Determination of thermal-physical characteristics of thermal materials at high temperatures

Abstract

This study presents an experimental–numerical method for determining the thermal conductivity and heat capacity of thermal insulation materials (TIM) at elevated temperatures. The derived thermophysical characteristics were compared with the known properties of the analogous materials. Two TIMs ZYF-150 and NAB (manufacturer: ZIRCAR Ceramics, Inc., USA), were investigated in this study. Both materials exhibit a fibrous, highly porous structure reminiscent of felt, allowing them to easily conform to a given volume and shape. In ZYF-150, the fibers are composed of zirconium dioxide (ZrO₂) stabilized with yttrium oxide (Y₂O₃), whereas NAB consists of aluminum oxide (Al₂O₃) fibers containing silicon dioxide (SiO₂) impurities. In the experiments, the samples were heated using a propane–oxygen torch operating in a reducing flame mode, with the use of a carbon–carbon composite interlayer. This prevented any direct mechanical impact of the flame on the sample surface while ensuring efficient conductive heat transfer. Finite element simulations of the heating process were performed using COMSOL Multiphysics®. The experimentally obtained surface temperature measurements were applied as boundary conditions to solve the inverse heat conduction problem. Consequently, the temperature dependencies of the thermal conductivity coefficients for the ZYF-150 and NAB materials were established. For the NAB material (λ_NAB5), the root-mean-square deviation was 15.5% with a maximum relative error of 23.6%, whereas these values were 21.5% and 44% for ZYF-150. The comparative analysis of the thermophysical properties of the investigated materials with those of similar materials confirms the validity of the developed methodology. The obtained results are expected to be useful for material scientists working on thermal protection materials and for the design of thermal protection systems based on them.