Numerical studies on <scp>PCM</scp> 's contribution for thermal energy storage in continuous operation

Abstract The utilization of phase change materials (PCMs) holds immense promise for thermal energy storage due to their high latent heat capacity. However, the design of advanced continuous operation systems is currently hampered by the lack of a systematic framework for selecting the optimal PCM, leading to risks of inefficiency and unpredictable performance. This study directly confronts this challenge by establishing clear selection criteria based on a numerical investigation of simultaneous melting and solidification. We analyzed three paraffin‐based PCMs (RT 50, RT 35, and RT 27) under constant source (348 K) and sink (273 K) temperatures. The results reveal that achieving a stable, continuous melt fraction depends not on a single property like latent heat, but on the complex interplay between thermal diffusivity, driving forces, and convection, as quantified by Rayleigh and Prandtl numbers. RT 50 exhibited the most stable performance, attaining a steady melt fraction of 0.21 after 180 s and an average PCM temperature of 304.9 K, with Rayleigh numbers of 425 × 10 8 (charging) and 756 × 10 8 (discharging). In contrast, RT 27 and RT 35 showed continuously increasing melt fractions of 0.36 and 0.34 at 200 s, driven by higher thermal gradients (46 and 40 K, respectively) and Prandtl numbers (45.6 and 230), indicating unstable long‐term operation. This work provides a crucial, evidence‐based methodology for designing next‐generation, high‐efficiency thermal storage systems.