Design optimization on solidification performance of a rotating latent heat thermal energy storage system subject to fluctuating heat source

The combination of latent heat storage (LHS) technology with the Organic Rankine Cycle represents a widely recognized solar thermoelectric conversion means. However, this technology is hindered by the instability of solar energy and the poor thermal conductivity of thermal storage materials. This study addresses the challenges posed by solar energy fluctuations by implementing a sinusoidal heat source condition during the heat release process of LHS system. Furthermore, a comprehensive approach is taken to enhance heat transfer, incorporating both active methods such as rotational conditions, and passive methods using metal nanoparticles and high-performance fins. The Taguchi method is employed to optimize rotation speed, heat source amplitude, and half-period of the latent heat storage unit, and the resulting heat release performance is compared between different structures and the optimized structures. The findings from optimal design analysis reveal that rotation speed has the most significant influence on mean heat discharging rate and solidification time, followed by the heat source amplitude and half-cycle period. There is a notable interaction between heat source amplitude and half-cycle period. Compared to the initial structure, the optimal structure identified through the optimal design shortens the solidification time by 11.18%, increases the mean heat discharging rate by 13.04% and raises the average temperature response by 18.82%. Furthermore, the addition of Al2O3 nanoparticles further enhances heat discharging properties. Specifically, the presence of 2.5% and 5% Al2O3 nanoparticles shortens unit solidification time by 9.52% and 18.83% and increases the mean heat release rate by 7.69% and 17.26%. It is noted that the incorporation of rotating-fit nanoparticles partly compensates for the limitations of increased viscosity and particle settlement associated with metal nanoparticles, although it does not fully address the challenges related to reduced heat storage/release.