Preparation and thermal properties of a new hydrated salt phase change material without phase separation

This article discusses the use of hydrated salts as phase change materials for heat accumulators in distributed energy systems. Despite their potential, challenges like phase separation and supercooling hinder their widespread use. Common solutions with nucleating agents and thickeners often fall short. The study explores permanent solutions through composite materials and investigates new ways to maintain stability. Two new eutectic hydrated salts are introduced: SAT+SMN (sodium acetate trihydrate + sodium metasilicate nonahydrate) and SAT+LAD (sodium acetate trihydrate + lithium acetate dihydrate). The common ion effect reduces the solubility of nucleating agents, creating durable crystal seeds to trigger nucleation and reduce supercooling. In terms of thermal properties, SAT+SMN with a 20 % SMN mass fraction has a melting point of 52.2 °C and a latent heat of 248.4 J/g. SAT+LAD with a 10 % LAD mass fraction melts at 49.7 °C with a latent heat of 212.8 J/g. Supercooling in SAT+SMN is reduced to less than 0.5 °C, and in SAT+LAD, it drops to less than 3 °C. After 500 cycles, SAT+SMN maintains a supercooling degree within 0.5 °C with only a 0.02 % decrease in latent heat, demonstrating excellent thermal stability. The introduction of hydrated salts with more polar molecules in SAT increases the difference in the number of hydrogen bonds and bond energy between the solid and liquid states. This leads to new crystals with different lattice parameters and smaller cell sizes. While traditional stirring achieves uniform mixing up to 2 μm, ultrasonic mixing allows for a more even distribution, crucial for effective heat storage.