Thermal performance study and optimization of a novel bidirectional cascade phase change thermal storage unit

Conventional cascaded latent heat thermal energy storage (LHTES) units are constrained by unidirectional phase change material (PCM) arrangements, resulting in asynchronous melting and extended melting durations in distal regions. These limitations hinder the broader adoption of LHTES systems in renewable energy applications. To address these challenges, a novel bidirectional cascaded PCM arrangement, integrating axial segmentation with radial layering is proposed in the paper. This design strategically organizes PCMs with decreasing melting points along both directions, thereby enhancing the internal temperature difference. Furthermore, the incorporation of high thermal conductivity fins significantly augments heat transfer, leading to a marked increase in the heat storage rate. The effects of PCM arrangement and copper plate angle on melting behavior, heat transfer performance, and thermodynamic characteristics were investigated by numerical simulation. The results show that the bidirectional arrangement reduces the melting time difference by 40.9% compared to the uniform layout. Following copper plate optimization, the melting time difference is reduced by 75.7% compared to the bidirectional arrangement, and by 85.6% compared to the uniform layout. This study demonstrates that a two-dimensionally cascaded PCM layout combined with optimized copper plate structures can significantly enhance the thermal performance of LHTES systems. The findings offer a new strategy for structurally optimizing vertical shell-and-tube LHTES units, with positive implications for overall efficiency and operational performance.