HEAT-TRANSFER IN FIBROUS INSULATIONS - COMPARISON OF THEORY AND EXPERIMENT

The validity of an improved theoretical model for radiative heat trans fer through high-porosity fiber insulation is examined by comparison o f experimental measurements with theoretical predictions of heat trans fer. Radiative thermal conductivity of an optically thick medium is mo deled by a diffusion approximation in which the spectral extinction pr operties are calculated by utilizing a rigorous treatment of the fiber medium scattering phase function and the composition of the fiber mat erial. A semiempirical model is used to calculate the fiber-matrix con duction. The accuracy of the model is tested by comparison with experi mental heat transfer data measured in vacuum for temperatures from 400 to 1500 K for three types of bonded silica fiber thermal insulation m aterials having different fiber size distributions. The validity of th e modeling approach is demonstrated by the excellent agreement between the theoretical predictions and the experimental results.