Heat transfer in high-temperature fibrous insulation

The combined radiation/conduction heat transfer in high-porosity, high-temperature fibrous insulations was investigated experimentally and numerically. The effective thermal conductivity of fibrous insulation samples with densities of 24-72 kg/m(3) and thicknesses of 13.3-39.9 mm was measured over the temperature range of 3001300 K and environmental pressure range of 1.33 x 10(-5)-101.32 kPa. It was experimentally determined that for the fibrous insulation densities and thicknesses investigated no heat transfer takes place through natural convection. A finite volume numerical model was developed to solve the governing combined radiation and conduction heat-transfer equations. The radiation heat transfer was modeled using the modified two-flux approximation assuming anisotropic scattering and gray medium. A genetic-algorithm-based parameter estimation technique was used in conjunction with a subset of steady-state effective thermal conductivity measurements to determine the relevant conductive and radiative properties of the fibrous insulation. The numerical model was verified by comparison with steady-state effective thermal conductivity measurements and a transient thermal test simulating reentry aerodynamic heating conditions.