Hybrid geometric optimization of wavy tubes with Y-shaped fins for enhanced solidification in latent heat storage systems

This study addresses the inherent low thermal conductivity of phase change materials (PCMs) by introducing a hybrid passive enhancement strategy that integrates wavy inner tube geometry with Y-shaped fin arrays within a vertical double-pipe heat exchanger. The novelty lies in optimizing both macro-scale surface area and micro-scale heat diffusion paths to accelerate solidification. A comprehensive parametric analysis was conducted using ANSYS Fluent with enthalpy-porosity method, examining 18 cases with varying wave amplitudes (2.5–10 mm), fin lengths, Y-fin angles (15°–30°), and fin-to-shell distances (2–6 mm). Results show that Case 17, featuring a 10 mm wave amplitude, 2 mm fin-shell gap, and 30° Y-fin angle, achieved complete solidification in 1565s (42 % faster than the smooth-wall baseline and recorded a peak discharge rate of 113.14W, nearly tripling the base case's 38.3W. These improvements are attributed to enhanced natural convection, reduced thermal resistance, and uniform heat distribution. Compared to previously reported designs, the proposed configuration offers a synergistic gain in both heat transfer rate and PCM utilization. This work is significant as it demonstrates that coupling geometric and fin-based strategies in a hybrid design can substantially overcome PCM thermal limitations, paving the way for more efficient and compact thermal energy storage systems.