Simulation of Thermal Response of Ultralight Porous Ablative Insulators Based on Carbon Aerogels

Hypothesis: In recent years, porous carbon-phenolic ablators have attracted attention for special aerospace missions due to the capability of the structural and density tuning to achieve a balance between ablation and insulation performance under thermal-aerodynamic conditions. Phenolic resin-impregnated carbon aerogels with a three-dimensional, interconnected nanoporous network structure, very low density, and special insulation properties are a novel type of lightweight carbon-phenolic ablators. Also, the development of mathematical models and simulation of thermal response of ablative insulators, appropriate to their structure is carried out with the aim of predicting the temperature and density distribution in the ablator depth. The theoretical results ultimately lead to the determination of the optimal insulation thickness for the application conditions
Methods: Novel types of ultralight carbon-phenolic composites based on carbon aerogels with low density in the range of 0.36 to 0.76 g/mL were fabricated. After defining a mathematical model to predict the temperature distribution and depth density of the ablators, the model input data such as thermal degradation kinetic parameters and thermophysical properties were estimated using TGA and recession rate analysis. Also, the microstructure of the ablator material was investigated using scanning electron microscopy during the ablation process. Then, the ablation process of the prepared thermal insulators was simulated using the commercial software Comsol Multiphysics based on the 1-D mathematical model.
Findings: The results showed that increasing the density of the ablator from 0.36 to 0.76 g/mL helped to decrease the surface and the depth temperatures of the ablator The depth temperature of the ablators with a density of 0.36 g/cm3 at the depth of 25 and 35 mm was 100°C and 65°C, respectively. The in-depth temperatures decreased  80°C at 25 mm and 58°C at 35 mm) for the ablator with the density of 0.76 g/mL. The surface recession rate also decreased from 0.091 to 0.055 mm/s with the density increase. Lightening of the ablators caused the occurrence of the in-depth ablation phenomenon, while for the ablators with higher density, pyrolysis and ablation occurred in the surface region. Comparison of simulation and experimental results indicated that the thermal behavior of phenolic impregnated carbon aerogel ablators was predicted favorably using the developed computer program. Using the developed computer program, the ablator density and the required thickness of thermal insulator could be estimated for each application condition.