Permeability of Space Vehicle Fibrous Thermal Protection Blankets in Viscous and Slip Flow Regimes

Abstract

The permeability of thermal protection blankets is measured by flowing air and helium at pressure differentials of up to 33.3 kPa across the material. Flow in both the viscous and slip regime is demonstrated by varying the average absolute pressures in the experiments from 0.400 to 80.0 kPa. Analysis shows the flow through the fibrous blanket is well characterized by a compressible formulation of Darcy’s law with the addition of the Klinkenberg slip factor. The permeability and slip parameter are obtained using multiple linear regression. A comparison between air and helium shows that the slip parameter scales with the square root of the molecular weight. Correlations between the permeability and slip factor for fibrous materials are proposed. The correlations are similar in form with previous correlations developed for rock samples, but the coefficients differ. The measured data show that the capillary radius calculated from permeability is the appropriate length scale for the Knudsen number.