Abstract: Salt hydrate as an energy storage material has the problems of low thermal conductivity, phase separation, and large supercooling. In this paper, a composite phase change material (CPCM) with sodium acetate trihydrate (SAT) as the main body is fabricated by melting blending. Expanded graphite (EG) is used as a high heat conduction additive to enhance the thermal conductivity, and as a nucleating agent to decrease supercooling degree simultaneously. Xanthan gum (XG) is used as a thickening agent to suppress the phase separation of the composite phase change material. The phase change properties, thermal stability and, thermal conductivity of the composite phase change materials are studied. A high energy-density heat storage device is built by using the composite phase change material (SAT/EG/XG) and its thermal property is analyzed by heating at 85℃ and cooling at 20℃. The results show that the addition of EG can obviously enhance the heat conductivity and eliminate the supercooling. With the addition of 2%—4% (mass fraction)expanded graphite, the thermal conductivity of CPCM reaches to 1.12—1.81W/(m·K), which is 2—3 times of the pure SAT. Besides, the addition of 0.5%—1.2% (mass fraction)XG can significantly inhibit phase separation. The composite phase change material has a good thermal stability. After 50 cycles, the melting temperature is kept at about 58.0℃, the solidification temperature is stable at about 57.6℃, there is no obvious supercooling, and the phase change enthalpy is 250—255kJ/kg. Moreover, the thermal storage device filled with composite phase change material has a heat storage density of 442.70kJ/L, which is 1.7 times that of the traditional water tank, and its heat storage and release efficiency reaches to 96.4%, which shows obvious advantages.

Key words: sodium acetate trihydrate, expanded graphite, latent energy storage, thermal conductivity, thermal performance