A model of wood logs combustion for CFD simulations

In this study a relatively simple, quasi steady, heterogeneous reaction model to be used in CFD computer codes is presented. It is suited for the simulation of the coupled solid and gas-phase reactive environment when at a specific stage of the combustion of wood logs. The wood degradation is described adopting a quasi-steady assumption for the solid phase. Pyrolysis and char gasification are described by a set of four surface reactions. A detailed description of the solid matrix is avoided while the interaction trough heat and mass transfer between the two phases is still retained. Wood is defined as a species with chemical composition equivalent to real wood in terms of the principal elements: Carbon, Hydrogen and Oxygen in such a proportion to include the moisture content. The wood degradation is modelled using an apparent surface kinetic controlled by temperature only to produce char and volatiles. The gas phase is modelled as a turbulent flow (RANS approach) with the turbulence-reaction interaction described with the Eddy Dissipation Concept and a four steps chemical mechanism. Model validation is provided by comparison with published results obtained with a more complex model for the devolatilization of wood [1].