太阳能中温利用相变材料MgCl2·6H2O的热循环耐久性研究

摘要

In order to study the feasibility of magnesium chloride hexahvgrate(MgCl2·6H2O)as a PCM under medium temperature,six hundred accelerated thermal cycle tests had been conducted under sealed and unsealed conditions.The melting temperature and the latent heat of fusion,crystalline structure and degree of supercoo-ling were determined by differential scaning calorimetry (DSC),X-ray diffraction (XRD)and multiway temper-ature detector respectively.The results indicated that the decrease in latent heat of fusion of MgCl2·6H2O un-der unsealed condition was 54.2% and accompanied with a new phase MgCl2·4H2O after 200 cycles.The change in melting temperature,peak temperature of MgCl2·6H2O under sealed condition was ±1% and ±4%respectively,and the change in latent heat of fusion was and -15.2%-+1.5% except for the 300th melt/freeze cycle.MgCl2·6H2O solidified with a slight degree of supercooling in the range 0-2.2 ℃.It was indicated that MgCl2·6H2O under sealed condition was a promising phase change material for solar energy use under medium temperature.%分别在密封和未密封条件下对六水合氯化镁(MgCl2�6 H2 O)进行600次加速热循环实验,研究其作为太阳能中温蓄热材料的可行性.采用差示扫描量热仪、X射线衍射仪和多路温度测试仪测试不同次数热循环后样品的相变温度、相变潜热、晶体结构和过冷度.结果表明,未密封状态下,200次热循环后, MgCl2�6H2 O 的相变潜热降低54．2％,并有新相MgCl2�4H2 O 产生；密封状态下,600次热循环后, MgCl2�6 H2 O 的相变温度和峰值温度的变化分别在±1％和±4％内,相变潜热的变化在-15．2％~＋1．5％内(300次热循环后变化异常)；同时,MgCl2�6H2 O 凝固时几乎没有过冷现象,过冷度在0~2．2℃之间.密封状态下,MgCl2�6 H2 O 在太阳能中温蓄热应用中是一种很有发展前景的材料.