(178e) Three-Dimensional Microscale Numerical Simulation of Smoldering | AIChE

(178e) Three-Dimensional Microscale Numerical Simulation of Smoldering



A three-dimensional numerical tool for the simulation of smoldering in fixed beds of solid fuels is presented in this paper. The description is based on the microscale equations, in a detailed discretized image of the porous medium. Simplifying assumptions are used, but the local coupling of the transport and reaction mechanisms is fully preserved. A first set of 2D and 3D simulations demonstrates the ability of the model to handle a variety of situations, and to provide detailed local information. In particular, it is shown that severe thermal disequilibrium exists in some regimes, which preclude a straightforward application of simple macroscopic models. A macroscopic point of view is adopted in most theoretical studies, whereby the medium is regarded as a continuum. The equations usually involve effective parameters such as dispersion coefficients or mean volumetric reaction rates, and they relate macroscopic fields that represent volume averaged local quantities. However, the effective coefficients depend on the medium microstructure and on the flow and reaction regimes, and their determination generally requires the solution of the full set of microscale equations in a representative sample. In addition, the validity of homogenized equations is also questionable, in view of the strong gradients on the microscopic scale. Finally, local non-equilibrium plays an important role in many respects, such as in pollutant formation, and it can only be modeled by detailed local simulations at the microscale level. A first set of microscale simulations reproducing known macroscopic regimes described in [1] were presented in the review paper [2] using the local microscale model presented in [3]. The aim of this paper is to show the ability of this code to treat solid combustion in 3D heterogeneous porous media such as oil shale and to clearly exhibit the disequilibrium existing in temperature fields at the local scale which is a situation difficult to reproduce using an homogeneized description.

1. Aldushin, A.P., Rumanov, I.E. and Matkwosky, B.J., Combust. Flame 50:76-90 (1999).

2. Debenest G., V.V. Mourzenko, J.-F. Thovert, Combust. Theory Modelling, 9:113-135 (2005).

3. Debenest G., V.V. Mourzenko, J.-F. Thovert, Combust. Theory Modelling, 9;301-321 (2005).

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