A generic local thermal equilibrium model for porous reactive materials submitted to high temperatures

Abstract

Many engineering applications involve reacting porous materials submitted to high temperatures. This work presents a detailed but pragmatic heat and mass transfer model for porous materials containing several solid phases and a single gas phase. The detailed chemical interactions occurring between the solid phases and the gas phase are modeled at the pore scale assuming local thermal equilibrium. Homogenized models are obtained for solid pyrolysis, pyrolysis species injection in the gas phase, heterogeneous reactions between the solid phases and the gas phase, and homogeneous reactions in the gas phase. The chemistry models are integrated in a macroscopic model making use of volume-averaged governing equations for the conservation of solid mass, gas mass, species (finite-rate chemistry) or elements (equilibrium chemistry), momentum, and energy. The model has been implemented in the Porous Material Analysis Toolbox based on OpenFoam (PATO), distributed Open Source by NASA. Applications to two high-temperature engineering problems are presented. The first application concerns the design of heat-shields of space vehicles. The second one aims at improving the understanding of biomass pyrolysis for the production of biohydrocarbons.