Numerical Investigation Of Heat Transfer Enhancement In A Copper Sphere-Based Decay Heat Exchanger With Paraffin Wax Using Cfd Simulations

The efficient management of decay heat remains a critical concern for nuclear reactor safety systems. This study uses computational fluid dynamics (CFD) to provide a thorough numerical analysis of a passive decay heat exchanger system's heat transfer performance. simulations in Ansys Fluent. Two configurations were analyzed: spheres constructed of solid copper and spheres filled with paraffin wax as a phase change material (PCM). The system consisted of a 50 mm diameter cylindrical pipe housing three copper spheres, each with a 35 mm diameter and a 6 mm heating element generating 100 watts of power. Simulations were conducted for Reynolds numbers ranging from 5000 to 15000. The findings revealed that integrating PCM significantly enhanced heat transfer efficiency. Specifically, In comparison to solid copper, the heat transfer coefficient increased by 4% as a result of the latent heat of fusion of paraffin wax (200,000 J/kg) absorbing and releasing energy during the phase transition process. Temperature contours highlighted dynamic phase change progression, with maximum temperatures near the heating element reaching 604.04 K after 200 seconds. Furthermore, the study evaluated the influence of varying Reynolds numbers on thermal performance, showing that higher values improved convective heat transfer. The results underscore the potential of PCM-filled copper spheres to enhance thermal regulation in passive heat exchangers, with significant implications for improving nuclear reactor safety during shutdown and emergency scenarios.