Nusselt number, surface to air

Symbol
$\mathrm{Nu}_{prot}$
Formulae
$\left(0.6+\frac{0.387{\mathrm{Ra}_{prot}}^{\frac{1}{6}}}{\left(1+\left(\frac{0.559}{\mathrm{Pr}_{gas}}\right)^{\frac{9}{16}}\right)^{0.2963}}\right)^2$
Related
$\mathrm{Pr}_{gas}$