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Effects of Convective Heat Transfer on Anisotropic Pyrolysis Propagation in a Porous Medium
Emilie Biotteau, Frédérick Plourde, Son Doan Kim and Jean-Pierre Lambelin

A bidimensional approach for heat and mass transfer modeling in a porous reactive medium is presented. This model is applied to pyrolysis of a square redwood sample exposed to high heat fluxes. As far as we know, this is the first time bidimensional pyrolysis mechanisms have been depicted through a three competitive reactions chemical model. The equation system presented is basic for modeling heat and mass transfer in porous media. But the set of differential and algebraic equations is discretized on a 2D grid to take into account the anisotropy of wood thermophysical properties. Internal temperatures, gas production rates and pressure in the porous matrix are presented. According to the results, pyrolysis propagates into the sample as time proceeds, and the reaction softens with this in-depth propagation. Paradoxically, the propagation rate is found to be faster across than along wood fibers whereas red-wood thermal conductivity is lower across the wood fibers. In fact, such propagation is due to the pressure field development with time in the sample, and it highlights convective heat losses along wood fibers.

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