Heat transfer coefficient for radiation

Heat transfer coefficient for radiation in channel acc. Heinhold eq. 18.21

Symbol
$\alpha_{st}$
Unit
W/K/m$^2$
Formulae
$\frac{K_{t} \sigma \left(\left(\theta_{de} + 273\right)^{4} - \left(\theta_{t} + 273\right)^{4}\right)}{\Delta \theta_{s}}$
Related
$\Delta \theta_{s}$
$\sigma$
$\theta_{de}$
$\theta_{t}$