Latent heat thermal energy storage (LHTES) systems utilizing phase change materials (PCMs) are vital for enhancing the flexibility and reliability of renewable energy applications. However, the low thermal conductivity of PCMs often limits their charging and discharging rates in triplex-tube heat exchanger (TTHX) configurations. This study proposes an innovative TTHX design featuring internally interrupted twisted fins (ITFs) to overcome this limitation. Three-dimensional transient simulations, using the enthalpy–porosity and solidification/melting models, were employed to systematically evaluate the effects of key geometric parameters—including fin number (N) and twisted ratio (T_r)—on PCM thermal performance during both melting and solidification. Results indicate that increasing fin number and reducing the twisted ratio considerably enhance melting and solidification kinetics. Specifically, with N = 4, PCM melting time was shortened by 25.6% (343.8 s), and the average charging rate increased from 66.2 W to 89.8 W; lowering the twisted ratio to T_r = 2.5 further decreased melting time by 33.1% (446.0 s) and raised the charging rate to 103.6 J/s. Similar trends were observed in discharging: N = 4 reduced solidification time by 6.5%, and T_r = 2.5 by 16.5%, with respective increases in average heat release rates to 40.6 W. While the addition of ITFs slightly reduces PCM volume, the gains in heat transfer efficiency are significant with negligible impact on overall latent heat storage. These findings demonstrate that ITFs offer a tunable, highly effective strategy for accelerating both charging and discharging in TTHX-based LHTES units, providing actionable insights for the optimal design of advanced energy storage systems for renewable integration.

Phase-change thermal storage,Triplex tube heat exchanger,Interrupted twisted fins,3D numerical simulation