Thermal performance analysis of packed-bed thermal energy storage with radial gradient arrangement for phase change materials

The current paper investigates the radial gradient arrangement of phase change material capsules effect on the thermal behavior of a packed-bed latent thermal energy storage system. A transient two-dimensional dispersion-concentric model is developed to analyze the phase transition of phase change materials. Moreover, the heat transfer characteristics between air and phase change material capsules in four different packed bed systems are discussed in detailed. The results indicate that the use of radial gradient arrangement in the phase change material capsules significantly enhances the heat transfer performance of the system. The system pressure drop is apparently decreased when the radial gradient arrangement is taken into consideration. From case 1 to case 4, the overall energy efficiency is 84.16%, 80.43%, 83.55%, and 82.46%, respectively. The capacity ratio of case 1 is higher than all studied cases by 5.03%, 1.11%, and 3.74%, respectively. The utilization ratio of case 1 is higher than all studied cases by 5.15%, 1.45%, and 3.43%, respectively. Furthermore, considering the loss of pressure drop, it is found that case 3 is the most viable option of all the studied cases. This study provides a numerical basis for the thermal stability output and the structure optimization of packed bed system.