超级绝热材料气凝胶的纳米孔结构与有效导热系数

Nano-porous structures and effective thermal conductivity of aerogel super insulator

根据气凝胶的纳米孔结构特点,采用由小球体构成的立方阵列单元体结构,建立了描述纳米孔超级绝热材料气凝胶的气固耦合导热模型。计算结果表明气凝胶的纳米孔结构和固体颗粒纳米尺寸效应以及高的比表面积值是导致材料具有极低导热系数的主要因素。气凝胶存在具有最低导热系数的最佳密度。在高温下辐射传热是气凝胶传热的主要方式。

Based on the open-cell nano-porous structure features, a cubic array of intersecting spheres unit cell model describing the coupled conduction of gas and solid in aerogel super insulator was developed. By one-dimensional heat conduction analysis in the unit cell, the effective thermal conductivity expression was obtained. The results show that the model is in agreement with experimental data and nano-porous structure, nanometer size effect of solids as well as the very high specific surface area are the key factors for the very low thermal conductivity. There exists an optimal density value where the thermal conductivity of aerogel is minimum. Thermal radiative heat transfer is the dominating heat transfer mechanism of aerogel at an elevated temperature. It can decrease the thermal conductivity value of aerogel effectively at high temperature by doping carbon or other matters which can strongly absorb infrared light at 3~8 μm.