Numerical investigation of the effect of soot aggregation on the radiative properties in the infrared region and radiative heat transfer

被引:25
作者
Eymet, V
Brasil, AM
El Hafi, M
Farias, TL
Coelho, PJ
机构
[1] Univ Tecn Lisboa, Inst Super Tecn, Dept Engn Mech, P-1049001 Lisbon, Portugal
[2] Ecole Mines Albi, Ctr Energet Environn, F-81000 Albi, France
[3] Univ Fed Pernambuco, Dept Mech Engn, BR-50740530 Recife, PE, Brazil
关键词
soot; scattering; fractal aggregates; Rayleigh-Debye-Gans/fractal aggregate (RDG-FA) theory; integral equation formulation for scattering (IEFS);
D O I
10.1016/S0022-4073(01)00280-1
中图分类号
O43 [光学];
学科分类号
070207 ; 0803 ;
摘要
The effect of aggregation on soot radiative properties in the infrared region of the spectrum is numerically investigated using Rayleigh-Debye-Gans theory for fractal aggregates (RDG-FA). In order to use the RDG-FA theory for a wide range of aggregate sizes and wavelengths, the predicted phase functions, scattering and absorption coefficients are compared with a more accurate theory, the integral equation formulation for scattering-IEFS. The importance of scattering when compared with absorption is investigated, as well as the effect of aggregation on the phase function shape and on the scattering cross section. It is concluded that in the case of small aggregates formed with small primary particles the scattering coefficient is negligible compared with the absorption coefficient, and scattering and aggregation of primary particles can be ignored. Thus, the Rayleigh approximation can be used leading to isotropic scattering. In the case of large aggregates constituted by large primary: particles, aggregation becomes important and the scattering cross section is of the same order of magnitude.,of the absorption cross section. Moreover, the phase function becomes highly peaked in the forward direction. Therefore, the Rayleigh and the equivalent volume Mie sphere approximations are not valid, and the RDG-FA method emerges as a good compromise between accuracy and simplicity of application. However, radiative transfer calculations between. two infinite, parallel, black walls show that scattering may always be neglected in the calculation of total radiative heat source and heat fluxes to the walls. The minor influence of scattering on the accuracy of the predictions is explained by the shift between the spectral region where scattering is important and the region where the spectral radiative heat source is large. (C) 2002 Elsevier Science Ltd. All rights reserved.
引用
收藏
页码:697 / 718
页数:22
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