Enhancing cyclic charging-discharging performance of a latent heat storage unit using tree-shaped fins: Effects of fractal level and bifurcation angle on heat transfer and entropy generation

The low thermal conductivity of organic phase change materials limits the latent heat thermal energy storage performance. Most studies on tree-shaped fins examine melting or solidification separately, while this study numerically investigates the heat transfer and entropy generation characteristics of lauric acid during a consecutive melting–solidification process. Compared with rectangular fins, tree-shaped fins reduce the melting time, solidification time, and total process time by up to 45.81%, 47.23%, and 46.79%, respectively, and increase the energy storage power and energy release power by up to 84.58% and 90.22%, respectively. Relative to the one-level fractal cases, increasing the fractal level respectively reduces the melting time and solidification time by up to 21.21% and 28.74%, and respectively increases the energy storage power and energy release power by up to 27.07% and 43.58%. Furthermore, increasing the bifurcation angle from 30° respectively reduces the melting time and solidification time by up to 40.00% and 43.08%, and respectively increases the energy storage power and energy release power by up to 66.60% and 78.54%. Heat transfer entropy generation dominates the total entropy generation. Relative to rectangular fins, the total integrated heat transfer entropy generation for tree-shaped fins decreases by up to 33.67% and 43.92% during melting and solidification processes, respectively, while the corresponding total integrated flow friction entropy generation respectively decreases by up to 45.29% and 87.50%. Within the investigated range, the tree-shaped fin case with a fractal level of three and a bifurcation angle of 150° provides the best overall phase change performance.