GAS-PERMEABILITY OF RIGID FIBROUS REFRACTORY INSULATIONS

An experimental procedure is developed for measuring the gas permeabil ity of rigid fibrous tile insulations. Permeability data are documente d for a variety of ceramic fiber insulations from the LI, AIM, FRCI, a nd AETB families, as well as for the commercial carbon fiber insulatio n FiberForm(R). It is demonstrated that rarefied-now effects are signi ficant for gas flow through such materials and that the pressure depen dence of gas permeability is well represented by the Klinkenberg formu lation. Continuum permeabilities ranging from 3 to 63 x 10(-12) m(2) a re found for all materials except FiberForm, which has a significantly higher continuum permeability on the order of 10(-10) m(2). The room temperature permeability slip parameter for air is found to range from 603 to 7940 Pa. A scaling relation that allows calculation of permeab ility slip parameters for other gases and for varying temperature is v alidated by experiment. The dependency of the permeability on material density, anisotropic microstructure, and constituent fiber size is pr esented. To illustrate an application of this permeability data, repre sentative computations for the gas now through a rigid fibrous vent of a space probe during launch and atmospheric entry are given.