An inverse analysis to estimate the endothermic reaction parameters and physical properties of aerogel insulating material

Silica aerogel is a kind of highly nano-porous material with excellent performance in heat insulation. Some researches showed that during the heating process, some kind of reactions happened inside the material accompanying with endothermic/exothermic phenomenon, such as evaporation of water or residual solvent. These reactions will greatly change the properties of the material as well as affect its insulation performance at high temperatures. Therefore, it is crucial for silica aerogel insulating material to understand its transient heat transfer characteristics and to identify the thermal properties as well as some other key parameters. In this study, a numerical heat transfer model is constructed to study the transient heat transfer characteristics of the aerogel material in which the reaction effect is taken into account. Finite volume method combined with Enthalpy method are used to numerically solve the heat transfer problem. In order to determine the key parameters of the heat transfer model, an inverse analysis is conducted based on the Levenberg-Marquardt method. Through the inverse analysis technique, parameters such as thermal conductivities before and after the reaction, λ_virgin and λ_reacted, reaction temperature T_reaction and reaction heat L, can be estimated by using a group of experimentally measured temperature history curves. Besides, sensitivity analysis as well as the influence of measurement errors are also discussed. The results show that (1) The optimum values for these parameters which are consistent with the actual situation are X_u⁰ = (λ_virgin, λ_reacted, T_reaction, L) = (0.1380 W/(m·K), 0.0535 W/(m·K), 355.45 K, 230,670 (J/kg)); (2) The accompanying thermal effect of the reaction heat is small and can be neglected. The main effect of reaction on the heat transfer characteristics is due to the change of the component of the material. The component change of material will then lead to the variation of thermal properties which greatly affect the heat transfer process.