石墨纳米片尺寸对复合相变材料储热特性的影响

为了探究二维纳米材料的尺寸对复合相变材料储热特性的影响, 将膨胀石墨分别超声振荡10、30和90 min, 得到3种不同尺寸的石墨纳米片:GNS-10、GNS-30、GNS-90, 添加到十六醇中制备出纳米复合相变材料。利用SEM、XRD和Hot Disk等方法对其微观结构和性能进行表征和测试的同时, 对比研究了Maxwell、Bruggeman及Nielsen模型对热导率的计算结果。结果显示, 石墨纳米片尺寸越大, 对复合相变材料热导率的提升幅度越大。当GNS-10添加量为10%(质量分数)时, 热导率提升了约517%。Nielsen模型在形状因子A取100~180时可以较好地预测实验值。与大幅增长的热导率相比, 复合相变材料相变温度、相变焓的变化可忽略不计。此外, 石墨纳米片的加入明显缩短了储热材料的凝固速率, 有效热导率的提高是产生这种效果的主要原因。

Effects of graphite nanosheet size on thermal storage property of composite PCMs

In order to investigate the size effects of two-dimensional nanoparticles on the energy storage property of composite PCMs, graphite nanosheets (GNS-10, GNS-30, GNS-90) with different sizes were prepared by exfoliating expanded graphite with the assistance of ultra-sonication for different time and dispersed into hexadecanol. The prepared PCMs were characterized with SEM, XRD and Hot Disk, and the thermal conductivity was predicted by Maxwell, Bruggeman and Nielsen models. Results reveal that the graphite nanosheets presenting larger aspect ratios can achieve better thermal conductivity enhancement, because relatively large nanofiller contributes to the formation of heat transfer network in PCM matrix. An enhancement of thermal conductivity up to 517% has been achieved by GNS-10 at the loading of 10% (mass). The prediction of Nielsen model fits the experimental value better with the shape factor of A as 100 to 180. Compared to the great increase in thermal conductivity after the addition of graphite nanosheets, the changes in melting/solidification temperature and enthalpy of composite PCMs are negligible. Furthermore, the increased freezing rate of composited PCMs is clearly presented as a consequence of enhanced thermal conductivity.