Preparation and thermal performance enhancement of sodium thiosulfate pentahydrate-sodium acetate trihydrate/expanded graphite phase change energy storage composites

Heat energy storage using phase change materials (PCMs) in electric radiant floor heating system (ERFHS) is a favorable solution to the improvement of energy efficiency. In this paper, the sodium thiosulfate pentahydrate (Na2S2O3 center dot 5H(2)O,STP)-sodium acetate trihydrate (CH3COONa center dot 3H(2)O, SAT) eutectic mixture was prepared by adding 30 wt.% STP and 70 wt.% SAT. Sodium carboxymethyl cellulose (CMC) and sodium pyrophosphate (Na4P2O7,TSPP) were added to fabricate the modified STP-SAT phase change material. The results showed that almost no phase separation occurred in STP-SAT eutectics with 1 wt.% CMC and 0.4 wt.% TSPP, and its supercooling degree was reduced to 0.3 ?C. The thermal properties of the composite phase change material (CPCM) with different contents of expanded graphite (EG) were studied. And the experimental results showed that the composite containing 8% EG displayed a high phase change enthalpy (186.0 kJ/kg) and an ignorable supercooling degree. The addition of EG increased the thermal conductivity of STP-SAT from 0.748 to 2.92 W/m.K. The thermal reliability of CPCM was confirmed through the thermal cycle test and thermogravimetric analysis (TGA). After 200 thermal cycles, CPCM exhibited fantastic thermal stability and reliability.