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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.

The mature and scale utilization of renewable energy is restricted by the deficient efficiency of latent heat storage (LHS) technology. To address this, an innovative Vicsek fractal fin is first proposed herein for the heat charging/discharging rate enhancement. The phase transition behavior and thermal characteristics of the innovative LHS unit are solved numerically and compared to the traditional one, employing the enthalpy–porosity algorithm and a two-dimensional transient model. The results indicate that Vicsek fractal fins remarkably promote the thermal efficiency of LHS units. Compared to the traditional LHS units, innovative LHS units with Vicsek fractal fins, respectively, reduce the melting/solidification duration by 16.1% and 28.7%. The melting process is divided into early thermal conduction, subsequent convective thermal transport, and later thermal conduction, while solidification processes are dominated by the initial natural convection and the subsequent continuous heat conduction. Moreover, the impact of free convection is higher on melting processes than on solidification processes. Importantly, the efficient heat transfer path of Vicsek fractal fins allows the inherent natural convection suppression to be much weaker than the improvement level of heat transfer efficiency, facilitating the interstitial thermal transport between the phase change material (PCM) and fins and improving the overall temperature uniformity of LHS units.

An experimental investigation has been carried out to know about the performance improvement of a household refrigerator using phase change material (PCM). PCMs are used as latent heat thermal storage system to enhance the heat transfer of the evaporator. PCM is located behind the five sides of the evaporator cabinet in which the evaporator coil is immersed. Water (melting point 0°C) and Eutectic solutions (melting point −5°C) are used as PCMs for this experiment at different thermal loads. Depending on the types of PCM and thermal load, around 20–27% COP improvement of the refrigeration cycle has been observed with PCM with respect to without PCM. With the increase of the quantity of PCM (0.003 to 0.00425 m³) COP increases about 6%. Between two different PCMs the COP improvement for Eutectic solution is higher than Water. The experimental results with PCM confirm that, depending on the thermal load and the types of PCM average compressor running time per cycle is reduced significantly and it is found about 2–36% as compared to without PCM.