An Orthotropic Thermal Conductivity Measurement in Flexible, Fibrous Insulation Materials

A testing apparatus has been developed to help characterize the thermal conductivity of fibrous insulation materials. The goal of this apparatus is to measure the in-plane thermal conductivity of thermal protection systems (TPS) materials along with the through-the-thickness thermal conductivity. Previous experiments have focused on characterizing and modeling the through-the-thickness thermal conductivity of TPS materials. Very few experiments, if any, have characterized and modeled the in-plane thermal conductivity as a function of temperature, pressure, and gaseous composition. The in-plane thermal conductivity of fibrous insulation materials such as PICA or its substrate FiberForm^® is estimated to be 2–3 times higher than their respective through-the-thickness thermal conductivities. Due to this difference, the in-plane thermal conductivity plays an important role in determining how incident heat fluxes are spread out along re-entry vehicles. The through-the-thickness and in-plane thermal conductivity of Pyrogel XTE, or Aerogel, was measured. It was found that the through-the-thickness thermal conductivity was 0.060 W/mK and the in-plane thermal conductivity was 0.265 W/mK.