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
$4 \epsilon_{do} \sigma \left(\frac{\theta_{air}}{2} + \frac{\theta_{de}}{2} + 273\right)^{3}$
Related
$\epsilon_{do}$
$\sigma$
$\theta_{air}$