Thermal conductivity of nanoporous phenolic matrices: Measurements and predictions

Nanoporous phenolic-based composites are widely used as lightweight ablative thermal protection materials, but an accurate prediction of the effective thermal conductivity (aeff) associated with the nanoporous phenolic matrix (NPM) remains a significant challenge. Herein, a series of NPMs with different porosities are prepared, and their thermal conductivities measured experimentally. Precise nanostructure models for NPM are established by measuring the porous structural characteristics. These models have facilitated an accurate predication of aeff by combining the non-equilibrium molecular dynamics with the Lattice Boltzmann method, with an associated maximum deviation less than 5 %. Furthermore, the effects on aeff of intrinsic structure such as porosity, particle overlapping, pore and particle size, in addition to environmental factors are investigated. The results demonstrate that changes in aeff due to porosity are primarily confined to porosity values lower than 50 %. When the degree of particle overlapping is below 0.6, any increase in particle overlapping results in a marked increase in aeff. In addition, aeff exhibits a linear relationship with respect to temperature (below 673 K), and a response to changes in pressure is primarily observed within the range 104-107 Pa. This research provides significant insight into the thermal insulation characteristics and mechanisms of NPM, and can serve as a useful guide for the structural optimization of lightweight thermal protection materials.