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.