Experimental study on the performance of packed-bed latent thermal energy storage system employing spherical capsules with hollow channels

The applicability of packed bed latent thermal energy storage devices is restricted by the limited thermal conductivity of phase change materials (PCMs). As a cheap and simple heat transfer-enhanced construction, the hollow channel allows the heat transfer fluid to go through the capsule center directly where the melting rate of PCM would be enhanced. In this study, an experiment was conducted to explore the promotion effect of hollow channels. The influence of the hollow channels on the charging duration and outlet temperature characteristics at different inlet flow rates, inlet temperatures, and placement angles was investigated. The results showed that the charging rate was improved with a reduction in charging duration of about 16.6%. The improvement was consistent in scenarios with variable inlet temperatures and flow rates, with a difference of less than 1%. Furthermore, adding hollow channels resulted in a lower average outlet temperature. Finally, there is no significant influence of horizontal and vertical placements of the hollow channels on the performance of PBLTES. Therefore, random angle placement is advised to reduce costs in engineering. However, the addition of hollow channels drops the PCM filling rate by 3.7%, reducing latent thermal energy storage but increasing sensible thermal energy storage.