二氧化硅气凝胶的等效热导率理论

应用分子运动论对二氧化硅气凝胶的传热机理进行了研究。根据其微观结构特点,建立了纳米孔隙模型。考虑气体分子间的相互作用力,推导了纳米孔隙内气体的热导率,得到了二氧化硅气凝胶内气体热导率的表达式。建立了二氧化硅气凝胶固相结构单元导热模型,运用分子运动论推导了固相结构的热导率,获得了二氧化硅气凝胶的总体等效热导率。结果表明,影响二氧化硅气凝胶内气体热导率的主要因素是气体的平均分子自由程与分子之间以及分子与壁面之间的相互作用,固相结构单元的直径和接触界面的直径是影响固相结构单元热导率的主要因素,而二氧化硅气凝胶孔隙尺寸的分布严重影响其等效热导率。

TheoreticalResearchonEffectiveThermalConductivityofSilicaAeroge

The heat transfer mechanism of silica aerogel was studied by using the kinetic theory. Based on the features of the microstructure of silica aerogel, nanopore model was built. The expression of the thermal conductivity of gas in nanopore was derived with taking account of the interaction force of molecules. The thermal conductivity of gas in silica aerogel was achieved with the derived expression. A heat transfer model of solid matrix unit obtained from the structure of silica aerogel was developed. According to the kinetic theory, the effective thermal conductivity of silica aerogel was obtained. The results show that the average gas molecule free path, the interaction force of molecules and the force between molecule and wall are the major factors which effect the thermal conductivity of gas in silica aerogel, the diameters of solid matrix unit and contact interface are main factors affecting the thermal conductivity of solid matrix unit, the pore size distribution seriously affects the equivalent thermal conductivity of silica aerogel.