Multi-scale Modeling of Radiation Heat Transfer through Nanoporous Superinsulating Materials

In this contribution, the extraordinarily high level of thermal insulation produced by nanoporous materials, which can achieve thermal conductivities down to a few mW·m⁻¹·K⁻¹ when they are evacuated to a primary vacuum, is highlighted. The objective here is to quantify the level of radiation heat transfer traveling through a nanoporous material in relation with its composition. The model used here is based on the “non-gray anisotropically scattering Rosseland approximation,” which allows the definition of a “radiation thermal conductivity” expressed as a function of the optical properties (complex optical index spectra), mean sizes and volume fractions of the different populations of particles constituting the material. With the help of this simple model, one can draw interesting conclusions concerning the impacts of different parameters related to the microstructure of the nanoporous material on the amplitude of the radiation heat transfer. In the future, this model should help to orient the formulation of new nanoporous materials with optimized radiative properties.