Polychromatic Radiation
As in the Surface-to-Surface Radiation Interface, polychromatic radiation is modeled using the stepwise-gray model (Ref. 23) to account for wavelength dependence of emission, absorption, and scattering through material properties; see the section Wavelength Dependence of Surface Properties.
In the Discrete Ordinates Method (DOM), the Radiative Transfer Equation is solved for each spectral band:
,
where FEP is the fractional emissive power, also presented in the section Wavelength Dependence of Surface Properties.
If the P1 Approximation Theory is used instead, the incident radiation Gk for the spectral band k is solution of the following equation,
(4-133),
where
DP1,k is the P1 diffusion coefficient, defined as
a1,k is the linear Legendre coefficient of the scattering phase function
Qr,k is the radiative heat source:
(4-134).