Study of the effect of layered structure on phase separation and heat transfer properties of phase change materials

Energy storage devices are poised to take center stage in future distributed energy systems. Currently, the primary obstacles hindering the widespread adoption of hydrated salts in phase change accumulators are issues related to phase separation and thermal conductivity during extended cycling periods. In this study, we address these challenges by introducing deionized water into the mix and carefully controlling the material's layer height. We conducted a thorough investigation of the optimal interaction ratios and analyzed the resulting improvements in thermal storage capacity and cycling stability. To mitigate the phase separation problem, we incorporated deionized water while precisely regulating the material's layer height. This approach effectively allows the aqueous layer of the hydrated salt phase change material to make contact with or even cover the anhydrous salt layer, resolving the phase separation issue. The addition of a small amount of water destroys the original hydrogen bonding network of sodium acetate trihydrate to reduce its heat storage capacity, but the latent heat value is still at a high level. Moreover, the phase change material exhibits remarkable stability and heat storage capacity when maintained at a 2 cm layer height with 3 % deionized water. After 500 cycles, the latent heat value only experienced a minimal decrease of 0.78 %, demonstrating excellent cycle stability. In practical applications, it is essential to avoid phase separation in phase change materials by appropriately adjusting the material layer height or increasing the water content as needed when implementing them in heat accumulators. Additionally, our study proposes the use of a layered fin structure for heat accumulators, which was validated through Fluent simulations. These layered fins are exceptionally well-suited for directing heat transfer within the accumulator, offering superior heat transfer performance compared to other non-continuous fin structures.