and performance study on latent heat thermal energy storage system using different configurations of spherical PCM balls

Abstract

Thermal energy storage (TES) systems utilizing latent heat storage substances have gained significant attention recently due to their large heat storage capacity and isothermal behavior during charging and discharging processes. However, many phase change materials (PCM) used for storage exhibit relatively low thermal conductivity. Prolonged surfaces like fins are incorporated in PCM balls to improve heat transfer performance. These fins significantly improve the overall performance of the TES system. This study conducted experiments to evaluate the performance of a latent heat thermal energy storage (LHTES) system using spherical balls filled with PCM, both with and without solid internal fins. Water was used as the heat transfer fluid (HTF) at a constant temperature of 70 °C, while paraffin served as the PCM with a melting temperature of 61 °C. Time-based temperature variation of HTF and PCM has been investigated for various HTF flow rates. Moreover, the effect of non-dimensional numbers, such as Reynolds, Rayleigh, Nusselt, and Stanton numbers, has also been investigated. Performance parameters such as thermodynamic efficiencies and entropy generation are analyzed. The heat storage process aims to get a highly efficient configuration for accumulating the maximum energy possible and higher exergy efficiencies during the charging process. The charging duration is reduced by 47.37 % when comparing the solid internal fin configuration at the higher flow rate (6 L/min) with the no fin configuration at the lower flow rate (2 L/min). At 100 min, the cumulative heat stored is higher in the solid internal fin configurations than in the configurations without fins. Furthermore, the internal fin configurations have less entropy generation than without fin configurations, justifying that providing solid internal fins in PCM balls enhanced the LHTES system performance.