THERMAL ENERGY CHARGING IMPROVEMENT OF A LATENT THERMAL ENERGY STORAGE SYSTEM VIA FRACTAL-BRANCHED FINS

The current study achieves a melting improvement of the latent thermal energy storage (LTES) system using fractal-branched fins (i.e., Y-type and T-type fins). A transient melting model with free convection in LTES systems is developed and numerically simulated with the enthalpy-porosity method. The effects of branched fins on the melting performance are discussed and compared to the traditional plate fin with emphasis on the roles of fin parameters. Besides, the optimized configuration is obtained by the response surface methodology (RSM) in terms of the total charging time. The results indicate that the branched fin expedites the melting process, especially for the T-type branched fin. Due to a more desirable fin layout, the LTES system using T-type branched fins presents a more uniform temperature field and faster melting rate, manifesting as the reduced total melting time by 5.6% compared to the Y-type branches. The melting process includes the pre-heat conduction dominated, free convection dominated, and post-heat conduction dominated stages. A T-type branched fin with moderate branch level (n), larger length index (alpha), and lower width fractal dimension (Delta) is favorable for the coordinated enhancement of heat convection and conduction. The RSM optimization implies the length index and branch level play more remarkable roles than the width fractal dimension in melting enhancement. To maximize the charging efficiency of LTES systems, the optimal parameters of T-type fin are alpha = 0.9, n = 4, and Delta = 1, which shortens the total charging time by 52.9% compared to the traditional plate fin.