ANALYSIS OF THE EFFECTIVENESS OF CURVED FINS IN THE PHASE CHANGE PROCESS IN A TRIPLE-PIPE HEAT EXCHANGER

Latent heat thermal storage offers advantages over sensible or thermochemical storage, as it exhibits high energy density and operates at a nearly constant temperature. However, phase change materials (PCMs), essential in these systems, have low thermal conductivities, significantly impacting their response time. Fins continue to be one of the main techniques used to enhance heat transfer, as they impact the cycle time of these systems and have a low manufacturing cost. However, studies have shown that straight fins are not always the best option. Fins with different geometries can better penetrate PCM regions and improve efficiency. Thus, the objective of this work is to analyze, using computational fluid dynamics (CFD), the influence of curved fins in a triple-tube heat exchanger on the melting (charging) and solidification (discharging) processes. Four geometries were proposed, with fins installed on the inner or outer tubes, curved upwards or downwards, and compared against straight fins. The PCM used was RT82, and the system was assessed under three temperature differentials: 10, 15, and 20 K, totaling 42 cases. Results demonstrated that curved fins increased effectiveness by 10% and 11% in melting and solidification, respectively, compared to straight fins. Temperature increases resulted in a nonlinear reduction in process time, with a greater reduction between 10 and 15 K than between 15 and 20 K. Upward-curved external fins exhibited the highest phase change rates, upwards of 4% and 9% in the solidification and melting processes, respectively, and achieved an average solidification time 5.3% shorter than other geometries.