Radiation heat transfer coefficient, duct to air

Radiation heat transfer coefficient from outer surface of the duct used for riser/J-tube to ambient air.

Symbol
$h_{rad,da}$
Unit
W/(K.m$^2$)
Formulae
$4\sigma \epsilon_{do} \left(\frac{\theta_{de}+\theta_{air}}{2}+\theta_{abs}\right)^3$
Related
$\sigma$
$\theta_{abs}$
$\theta_{air}$