THE CALCULATION OF ANISOTROPIC EXTINCTION COEFFICIENTS FOR RADIATION DIFFUSION IN RIGID FIBROUS CERAMIC INSULATIONS

The specific anisotropic extinction coefficient e couples the effecti ve radiative properties of a fibrous insulation into the radiation dif fusion equation. This coefficient can be calculated using electromagne tic scattering theory if fiber diameters, refractive indices and fiber orientation distributions are known. In general, fiber orientation di stributions are not readily accessible and past calculations have cons idered fibers as either randomly distributed or normal to the heat flo w direction. In certain rigid fibrous ceramic insulations neither of t hese cases apply well, and a simple procedure is described for approxi mating e from values calculated for the random and normal orientation cases. The intrinsic error associated with this scaling procedure is investigated. Numerical computations for several test structures and f iber materials show the average error to be less than 5% for net heat flux and radiation conductivity calculations. Published by Elsevier Sc ience Ltd.