三水合乙酸钠复合相变材料的循环特性研究

Thermal cycling study on sodium acetate trihydrate composite phase-change material

三水合乙酸钠单位体积潜热约为同熔点下石蜡的2倍,但是具有严重的相分离和高过冷度,限制了其使用。本工作设计了一种使用半导体热电制冷片的循环测试装置,大幅缩短了循环实验周期,以用来研究三水合乙酸钠的循环特性。在过冷度稳定性探究中,通过添加十二水合磷酸氢二钠和纳米氧化铝为成核剂,以及羧甲基纤维素钠为增稠剂,进行了0~500次循环测试。实验结果表明该复合材料在高循环后仍然可以有效的自发成核,并保持相对稳定的过冷度。在潜热稳定性探究中,通过三水合乙酸钠相图分析发现无水乙酸钠在水中的低溶解度是使其相分离的主要原因。为了降低复合相变材料潜热损失,通过增大十二水磷酸氢二钠含量以适当降低无水乙酸钠与结合水比例。结果表明,在500次循环后复合相变材料平均过冷度约为5~8℃,相变潜热与初始时大致相等,能够保持稳定。本研究为三水合乙酸钠的应用提供了参考,同时半导体热电制冷片的循环测试装置也可以用于其他相变材料循环特性研究。

The latent heat per unit volume of sodium acetate trihydrate is about twice compared with that of paraffin wax at the same melting point.However,sodium acetate trihydrate has the disadvantages of phase separation and high subcooling,which limit its application.A thermal cycling device using a semiconductor thermoelectric cooling module was designed to shorten the cycle period and improve the experimental efficiency of experiments to study the stability of sodium acetate trihydrate.In the investigation of the stability of subcooling,a thermal cycling test was performed for 500 times on a sodium acetate trihydrate composite by adding disodium hydrogen phosphate dodecahydrate and nanoalumina as nucleating agents and sodium carboxymethyl cellulose as thickening agent.Experimental results show that this composite can nucleate effectively after 500 cycles and maintain a relatively stable supercooling.In the investigation of latent heat stability,the analysis of the phase diagram of sodium acetate trihydrate showed that the low solubility of anhydrous sodium acetate in water is the main reason for its phase separation.The content of disodium hydrogen phosphate dodecahydrate was increased to reduce the ratio of anhydrous sodium acetate to the bound water to reduce the latent heat loss of the composite phasechange material appropriately.The results showed that the average subcooling degree of the composite phase-change material was 5~8℃under a high number of cycles,and the latent heat of phase change retained similar values.The results in this paper can be helpful for the application of sodium acetate trihydrate,and thermal cycling setup using thermoelectric modules can be used for the studies of other phase-change materials.