气凝胶单元体模型结构参数与等效热导率研究

本文基于二氧化硅气凝胶的微观结构特点,运用小球构成的立方阵列单元体纳米孔隙模型,结合固相导热和气相传热的尺度效应,计算得到了一定尺寸范围内材料的等效热导率,分析了材料密度、颗粒接触面积、材料比表面积等因素对材料等效热导率的影响。结果表明:存在使气凝胶等效热导率取最小值的最佳密度;在一定的密度范围内,孔隙率一定时,材料的等效热导率随比表面积的增大而减小;颗粒间接触界面直径与固相颗粒直径的比值越大,等效热导率越低,在该比值一定时,气孔的尺寸和分布成为影响模型等效热导率的关键因素。

Relationship between Structure and Effective Thermal Conductivity of Silica Aerogel Unit Cell Model

In this paper,the regular cubic array of intersecting spheres is used as a unit model for silica aerogels.The effective thermal conductivity due to the solid and gas conduction with the microscale effect is analyzed with different model sizes.The results indicate that:there is an optimal density which results in the lowest effective thermal conductivity,the effective thermal conductivity decreases while the specific surface area and the contact area of the nanoparticles increase.When the contact area of the nanoparticles keeps constant,the pore size and distribution mainly affect the effective thermal conductivity of silica aerogels.