Geometric optimization of aerogel composites for high temperature thermal insulation applications

•An optimization method is developed to design aerogel composites with low thermal conductivity.•Both volume fraction and size of micro-scale opacifiers and fibers are optimized.•Optimized density of silica aerogel matrix is mainly in the range of 130-200 kg/m3.•Low thermal conductivity additives are preferred when temperature is < 600 K.•Additives with a broad size distribution are preferred when temperature varies. Silica aerogel has attracted great interest in thermal insulation applications due to its ultralow thermal conductivity. However, silica aerogel is transparent to the infrared radiation in the range of 3-8 µm, making them be not suitable for high temperature thermal insulation applications. Here, we developed an optimization method considering both thermal radiation and heat conduction to design the geometric structures of aerogel composites with minimized thermal conductivity. The results show that when the ambient temperature is lower than ~ 600 K, the additives with low thermal conductivity are preferred. When the ambient temperature is higher than ~ 600 K, the additives with high extinction coefficients are needed. The additives with a broad size distribution could enable the aerogel composites to have an optimal thermal insulation performance in the environment with a changing temperature. The work provides a guideline for the geometric design of aerogel composites for high temperature thermal insulation applications.