Abstract
Modelling of packed-bed combustion includes the problem of modelling the radiative heat transfer. Thermal radiation significantly contributes to heat transfer both across the bed and from the hot gases to the top of the fuel layer. Several methods can be utilized aside from the so-called effective bed conductivity, such as the P1 or the Discrete Ordinates Model. When using the porous media for the fuel representation, its effective radiative properties must be determined, namely the extinction coefficient Gómez et al. (2014). It is often determined by assuming regularly oriented and mono-sized particles Shin and Choi (2000). Expressions for its estimation differ in the quantity representing the fuel and bed properties, for example, the bed porosity or particle emissivity. However, the absorption and scattering are influenced not only by how densely the particles are packed but also by their mutual position and orientation. The estimated radiative properties can significantly influence the combustion simulation, both quantitatively (e.g., the thickness of the reaction front, and ratios of the produced gases) and qualitatively (ignition of the fuel or the flame extinction). This work compares expressions of the radiative properties, that are modified by introducing irregularities in the positions or orientation of the fuel particles. The model for the radiative properties is implemented as a part of the radiation model based on the Discrete Ordinates method, modified for the case of two Eulerian phases representing the fuel and gas phase. In the presented work, these models for radiative properties are compared in a case of a fixed-bed reactor described by Zhou et al. (2005) and compared to the reported experimental results. The case is modelled in two dimensions. The radiation model is also described, including its implementation in ANSYS Fluent.
