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

Abstract

a b s t r a c tRadiative heat transfer is analyzed in participating media consisting of long cylindrical fibers with a diameter in the limit of geometrical optics. The absorption and scattering coefficients and the scattering phase function of the medium are determined based on the discrete-level medium geometry and optical properties of individual fibers. The fibers are assumed to be randomly oriented and positioned inside the medium. Two approaches are employed: a volume-averaged two-intensity approach referred to as multi-RTE approach and a homogenized single-intensity approach referred to as the single-RTE approach . Both approaches require effective properties, determined using direct Monte Carlo ray tracing techniques. The macroscopic radiative transfer equations (for single intensity or two volume-averaged intensities) with the corresponding effective properties are solved using Monte Carlo techniques and allow for the determination of the radiative flux distribution as well as overall transmittance and reflectance of the medium. The results are compared against predictions by the direct Monte Carlo simulation on the exact morphology. The effects of fiber volume fraction and optical properties on the effective radiative properties and the overall slab radiative characteristics are investigated. The single-RTE approach gives accurate predictions for high porosity fibrous media (porosity about 95%). The multi-RTE approach is recommended for isotropic fibrous media with porosity in the range of 79 −95%.

Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

“…On the other hand, the use of fibrous pellets offering high porosity for rapid reaction rates and facilitated integration can be a relevant option to operate packed-bed solar reactors, provided that uniform heating can be effectively reached [39]. In this application, the actual density of the pellets combined with their regular shape results in a bulk density inside the reactor chamber that allows reaching the desired theoretical ideal mass of ceria in the reactor (i.e.…”

Continuum approach based on radiation distribution function for radiative heat transfer in densely packed particulate system

“…Lipinski et al [33,34] developed a multiphase radiative transfer theory based on the spatial averaging theorem for multiphase heterogeneous media. Randrianalisoa et al [35] compared the classic RTE and multiphase RTE approaches in the random fiber media and obtained the scope of application of these two approaches.…”

Thermal emission from a single glass fiber

“…It is worth noting that the Rosseland analytical expression of the radiative conductivity of a gray optically thick medium [10] is used by default for a fibrous galss assembly [1,3]. In most of the works reported to date, the radiative heat transfer through a fibrous assembly or its radiative properties are investigated by solving the radiative transfer equation (RTE) [11][12][13][14][15][16]. In this work, we will focus on the thermal radiation from a single glass fiber.…”