基于CaCl₂·2H₂O/CaCl₂的盐水合物相变材料的制备及过冷度改性

Xu Xiaoxiao, Dong Zhijun, Memon Shazim Ali, Bao Xiaohua, Cui Hongzhi

College of Civil Engineering, Shenzhen University, Shenzhen 518060, China.

School of Traffic and Environment, Shenzhen Institute of Information Technology, Shenzhen 518060, China.

Materials (Basel). 2017 Jun 23;10(7):691. doi: 10.3390/ma10070691.

Salt hydrates have issues of supercooling when they are utilized as phase change materials (PCMs). In this research, a new method was adopted to prepare a salt hydrate PCM (based on a mixture of calcium chloride dihydrate and calcium chloride anhydrous) as a novel PCM system to reduce the supercooling phenomenon existing in CaCl₂·6H₂O. Six samples with different compositions of CaCl₂ were prepared. The relationship between the performance and the proportion of calcium chloride dihydrate (CaCl₂·2H₂O) and calcium chloride anhydrous (CaCl₂) was also investigated. The supercooling degree of the final PCM reduced with the increase in volume of CaCl₂·2H₂O during its preparation. The PCM obtained with 66.21 wt % CaCl₂·2H₂O reduced the supercooling degree by about 96.8%. All six samples, whose ratio of CaCl₂·2H₂O to (CaCl₂ plus CaCl₂·2H₂O) was 0%, 34.03%, 53.82%, 76.56%, 90.74%, and 100% respectively, showed relatively higher enthalpy (greater than 155.29 J/g), and have the possibility to be applied in buildings for thermal energy storage purposes. Hence, CaCl₂·2H₂O plays an important role in reducing supercooling and it can be helpful in adjusting the solidification enthalpy. Thereafter, the influence of adding different percentages of Nano-SiO₂ (0.1 wt %, 0.3 wt %, 0.5 wt %) in reducing the supercooling degree of some PCM samples was investigated. The test results showed that the supercooling of the salt hydrate PCM in Samples 6 and 5 reduced to 0.2 °C and 0.4 °C respectively. Finally, the effect of the different cooling conditions, including frozen storage (-20 °C) and cold storage (5 °C), that were used to prepare the salt hydrate PCM was considered. It was found that both cooling conditions are effective in reducing the supercooling degree of the salt hydrate PCM. With the synergistic action of the two materials, the performance and properties of the newly developed PCM systems were better especially in terms of reducing the supercooling degree of the PCM. The novel composite PCMs are promising candidates for thermal energy storage applications.

当水合盐被用作相变材料（PCM）时，存在过冷问题。在本研究中，采用了一种新方法来制备一种水合盐PCM（基于二水氯化钙和无水氯化钙的混合物），作为一种新型PCM系统，以减少CaCl₂·6H₂O中存在的过冷现象。制备了六个具有不同CaCl₂组成的样品。还研究了二水氯化钙（CaCl₂·2H₂O）和无水氯化钙（CaCl₂）的性能与比例之间的关系。在其制备过程中，最终PCM的过冷度随着CaCl₂·2H₂O体积的增加而降低。用66.21 wt%的CaCl₂·2H₂O获得的PCM将过冷度降低了约96.8%。所有六个样品，其CaCl₂·2H₂O与（CaCl₂加CaCl₂·2H₂O）的比例分别为0%、34.03%、53.82%、76.56%、90.74%和100%，均显示出相对较高的焓（大于155.29 J/g），并且有可能应用于建筑物的热能存储目的。因此，CaCl₂·2H₂O在降低过冷度方面起着重要作用，并且有助于调节凝固焓。此后，研究了添加不同百分比的纳米SiO₂（0.1 wt%、0.3 wt%、0.5 wt%）对一些PCM样品过冷度降低的影响。测试结果表明，样品6和样品5中的水合盐PCM的过冷度分别降至0.2℃和0.4℃。最后，考虑了用于制备水合盐PCM的不同冷却条件的影响，包括冷冻储存（-20℃）和冷藏（5℃）。发现这两种冷却条件在降低水合盐PCM的过冷度方面都是有效的。在两种材料的协同作用下，新开发的PCM系统的性能和特性更好，特别是在降低PCM的过冷度方面。这种新型复合PCM是热能存储应用的有前途的候选材料。