Carbon preforms used in Thermal Protection System (TPS) materials are 80 to 90% porous, allowing for boundary layer and pyrolysis gases to flow through the porous regions. The bulk material properties such as permeability and hydraulic tortuosity factor affect the transport of the boundary layer gases. The use of Direct Simulation Monte Carlo along with the Klinkenberg permeability formulation allows us to compute the continuum permeability and Knudsen correction factor for flow in the transition regime. In this work, we have computed the permeability of two types of carbon preforms, namely, Morgan Felt and FiberForm, and assessed the effect of orientation of the permeability. It was found that for both the anisotropic materials, the permeability is higher in the in-plane orientation compared to the through-thickness orientation. Compared to Morgan Felt, FiberForm is less permeable, in both, through thickness and in-plane directions. The hydraulic tortuosity was higher for the FiberForm compared to Morgan Felt, and it was also found that the through-thickness orientation is more tortuous compared to the in-plane orientation.
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