Measurement and identification of temperature-dependent thermal conductivity for thermal insulation materials under large temperature difference

Thermal insulation materials are widely used in the fields of thermal protection and the energy conservation at high temperature. Thermal conductivity is one of the most important parameters of characterizing the thermal insulation performance of thermal protection materials. Steady state method such as the guarded hot plate method is normally considered as the most accurate method to measure the thermal conductivity of thermal insulation materials, but the temperature range is limited to below 1000 K. Unsteady state method can be employed at higher temperature but the accuracy is lacking of validation. Consequently, thermal verification experiments are usually conducted by heating the front surface of thermal insulation materials to a very high temperature. However, it is difficult to obtain the temperature-dependent thermal conductivity by using the thermal insulation performance measured with a large temperature difference across the material. In this study, a sandwich structure experimental system is built to carry out the thermal insulation performance tests with a large temperature difference at both steady state and transient state. Both uniform temperature layer method and polynomial fitting method are adopted to extract the temperature-dependent thermal conductivity from the large temperature difference test at steady state. A new transient state identification method is proposed based on the niche genetic algorithm to identify the relation between thermal conductivity and temperature from the transient thermal response. The temperature-dependent thermal conductivity of four thermal protection materials are finally obtained. The identification results prove that the proposed transient identification method is reliable and robust.