Tl. Farias et al., COMPUTATIONAL EVALUATION OF APPROXIMATE RAYLEIGH-DEBYE-GANS FRACTAL-AGGREGATE THEORY FOR THE ABSORPTION AND SCATTERING PROPERTIES OF SOOT/, Journal of heat transfer, 117(1), 1995, pp. 152-159
A computational evaluation of an approximate theory for the optical pr
operties of soot is described, emphasizing the small-angle (Guinier) r
egime. The approximate theory (denoted RDG-FA theory) is based on the
Rayleigh-Debye-Gans scattering approximation while treating soot as ma
ss-fractal aggregates of spherical primary particles that have constan
t diameters and refractive indices. The approximate theory was evaluat
ed by more exact predictions from the solution of the volume integral
equation formulation of the governing equations, ruing the method of m
oments, and based on the ICP algorithm of Iskander et al. (1989). Nume
rical simulations were used to construct statistically significant pop
ulations of soot aggregates having appropriate fractal properties and
prescribed numbers of primary particles per aggregate. Optical propert
ies considered included absorption, differential scattering, and total
scattering cross sections for conditions typical of soot within flame
environments at wavelengths in the visible and the infrared Specific
ranges of aggregate properties were as follows: primary particle optic
al size parameters up to 0.4, numbers of primary particles per aggrega
te up to 512, mean fractal dimensions of 1.75, mean fractal prefactors
of 8.0, nod refractive indices typical of soot. Over the range of the
evaluation, ICP and RDG-FA predictions generally agreed within numeri
cal uncertainties (ca. 10 percent) within the Guinier regime, compleme
nting similar performance of RDG-FA theory in the power-law regime bas
ed on recent experiments. Thus, the use of approximate RBG-FA theory t
o estimate the optical properties of soot appears to be acceptable-par
ticularly in view of the significant uncertainties about soot optical
properties due to current uncertainties about soot refractive indices.