Heat Transfer in Fibrous Insulations: Comparison of Theory and Experiment

Abstract

The validity of an improved theoretical model for radiative heat transfer through high-porosity e ber insulation is examined by comparison of experimental measurements with theoretical predictions of heat transfer. Radiative thermal conductivity of an optically thick medium is modeled by a diffusion approximation in which the spectral extinction properties are calculated by utilizing a rigorous treatment of the e ber medium scattering phase function and the composition of the e ber material. A semiempirical model is used to calculate the e ber-matrix conduction. The accuracy of the model is tested by comparison with experimental heat transfer data measured in vacuum for temperatures from 400 to 1500 K for three types of bonded silica e ber thermal insulation materials having different e ber size distributions. The validity of the modeling approach is demonstrated by the excellent agreement between the theoretical predictions and the experimental results.