ISOLATING THE MODES OF HEAT TRANSFER IN FIBROUS INSULATION MATERIALS

Thermal protection systems (TPS) are used in reentry vehicles due to the extreme thermal environments experienced during reentry. Porous, fibrous insulation materials are commonly used in TPS. Heat is transferred by three primary modes of heat transfer in fibrous insulation materials: solid conduction, gaseous conduction, and radiation. Solid conduction occurs due to the fibers in the TPS fiber matrix. Gaseous conduction is due to the gases present in the pores of the fiber matrix. Finally, radiation is emitted from the fibers and absorbed and scattered throughout the fiber matrix. It is of importance that these modes of heat transfer can be accurately modeled so that an efficient and satisfactory TPS can be developed. An experimental apparatus utilizing the comparative cut bar method has been developed to measure the thermal conductivity and isolate these modes of heat transfer in fibrous insulation materials. Previously, the modes of heat transfer have been isolated by first determining the contribution from gaseous conduction by testing over a range of pressures. Solid conduction and radiation were then isolated using genetic algorithms. This requires testing over a wide range of temperatures. This work looks at isolating all three modes of heat transfer at once so testing at only one pressure is required. Testing has also been conducted on FiberForm^®and the effective thermal conductivity fits from applying genetic algorithms are presented.