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Modeling Study of Pyrolysis of Composite Materials : Application to Wood and Carbon/Epoxy Composite

Abstract : Composite materials occupy a critical position in industrial applications or more broadly in our daily life. Synthetic composites substitute metallic materials due to their lightweight properties to achieve identical mechanical performance. They are widely used in the fields of energy transportation and storage. Natural composites (wood) are also widely used, especially in construction industry. The disadvantage of these materials involves the disability in maintaining their mechanical characteristics in a fire scenario, and the study of their fire resistance is therefore a major issue. This thesis aims to develop a mathematical model of thermal decomposition of composite materials subjected to different heating conditions. The simulations of different cases of thermal decomposition make it possible to study the interactions among the processes of heat and mass transfer as well as chemical reactions within the solid. The developed 3D model describes the gas transport within the pores of materials at the Darcy scale. Thermal conductivity is formulated in a tensor form allowing the definition of heat transfer in three directions of the domain. For the two types of materials, a multi-step reaction scheme is defined to describe the pyrolysis process. The cone calorimeter tests used to validate the model were carried out under an inert atmosphere (Nitrogen) which makes it possible to eliminate the presence of flame on the material surface as well as the heterogeneous reactions which can occur in the presence of oxygen. Therefore, the defined boundary conditions are quite simple and well-controlled to characterize without considering the unsteady flame. Pyrolysis gasses are assembled into inert gas, therefore, the gas reactions in the pore are neglected and the local thermal equilibrium between the solid and gas phase is assumed. The implementation of this pyrolysis model follows a scale separation process with two types of materials. The different heat and mass transfer processes, as well as chemical reactions, are studied separately to avoid the interactions, then the model is reconstructed to take these interactions into account. The pyrolysis behavior is firstly studied at a "0D" scale to develop the part of chemical reactions. The thermogravimetric analysis (TGA) is used at this scale and related experiments are conducted at different heating rates under an inert atmosphere. At this scale, only the chemical reactions are involved with known kinetics, and the heat and mass transport within the solid can be neglected with homogeneous temperature distribution. The different chemical reactions are described with the Arrhenius-type equation. The kinetic parameters are calculated by the inverse modeling method. The influence of the heating rate on the pyrolysis process is analyzed and 2D simulations are conducted at two heating rates to analyze the evolution of thermal and pressure gradients within the solid. The phenomena of heat and mass transport are considered and studied by bench-scale experiments which are conducted in the cone calorimeter. The corresponding simulations are implemented under two heat flux. The interactions among the heat and mass transport as well as chemical reaction processes are studied by analyzing the local time and length scales to identify what are the dominant phenomena through the whole pyrolysis process.
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Submitted on : Friday, March 12, 2021 - 11:00:37 AM
Last modification on : Wednesday, October 20, 2021 - 3:22:15 AM
Long-term archiving on: : Sunday, June 13, 2021 - 6:38:39 PM


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  • HAL Id : tel-03167564, version 1




Xiaowen Qin. Modeling Study of Pyrolysis of Composite Materials : Application to Wood and Carbon/Epoxy Composite. Other. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2021. English. ⟨NNT : 2021ESMA0006⟩. ⟨tel-03167564⟩



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