三水合醋酸钠/膨胀石墨复合相变材料的制备及其储热性能

Preparation and Thermal Storage Properties of Sodium Acetate Trihydrate-Expanded Graphite as Phase Change Composite

水合盐储能材料普遍存在热导率低、过冷度大及相分离问题.本文通过熔融共混制备了以三水合醋酸钠(SAT)为主体的复合相变材料(CPCM).采用膨胀石墨(EG)作为高导热添加物强化导热系数,同时作为成核剂改善其过冷度问题.采用黄原胶(XG)为增稠剂改善复合相变材料的相分离问题.研究了复合相变材料的导热性能、相变性能及热稳定性,并基于该复合相变材料(SAT/EG/XG)搭建了高储热密度的相变储热器,研究了该装置在85℃热源、20℃冷源下的储放热性能.结果表明:膨胀石墨的加入可明显增强热导率及消除过冷度.添加2%~4%(质量分数)膨胀石墨,复合相变材料热导率可达1.12~1.81 W/(m·K),为纯SAT热导率的2~3倍,且添加0.5%~1.2%(质量分数)黄原胶可明显抑制相分离.复合相变材料具有很好的热稳定性,50次循环后其熔化温度保持在58.0℃左右,凝固温度稳定在57.6℃左右,无明显过冷度,相变焓为250~255 kJ/kg.基于该复合相变材料的储热器的储热密度可达442.7 kJ/L,是传统水箱的1.7倍,储放热效率达96.4%,具有明显的储热优势.

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—1.81 W/(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—255 kJ/kg.Moreover,the thermal storage device filled with composite phase change material has a heat storage density of 442.70 kJ/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.