Expanded Vermiculite-Based Calcium Chloride Hexahydrate Phase Change Materials: Preparation, Characterization, and Phase Change Kinetics

Solid-liquid phase change materials (PCMs) made from calcium chloride hexahydrate (CaCl2<middle dot>6H(2)O) offer benefits such as significant latent heat during phase change, high heat storage efficiency, low preparation costs, a nearly constant temperature exothermic process, and environmentally friendly attributes. However, they also face challenges like poor thermal conductivity, susceptibility to leakage, supercooling, and phase separation. The melt impregnation method prepared shape-stable composite PCMs using expanded vermiculite (EV) and CaCl2<middle dot>6H(2)O as raw materials. The layered pore structure of EV can be used as an encapsulation matrix to prevent the leakage of the CaCl2<middle dot>6H(2)O liquid phase. Adding 1 wt% strontium chloride hexahydrate (SrCl2<middle dot>6H(2)O) nucleating agent and 3 wt% copper nanoparticle thermal conductivity enhancer can reduce the supercooling by 8 degrees C and increase the thermal conductivity by 0.2092 W/(m<middle dot>K). The kinetic equation effectively describes the non-isothermal melt crystallization process. An increase in the cooling rate creates a thermal hysteresis effect on melt crystallization; the faster the cooling rate, the lower the temperature at which crystallization begins and the shorter the duration required for crystallization to complete. Both SrCl2<middle dot>6H(2)O and copper nanoparticles can reduce the crystallization activation energy, which is the essential reason for lowering the supercooling of CaCl2<middle dot>6H(2)O.