Radiative characterisation of fibrous materials
Model medium consisting of randomly oriented and positioned internally
isotropic, infinitely long and optically large fibers of uniform diameter.
Radiative transfer is analyzed for participating media consisting
of long cylindrical fibers with a diameter in the limit of geometrical
optics (Fig. 1). 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 the fiber material. The fibers are assumed to be randomly oriented
and positioned inside the medium. Three approaches are employed:
a combined volume-averaging and Monte Carlo ray-tracing technique,
a combined mean-free path and Monte Carlo ray-tracing technique,
and an analytical approach recently developed for packed bed of spheres
and adapted here to long fibers.
The radiative properties obtained by the three methods are used to solve
to compute the overall transmittance and reflectance of the medium,
and the results are validated against predictions by the direct Monte Carlo
simulation. The effects of volume fraction and optical properties of fibers
on the medium radiative properties and the overall slab radiative
characteristics are investigated.