This study presents a numerical investigation of a novel helical two-pass coaxial PCM-based latent heat thermal energy storage system designed for compact energy storage applications. The two-pass configuration enables bidirectional heat transfer along a helical flow path. This helps improve fluid–PCM interaction, melting uniformity, and thermal penetration within a limited storage volume. To further enhance performance, helically twisted fins with 12, 36, and 60 turns are incorporated along the inner PCM wall. The results show that the inclusion of twisted fins markedly accelerates PCM melting. The 60-turn fin configuration reduces the total melting time by approximately 22% in comparison with the finless two-pass case while achieving a more uniform temperature distribution. This improvement is because of the combined influence of bidirectional heat transfer, the helical flow geometry, and fin-assisted conduction, which together promote deeper thermal penetration and more uniform melting. Overall, the findings highlight the potential of the proposed helical two-pass coaxial design as an effective solution for enhancing the charging performance of compact PCM-based energy storage systems.
