The present study prepared nanocomposite phase change materials (PCMs) based on calcium chloride hexahydrate (CaCl2·6H2O) with gamma aluminum oxide (γ-Al2O3) nanoparticles to characterize phase change behavior, such as the supercooling degree, phase change temperature, latent heat, thermal conductivity, and thermal stability. Results demonstrate that thermal conductivity and heat transfer of the CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs are significantly enhanced and supercooling of CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs is suppressed. Moreover, a 50 run cycling test verifies that the CaCl2·6H2O nanocomposite PCMs contained with 1 wt % γ-Al2O3 possesses enhanced thermal behavior. The degree of supercooling is within the range of 0.3–1.1 °C; the maximum reductions in the latent heat is 5.9%; and no phase segregation was observed. The CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs presented acceptable thermal reliability, chemical stability, and heat transfer characteristics, thereby reflecting its acceptability for low-temperature solar thermal energy storage applications.

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In this work, the calcium chloride hexahydrate/diatomite/paraffin composite phase-change material (PCM) was fabricated by impregnating calcium chloride hexahydrate into diatomite and further coating with paraffin. Scanning electron microscope (SEM) results showed that the hydrated salt could be impregnated into a diatomite well and the paraffin could be coated on a diatomite surface. The Fourier transform infrared spectroscopy (FT−IR) demonstrated that no chemical interactions were found between calcium chloride hexahydrate and diatomite matrix except that of hydrogen bonds. The melting and crystallizing enthalpy of the coated composite PCM are 108.2 and 98.5 J/g, respectively. The supercooling of hydrated salts was weakened due to the nucleation positions on the huge surface of diatomite and the coating effect of the paraffin, and phase segregation was eliminated in 100 cycles by microvolume effect in the pores of the diatomite. Additionally, coated composite PCM and composite PCM exhibited better thermal stability and reliability than hydrated salts due to the interactions of hydrated bonds, the capillary force and the surface tension as well as the coating of the paraffin. After the 100 cycles, the melting and crystallizing enthalpy of coated composite PCM declined to 106.2 and 93.8 J/g from 108.2 and 98.5 J/g, dropping by 1.8% and 4.8%, respectively. The coated composite PCM with well thermal properties, thermal reliability, and chemical stability was a promising PCM candidate for heat-energy storage applications.

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