The nanoporous aerogel materials exhibit a unique combination of properties including high porosity, low density and excellent thermal insulation performance which have great potential for application as super thermal insulation materials and other fields. Characterizing the complicated structure and exploring the thermal transport mechanism is a significant important and challenge work.
The phonon energy transfer of solid backbone and gas molecule conduction are discussed and the solid-gas coupling heat transfer of both the local solid-gas interaction and the thermal-bridge interaction are explored. 
Infrared opacifiers and reinforcements are usually doped in aerogels to improve its insulating capability at high temperature. The optimal temperature-dependent size and temperature-dependent doping amount is determined by considering the combined conduction and radiation thermal transport properties. Novel types of multi-layer graded doping scheme are designed and the insulating capability is improved effectively. In particular, non-silica fiber doping satisfying both heat transfer and mechanical requirements in harsh thermal environment are investigated in details, and for the first time, we propose a stratified design for oxidizable carbon fiber to extend its excellent radiation suppression capacity to extra-high temperature. This work was supported by the National Natural Science Foundation of China under grant numbers of 51825604 and 51721004.