HIGH-POROSITY metallic foams are being studied as possi-ble components of aerospace thermal protection systems. The performance of these systems needs to be characterized over a wide range of temperatures and pressures during ascent and reentry. 1 In the future, when such materials are specified as part of a vehicle program, part of the procurement process will involve certification that the material meets the specifications. To date there has been little research on experimental design for thermal characterization of high-porosity materials. The present research is intended to close this gap in the procurement cycle by investigating transient methods for accurate measurement of thermal properties in metal-foam materials. In this paper, only numerical simulations are presented.

A review of the pertinent literature is given next in the areas of optimal experimental design and heat transfer in high-porosity materials. Transient experiments combined with parameter estimation have been used for obtaining thermal properties for many years. 2 In these methods, the desired parameters are found by nonlinear regression between the experimental data (temperatures in this case) and a computational model of the experiment. Parameter estimation concepts have been applied to optimal experiment design for thermal characterization of uniform materials3 and for materials with temperature-varying properties. 4 One of the authors has previously studied optimal experimental design for the measurement of thermal conductivity in low-conductivity materials5 and in layered materials. 6 The work was limited to a small rise in temperature so that radiation heat transfer was negligible. An optimality criterion was used to find the best experimental conditions for the estimation of thermal properties.