Numerical and experimental characterization of high-temperature heat transfer in a ceramic foam with dual-scale porosity

Abstract

In this paper, we compare numerical predictions and measurements of the high-temperature apparent thermal conductivity of an insulating alumina foam with dual-scale porosity: the foam contains ▪-sized cells and also ▪-sized pores in the highly scattering foam skeleton. Simulations of the apparent thermal conductivity are performed on tomography-reconstructed foams, with a three-part multi-scale approach to account for the dual-scale porosity. The effective phonon thermal conductivity of the foam is first computed using a finite element homogenization technique. The spectral and temperature-dependent effective radiative properties of the foam are next computed through an improved Monte Carlo ray-tracing approach, with foam skeleton scattering modeled using a physical-optics-based approach. The apparent thermal conductivity of the foam is then simulated by resolving the coupled conductive-radiative heat transfer through a semi-infinite homogeneous slab. The simulated high-temperature apparent thermal conductivity is found to be in good agreement with experimental data up to ▪, obtained by parallel hot wire measurements coupled with an improved quadrupolar model for low-density insulating materials. The large influence of scattering at the cell-skeleton interface is shown through a numerical parametric study. It is also shown that the Rosseland conductivity calculated directly from the simulated spectral radiative properties provides a good estimation of radiative heat transfer for optical thicknesses exceeding 30.