Improving the energy discharging performance of a latent heat storage (LHS) unit using fractal-tree-shaped fins

Abstract

The fractal tree-shaped structure has been demonstrated as a promising optimization method to maximize the point-area heat flow access. Aiming to enhance the energy discharging rate of the latent heat storage (LHS) unit, an innovative fractal-tree-shaped structure is introduced to construct the metal fin of a shell-tube LHS unit. An unsteady model of solidification heat transfer in a LHS unit with tree-shaped fins is developed and numerically analyzed using commercial CFD software, in an effort to demonstrate the improvement of the energy discharging performance for a latent heat storage unit using fractal tree-shaped fins. The transient temperature distribution, solid-liquid interface evolution, and dynamic changes of the liquid fraction and the sensible and latent heat in a tree-fin LHS unit are compared with those of a radial-fin LHS unit. The effects of length ratio and width index on energy discharge performance are examined and analyzed. The results indicate that the tree-shaped fin significantly improves the energy discharge performance of a shell-tube LHS unit. The tree-fin LHS unit possesses a faster solidification rate, higher energy discharge rate, and stronger temperature uniformity. The complete solidification time of the tree-fin LHS unit is decreased by 66.2% and its complete melting time is reduced by 4.4% when compared with the radial-fin LHS unit. For superior thermal energy discharge performance, the length of tree-shaped fins in a shell-tube LHS unit should be shorter inward and longer outward; the optimum length ratio is about 1.3 and an appropriate width index is 1.