Adjustment of phase change temperature using KCl to develop composite phase change materials based on super absorbent polymer as carrier for use in building energy conservation

In the present work, a Na2HPO4·12H2O-KCl/SAP composite phase change material (CPCM) adapted to the comfortable indoor temperature of the human body has been successfully prepared. The CPCM was developed by physical mixing of Na2HPO4·12H2O (DSP) as the main PCM, KCl as temperature regulator and super absorbent polymer as carrier. In addition, the CPCM was characterized by various techniques, and its thermal properties were analyzed. The results showed that the phase change temperature (Tm) of DSP could be adjusted from 35.8°C to 32.7°C by KCl and the DSP-KCl mixture containing 4% KCl had a high enthalpy value (241.5 kJ·kg-1). The cooling curve test found that adding 0.75% nano-α-Al2O3 as nucleating agent could greatly reduce the supercooling degree of DSP-KCl mixture to 3.39°C. Adding 14% SAP into the mixture can solve the leakage and reduce the supercooling degree and thermal conductivity. The resulting CPCM with 14% SAP added had appropriate Tm (26.9°C), high enthalpy value (153.5 kJ·kg-1), low supercooling degree (1.34°C) as well as thermal conductivity (0.3079 W·K-1·m-1) and excellent thermal reliability. These results indicated that the CPCM was suitable for the field of building energy conservation.