Phase change characteristics and supercooling suppression of D-mannitol enhanced by ZnO nanoparticles

D-mannitol (DM) becomes a highly potential medium-temperature phase change material (PCM) for thermal energy storage due to the high latent heat and good thermal stability, but the supercooling of DM lowers the heat release quality and thus hinders its large-scale industrial application. In this study, the supercooling suppression behaviors of DM with ZnO nanoparticles as nucleating agents were examined by analyzing the phase change characteristics and influencing factors on the supercooling of DM. The temperature history method was employed to study the isothermal phase transition characteristics with variations in particle concentration, particle size, and supercooling temperature difference, while the non-isothermal phase transition was evaluated using differential scanning calorimetry (DSC). The results show that supercooling temperature difference and ZnO nanoparticle concentration play more important roles in inhibiting the supercooling of DM as compared to the particle size. The supercooling degree of DM decreases with an increase in the ZnO nanoparticle concentration, and tends to be stabilized when the mass fraction reaches 2.0 %. The thermal conductivity of D/Z-2.0 %-25 nm was 1.113 W center dot m(-1) K-1, which was improved by 51.2 % over that of pure DM. X-ray diffraction (XRD) results show that the addition of ZnO does not alter the crystal arrangement of DM, indicating that only physical mixing occurs without chemical reaction. The cyclic tests demonstrate excellent thermal stability of the DM/ZnO. This study is significant because it demonstrates a potential method for enhancing thermal conductivity and inhibiting supercooling of DM with ZnO nanoparticles, and hence the efficient operation of medium-temperature thermal energy storage.