Experimental Study On Measuring Thermal Conductivity Of Carbonizing Composites

Carbonizing composites have been wide used in thermal protection system of various space vehicles. It is very important to study the thermal physical parameters. Thermal conductivity of carbonizing composites directly affects temperature distribution inside the thermal protection layer, so it is the key parameter in design the thickness of TPS.Thermal decomposition appears makes it difficulty to describe the course of heat transfer inside carbonizing composites, and it is more difficulty to determine the thermal conductivity. The thermal conductivity attained with traditional method by ignoring thermal decomposition, so it has some difference with the thermal conductivity of carbonizing composites used. It is very necessary to develop an experimental method to measure the thermal conductivity of carbonizing composites under aero-heating.By analyzing the physical model of carbonizing composites under aero-heating, the mathematical model with thermal decomposition has been found. The relational parameters during thermal decomposition, includingρ_∞-density of material at terminaldecomposition, k₀e^-E/(RT)-reaction rate constant for reaction of thermal decompositionand AH -heat of reaction of thermal decomposition are measured by tests.In order to simulate the aero-heating environment, different arc heaters were used, subsonic nozzle, supersonic nozzle and models etc were designed. When surface temperature within 1000K-2000K, the flat plate models have been experimented on the subsonic jet stream apparatus with arc heater. When surface temperature close to 3500K, the cylinder models have been experimented on the supersonic jet stream apparatus with arc heater. The temperatures on surface and inside the models have been recorded. For models which surface temperature close to 3500K, the ablation recession rate have been measured.The initial, boundary and additional conditions are used. The thermal conductivity has been gained by resolving the heat conduction equation. The effects on result due to thermal decomposition, measuring error and different physical models are analyzed and discussed.