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.

The Potential Environmental and Social Influence of the Inorganic Salt Hydrates Used as a Phase Change Material for Thermal Energy Storage in Solar Installations

“…However, the authors point out that there are studies with these substances in which the supercooling was not completely eliminated, possibly due to the low content of the additives. Xu et al [68] believe that CaCl 2 •2H 2 O plays an important role in reducing the supercooling and can be helpful in adjusting the freezing enthalpy. Xu et al [69] noticed that adding 0.02 wt.% to the CaCl 2 •6H 2 O. nano-sheet GO, the degree of supercooling is reduced by about 61.6%, In addition, SrCl 2 •6H 2 O 0.8% by weight can reduce the degree of supercooling of the CaCl 2 •6H 2 O sample to approximately 76.5%.…”

Inorganic salt hydrate for thermal energy storage application: A review

“…At high cooling rates, supercooling of up to 10°C was observed and it takes more time for nucleation at lower cooling rate. Cui et al 46 studied the thermal properties of CaCl 2 based PCM (water + varying composition of CaCl 2 and CaCl 2 ·2H 2 O). The PCM composition with 66.21 wt% CaCl 2 ·2H 2 O as additive observed to be reducing the supercooling degree by about 96.8% (from 24.7 to 0.8°C).…”

Preparation and Performance Analysis of Modified Sodium Acetate Trihydrate

“…The raw material is abundant, and is harmless to the environment. With these advantages, SAT can be widely used in solar heat and waste heat storage [ 10 , 11 , 12 , 13 ]. However, similar to most hydrated salts, SAT has serious undercooling and phase separation problems in the melting or solidification process.…”