Preparation and Supercooling Modification of Salt Hydrate Phase Change Materials Based on CaCl2 2H2O/CaCl2

Abstract

Salt hydrates have issues of supercooling when they are utilized as phase change materials (PCMs). In this research, a new method was adopted to prepare a salt hydrate PCM (based on a mixture of calcium chloride dihydrate and calcium chloride anhydrous) as a novel PCM system to reduce the supercooling phenomenon existing in CaCl2 6H2O. Six samples with different compositions of CaCl2 were prepared. The relationship between the performance and the proportion of calcium chloride dihydrate (CaCl2 2H2O) and calcium chloride anhydrous (CaCl2) was also investigated. The supercooling degree of the final PCM reduced with the increase in volume of CaCl2 2H2O during its preparation. The PCM obtained with 66.21 wt % CaCl2 2H2O reduced the supercooling degree by about 96.8%. All six samples, whose ratio of CaCl2 2H2O to (CaCl2 plus CaCl2 2H2O) was 0%, 34.03%, 53.82%, 76.56%, 90.74%, and 100% respectively, showed relatively higher enthalpy (greater than 155.29 J/g), and have the possibility to be applied in buildings for thermal energy storage purposes. Hence, CaCl2 2H2O plays an important role in reducing supercooling and it can be helpful in adjusting the solidification enthalpy. Thereafter, the influence of adding different percentages of Nano-SiO2 (0.1 wt %, 0.3 wt %, 0.5 wt %) in reducing the supercooling degree of some PCM samples was investigated. The test results showed that the supercooling of the salt hydrate PCM in Samples 6 and 5 reduced to 0.2 C and 0.4 C respectively. Finally, the effect of the different cooling conditions, including frozen storage (����20 C) and cold storage (5 C), that were used to prepare the salt hydrate PCM was considered. It was found that both cooling conditions are effective in reducing the supercooling degree of the salt hydrate PCM. With the synergistic action of the two materials, the performance and properties of the newly developed PCM systems were better especially in terms of reducing the supercooling degree of the PCM. The novel composite PCMs are promising candidates for thermal energy storage applications.