空气能蓄冷用相变材料研制及热物性表征

Preparation and characterization of phase change materials for air energy storage

针对自然冷源在建筑空气调节中的应用,以癸酸-月桂酸(CA-LA)低共熔混酸为相变材料,纳米Fe_(2)O_(3)为添加剂,膨胀石墨(EG)为基质材料,采用化学分散、超声振荡和物理吸附的方法制备CA-LAFe_(2)O_(3)/EG复合相变材料,并对材料进行性能表征。结果表明纳米Fe_(2)O_(3)质量分数为0.8%时与CA-LA混合均匀性较好,具有成核作用,消除了CA-LA的过冷度;EG质量分数为5.88%时,对CA-LAFe_(2)O_(3)(质量分数0.8%)具有较好的包覆效果,傅里叶变换红外光谱(FTIR)显示复合材料内部未发生化学反应,各物质之间属于物理吸附;纳米Fe_(2)O_(3)粒子和EG可加快材料相变过程,较CA-LA、CA-LA Fe_(2)O_(3)(质量分数0.8%)的冷却与结晶过程总时间缩短了39.4%,CA-LA Fe_(2)O_(3)(质量分数0.8%)/EG(质量分数5.88%)对应时间缩短78.2%,有利于空气能蓄冷过程的顺利进行;CA-LA Fe_(2)O_(3)(质量分数0.8%)/EG(质量分数5.88%)的相变焓为124.70kJ/kg,融化初始温度为18.66℃,结晶起始温度为19.87℃,较CA-LA的焓降低3.4%,融化与结晶过程温度区间均增大,材料的导热性能增强。定型复合相变材料热响应与受压方向有关,受压面切向方向温度响应速度远大于受压面法向方向,相变储能换热器设计时应考虑材料导热的各向异性特点。

Phase change materials with excellent performance are very important for the application of natural cooling source in building air conditioning.Composite phase change materials CA-LAFe_(2)O_(3)/EG was prepared using the CA-LA eutectic acid as phase change materials,nano-Fe_(2)O_(3) as additive,and expanded graphite(EG)as matrix materials by chemical dispersion,ultrasonic oscillation and physical adsorption.The properties of the materials were characterized.The results showed that it was better mixing uniformity with CA-LA when the mass fraction of nano-Fe_(2)O_(3) was 0.8%,which eliminated the supercooling of CA-LA.When the mass fraction of EG was 5.88%,it had a good adsorption on CA-LA Fe_(2)O_(3)(0.8%).FTIR spectrum revealed that there was no chemical reaction in CA-LAFe_(2)O_(3)/EG.The crystallization process showed that adding nano-Fe_(2)O_(3) particles and EG can accelerate the cooling and crystallization process.The cooling and crystallization time was reduced 39.4%by adding only nano Fe_(2)O_(3) particles and 78.2%by adding nano-Fe_(2)O_(3) and EG,which was conducive to the cold storage process.DSC results indicated that the enthalpy of CA-LAFe_(2)O_(3)(0.8%)/EG(5.88%)/EG was 124.70kJ/kg,which was 3.4% lower than that of pure CA-LA.The oneset melting temperature was 18.66℃ and the oneset crystallization temperature was 19.87℃.Compared with CA-LA the temperature range during melting and crystallization was increased and the thermal conductivity of the material was enhanced.The thermal response of shape stabilized composite phase change materials was affected by the anisotropy of expanded graphite and its thermal response was related to the compression direction.The temperature response speed in the tangential direction of compression was far greater than that in the normal direction.The anisotropy of the materials should be considered in the design of phase change energy storage heat exchangers.