Latent heat thermal energy storage (LHTES) technology can alleviate the mismatch between the supply and demand of solar energy and industrial waste heat, but the low thermal conductivity of phase change materials (PCMs) is an issue that needs to be solved. In this work, the effects of the bifurcated fins on melting and solidification are studied, and local and global entropy generation are discussed. The radial lag time and the circumferential lag time were defined to evaluate thermal penetration and thermal uniformity. Subsequently, a novel arc-shaped fin configuration was proposed to further enhance the heat transfer. The results showed that attaching the bifurcated fins could effectively reduce the global entropy generation. Increasing the trunk fin length was beneficial to enhance the thermal uniformity and promote the melting process, while increasing the branch fin was more effective in the solidification process. Overall, thermal uniformity determined the phase change process. More importantly, the concentric arc-shaped fins significantly reduced the heat transfer hysteresis region, showed better thermal performance than straights fins, and the energy storage and release time were reduced by 52.7% and 51.6%, respectively.

In this paper, the enhancement of thermochemical energy storage by alkali metal chloride salts-doped Ca-based sorbents is revealed by experiments and DFT calculations. The results indicate that NaCl and KCl doping increases the reaction rate and cycle stability. Compared to CaO, the conversion of NaCl-CaO and KCl-CaO after one cycle is increased by 59.1% and 61.9%, respectively. This enhancement originates from the oxygen vacancies generated by Na₂O and K₂O and the significantly increased surface area by CaCl₂ as well as the sintering delay. The synergistic effect between Na₂O, K₂O, and CaCl₂ increases the reaction rate of calcium-based materials. Meanwhile, the penetration of low-viscosity molten NaCl and KCl into the calcium-based materials successfully segregates the CaO grains and allows the calcium-based material to maintain the porous structure after 80 cycles, thus exhibiting a high effective conversion rate. In addition, the KCl-CaO composites show the best combined performance in terms of effective conversion and averaged thermal energy density. This work paves the way for the application of chloride salts-doped calcium-based materials.

The inherent low thermal conductivity of phase change materials (PCMs) serious limits the thermal performance of latent heat thermal energy storage (LHTES) systems. In this study, the author proposed two operating modes (inside heating/outside cooling and inside cooling/outside heating)and designed seven fin configurations to improve the thermal performance and flexibility of the triple-tube LHTES unit. A transient two-dimensional numerical model was established to study the energy storage, release and simultaneous storage and release processes, and local and global entropy generation was analyzed. A comprehensive evaluation was used to propose the optimal combination of operating mode and fin configuration. Considering various performances, the combination of the operation mode of inside cooling/outside heating and the staggered fin configuration shortened the total time by 66.6% and increased the heat transfer rate by 5.6%, providing the best performance in both the continuous and simultaneous storage and release process.