Discrete vs Continuum Level Simulation of Radiative Transfer in Semitransparent Two-Phase Media

Abstract

a b s t r a c tThe mathematical formulation of the continuum approach to radiative transfer modeling in two-phase semi-transparent media is numerically validated by comparing radiative fluxes computed by (i) direct, discrete-scale and (ii) continuum-scale approaches. The analysis is based on geometrical optics. The discrete-scale approach uses the Monte Carlo ray-tracing applied directly to real 3D geometry measured by computed tomography. The continuum-scale approach is based on a set of continuumscale radiative transfer equations and associated radiative properties, and employs the Monte Carlo ray-tracing for computations of radiative fluxes and for computations of the radiative properties. The model two-phase media are reticulate porous ceramics and a particle packed bed, each composed of semitransparent solid and fluid phases. The results obtained by the two approaches are in good agreement within the limits of statistical uncertainty. The continuum-scale approach leads to a reduction in computational time by approximately one order of magnitude, and is therefore suited to treat radiative transfer problems in two-phase media in a wide range of engineering applications.Published by Elsevier Ltd.

Radiative characterization of random fibrous media with long cylindrical fibers: Comparison of single- and multi-RTE approaches

“…Note that none of the methodologies is new. The multi-RTE approach has been initiated by Consalvi et al [12] and developed by Lipinski et al [13,14] . This method was derived by applying the volume averaging theorem by Whitaker and Quintard [39] to the multicomponent media.…”

“…The number of rays over cross-sectional area in the forward and backward directions and the number of rays leaving the slab from the inlet and the outlet, are again used to compute the radiative flux, reflectance and transmittance through Eqs. (11) - (14) . More details about the DSMC to simulate light propagation in slabs of optically large fibers with random orientation can be found elsewhere.…”

“…The collision-based Monte Carlo ray-tracing method (MCRT) is used in combination with radiative distribution functions for semitransparent media [7,14,17,36] . A large number of stochastic rays N distributed within REV of the fibrous samples are emitted.…”

“…A theoretical multi-RTE approach, i.e. averaged radiative transfer equations are valid in each individual phase, has recently been introduced within the limit of geometrical optics assumptions [12][13][14][15][16][17][18] . This approach has the ability to incorporate realistic and morphologically complex media.…”

“…[6,[34][35][36] ), foams (e.g. [14,18] ) and fibrous media, [33] in order to estimate the applicability of simplifying theoretical approaches for predicting radiative transfer in isotropic fibrous materials consisting of optically large fibers. Two approaches are employed: (1) a volume-averaging approach for the calculation of averaged intensities in the multiple phases, referred to as multi-RTE approach , and (2) a single intensity approach, referred to as single-RTE approach .…”