Supercooling reduction in water-based PCMs using soya oil ester: thermal characterization and nucleation analysis

Abstract

Water-based phase change materials (PCMs) are attractive for low-temperature thermal energy storage due to their high latent heat; however, their application is limited by severe supercooling caused by inefficient nucleation. This study evaluates the nucleation efficiency of soya oil ester as an additive for reducing supercooling of water-based PCMs. PCM samples were prepared with soya oil ester concentrations of 10%, 12.5%, 15%, and 17.5% by weight, each with a total mass of 100 g. Thermal characterization was performed using Differential Scanning Calorimetry (DSC) and the T-history method. DSC measurements were conducted in triplicate for each composition, while T-history tests employed parallel samples under identical cooling conditions. The temperature and enthalpy uncertainties of the DSC system were ±0.1 °C and ±2%, respectively, and the thermocouples used in the T-history setup exhibited an uncertainty of ±0.5 °C. The results show a substantial improvement in nucleation efficiency, with supercooling reduced from 7.5 °C in pure water to 1.2, 0.8, 0.5, and 0.2 °C for ester concentrations of 10%, 12.5%, 15%, and 17.5%, corresponding to a suppression efficiency of up to 97.3%. The freezing onset temperature increased from −19.5 °C to −12.0 °C, indicating enhanced heterogeneous nucleation. Crystallization shifted from multi-step behavior in pure water to a single, reproducible event in modified PCMs. Although latent heat decreased slightly, it remained suitable for cold thermal energy storage. Overall, soya oil ester significantly improves nucleation performance and thermal reliability of water-based PCMs.