Insight into structural-functional relationship for conductive-radiative heat transfer in multi-scale thermal insulating carbon aerogels

Abstract

The randomness in the porous structure of carbon aerogels makes them excellent thermal insulators. This study investigates heat transfer and structural-functional relationships in carbon aerogels. A database containing multi-scale structures derived from various experiments has been constructed, and a model that integrates molecular dynamics, lattice Boltzmann method, and discrete dipole approximation is proposed to explore cross-scale heat conduction and radiation. The results indicate that the density and medium-range order of microscale structures are critical factors influencing temperature-dependent thermal conductivities. The increase in thermal conductivity from 273 K to 1273 K is attributed to the excitation of vibrations with frequencies exceeding 16 THz. For aerogels characterized by low medium-range order atomic structures, thermal conductivity rises at temperatures above 1673 K due to further graphitization. Mesoporosity emerges as the primary determinant of aerogel thermal conductivity at the mesoscale, exhibiting an approximately linear relationship with thermal conductivity. Despite high temperatures, radiation remains a minor contributor to heat transfer. Regulating aerogel structures based on differential influences of multi-scale porosity can effectively reduce their thermal conductivities. For lowly graphitized aerogels, this involves decreasing microscale density, while for highly graphitized aerogels, controlling their microscale density under 1.6 g·cm⁻³ can suppress the medium-range order of carbon atoms.