Abstract:

Aiming at the problem that leakage always happen in the phase change process of octadecane, olefin block copolymer (OBC) is used as the packaging structure to prepare composite stereotyped phase change materials (PCMs). Meanwhile, the low thermal conductivity of octadecane is improved by adding expanded graphite (EG). The results show that when the mass fraction of OBC is 10%, the leakage will happen in the phase change process. However, leakage has not been observed when the mass fraction of OBC is equal to or higher than 20%. When the mass fraction of OBC is 20%, the phase change enthalpy of the composite PCM is 166.87 J/g, and lower than that of pure ocadecane (227.40 J/g) by 26.62%. The thermal conductivity of composite phase change materials with different mass fraction of EG increases with the increase of the content of EG. When the mass fraction of EG is 5%, the thermal conductivity of the composite PCM is 4.179 W/(m?K), which is about 16 times higher than that of the pure PCM [0.24 W/(m?K)], indicating that EG could effectively improve the thermal conductivity of the composite PCM. In addition, the phase change enthalpy of composite PCM with 5% EG was about 149.54 J/g, and there was no significant change in phase change temperature and enthalpy after 50 cycles, indicating that the thermal stability of the composite PCM is great. Therefore, the composite phase change material has the utilization potentiality in building energy conservation.

Key words: octadecane, phase change, mixtures, OBC, heat conduction

摘要：

针对正十八烷相变易泄漏的问题，采用烯烃嵌段共聚物（olefin block copolymer，OBC）作为封装结构，制备复合定型相变材料。并通过添加膨胀石墨（expanded graphite，EG），改善其热导率低的问题。研究结果表明，当OBC的质量分数为20%时，复合相变材料未发现明显泄漏，定型效果较好，此时复合相变材料的相变焓为166.87 J/g，相较纯十八烷（227.40 J/g）下降26.62%。针对添加有不同质量分数EG的复合相变材料，其热导率随EG含量的增加而增大。其中当EG质量分数为5%时，复合相变材料热导率为4.179 W/(m?K)，较纯相变材料热导率[0.24 W/(m?K)提高了约16倍，即EG能够有效提高复合相变材料的导热性能。此外，5%含量下的复合相变材料相变焓约为149.54 J/g，且在经历50次循环后，相变温度和相变焓均未有明显变化，即制备的复合相变材料具有较好的热稳定性。因此，该复合相变材料在建筑节能方面具有应用潜力。

关键词: 正十八烷, 相变, 混合, 烯烃嵌段共聚物, 热传导