Optimization of thermal storage characteristics in molten salt phase change thermal storage units: A numerical analysis based on heat pipe arrangement patterns

The application of thermal storage units is one approach to mitigate the intermittency of clean energy, where heat transfer efficiency and thermal storage capacity are critical parameters. To enhance heat transfer and thermal storage performance, three models—Uniform-type, U-type, and V-type—were constructed, using NaNO3-KNO3-NaNO2 (7:53:40 wt%) as the phase change material (PCM). The impact of these different arrangements on the PCM melting process was investigated through computational fluid dynamics simulations. The results indicate that the model with the Uniform-type arrangement requires 91.76 min to achieve complete melting of the PCM. The optimal V-type arrangement achieved a phase change completion time of 45.16% relative to the Uniform-type arrangement with no significant increase in cost for the thermal storage unit component. After 40 min of thermal storage, its energy storage capacity reaches 24.14 × 103 kJ, which is 1.38 times that of the Uniform-type model. Mechanism analysis revealed that the temperature difference between the heat source and the PCM, along with their contact area, are two critical factors affecting the system's heat transfer efficiency. These findings provide a basis for the structural optimization of the thermal energy storage unit.