Study on performance optimization of sodium sulfate decahydrate phase change energy storage materials

In this paper, sodium sulfate decahydrate (SSD) with a phase transition temperature of 32 °C was selected as the phase change energy storage material. However, SSD has the problems of large degree of supercooling, obvious phase stratification, and low thermal conductivity. To address these issues, a new SSD composite phase change energy storage material was synthesized by adding certain amounts of nucleating agents, thickeners, and high thermal conductivity agent to SSD. The results showed that when the addition of nucleating agent Na2B4O7·10H2O and thickener carboxymethyl cellulose (CMC) reached an optimal formulation ratio of SSD:Na2B4O7·10H2O:CMC = 100:5:3, the supercooling degree of the SSD composite phase change material was only 1.5 °C. Moreover, the heat release time of the phase change process was 25 min, and no phase stratification occurred. When expanded graphite with high thermal conductivity was added with the mass ratio of 9%, the effect on the supercooling degree of the SSD composite energy storage material was small, and the thermal conductivity increased by 3.9 times, reaching 2.13 W m−1 K−1. Differential scanning calorimetry method and step cooling curve method were used to test the decay rate of the thermal properties of the new composite phase change energy storage material, and the results were relatively close.