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
G
k
for the spectral band
k
is solution of the following equation,
(4-133)
,
where
•
D
P1,
k
is the P1 diffusion coefficient, defined as
•
a
1,
k
is the linear Legendre coefficient of the scattering phase function
•
Q
r,
k
is the radiative heat source:
(4-134)
.
,
,
.