Investigation on charging enhancement of a latent thermal energy storage device with uneven tree-like fins

•Uneven tree-like fin is designed and optimized for energy charging enhancement.•Melting behavior with natural convection is numerically studied and analyzed.•Synergetic enhancement of natural convection and heat conduction is analyzed.•The fill angle and central-angle gradient are recommended to be 300° and 8°.•The total melting time of optimized energy storage units decreases by 46–49%. The charging intensification of latent thermal energy storage (LTES) devices has an important meaning for solar energy applications. For a more uniform temperature and faster melting rate of LTES devices, uneven tree-like fins are applied and optimized here. Numerical research of melting behaviors in tree-like finned LTES devices is performed with a particular focus on fin layouts. The melting interface transformation and transient temperature distribution in four LTES devices are examined. Moreover, the roles of fill angle and central-angle gradient in melting performance are studied for the optimization of uneven tree-like fins. The results indicate that uneven tree-like fins considerably improve energy charging performance since the heat conduction enhancement exceeds the free convection suppression. Compared with uniform tree-like fins, the uneven tree-like fins lead to a more uniform temperature distribution and consistently faster melting rate by the synergetic improvement of free convection and heat conduction in LTES devices. More significantly, the optimal fill angle and the central-angle gradient are suggested to be 300° and 8° for maximizing the melting performance. Correspondingly, the complete melting time of the optimal LTES devices with heterogeneous and gradient tree-like fins respectively decrease by 49% and 46% compared to LTES devices with uniform tree-like fins.