Radiation heat transfer, object to duct

Radiation heat transfer from envelope around cables to inner wall of the duct used for riser/J-tube.

Symbol
$W_{rad,od}$
Unit
W/m
Formulae
$\sigma \pi D_o K_r \left(\left(\theta_e+\theta_{abs}\right)^4-\left(\theta_{di}+\theta_{abs}\right)^4\right)$