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Inspired by the snowflake structure, an innovative Koch-fractal fin is proposed to optimize the fin geometry of the latent heat thermal energy storage (LHTES) units. A model of unsteady heat transfer accompanied with phase change is developed and numerically analyzed to investigate the effect of fin structure on the discharging process of a LHTES unit. The dynamic response of heat release, the dynamic temperature response and solidification front evolution of a LHTES unit with Koch-fractal fins are discussed and compared with the corresponding radial fins. Furthermore, a comprehensive evaluation of thermal performance of LHTES units is conducted in terms of the TES capacity, TES rate and solidification time. The results indicate that the heat release rate of a LHTES unit with Koch-fractal fins is faster than that with radial fins. Moreover, because the Koch-fractal fins have advantages of higher specific surface area, faster heat flow path from point to surface and smaller thermal resistance arising from the reasonable spatial layout, the evolution of solidification front is faster and the temperature distribution is more uniform. The results of quantitative evaluation show that although the TES capacity is identical, the TES rate of a LHTES unit with Koch-fractal fins is six times that with radial fins. [ABSTRACT FROM AUTHOR]