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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
$h_{rad,ext}$
Unit
W/(K.m$^2$)
Formulae
$\sigma \epsilon_{do} \left(\theta_{de}+\theta_{abs}+\theta_{air}+\theta_{abs}\right) \left(\left(\theta_{de}+\theta_{abs}\right)^2+\left(\theta_{air}+\theta_{abs}\right)^2\right)$
Related
$\epsilon_{do}$
Emissivity of duct outer surface
$\sigma$
Stefan Boltzmann constant [W/m$^2$K$^4$]
$\theta_{abs}$
Absolute temperature [K]
$\theta_{air}$
Ambient air temperature [°C]
$\theta_{de}$
Temperature of duct outer wall [°C]
Used in
$T_{4iii}$
Thermal resistance to ambient [K.m/W]