Study on preparation and thermal performance of NaOH-NaNO3-EG composite phase change thermal storage material

The NaOH-NaNO 3 system exhibits excellent application potential in the medium-temperature thermal energy storage field owing to its high phase change enthalpy. However, when determining the eutectic composition ratio using the traditional proportion method, it is not only time-consuming and labor-intensive but may also miss the optimal ratio. In this study, the eutectic points of this composite system were predicted via FactSage software, yielding 3 sets of data. The corresponding molar ratios of NaOH/(NaOH + NaNO 3 ) are 0.28, 0.6, and 0.81, respectively, and the prediction results were verified to be accurate through DSC analysis. Based on this, the eutectic material with a molar ratio of NaOH to NaNO 3 of 6:4 was selected, designated as NN-PCM, and then compounded with 2–10 wt% expanded graphite (EG). Studies indicate that the sample compounded with 6 wt% EG (denoted as NN-PCM-6EG) is the optimal composite material: its thermal conductivity reaches 3.38 W/(m·K), which is a 256% increase compared to pure NN-PCM; its thermal diffusivity is 0.78 mm 2 /s, representing a 290% improvement; meanwhile, it exhibits good shape stability. Furthermore, the phase change enthalpy of this composite material is 114 J/g, with a phase change temperature of 262 °C. After 200 cycles, the fluctuation range of its phase change enthalpy is controlled within 3%. Verified by ANSYS thermal simulation, NN-PCM-6EG possesses an excellent thermal response rate; additionally, introducing a fin structure into the heat transfer system can significantly enhance the system's heat transfer efficiency.