# Nusselt number, gas to duct

Symbol
$\mathrm{Nu}_{gd}$
Formulae
 $0.1103 \mathrm{Gr}_{gd} \mathrm{Pr}_{gas}$ Riser open at both ends, $Gr \cdot Pr < 10$ (Anders) $0.62 \left(\mathrm{Gr}_{gd} \mathrm{Pr}_{gas}\right)^{0.25}$ Riser open at both ends, otherwise (Anders) $\frac{\mathrm{Gr}_{gd} \mathrm{Pr}_{gas}}{400}$ Riser open at top and closed at bottom, $Gr \cdot Pr < 200$ (Anders) $0.35 \left(\mathrm{Gr}_{gd} \mathrm{Pr}_{gas}\right)^{0.28}$ Riser open at top and closed at bottom, otherwise (Anders) $0.63 \left(\mathrm{Gr}_{gd} \mathrm{Pr}_{gas}\right)^{0.25}$ Riser open at both ends, 0.1 ≤ $Ra$ < 10^5 (Hartlein & Black IIb) $0.1445 \left(\mathrm{Gr}_{gd} \mathrm{Pr}_{gas}\right)^{0.28}$ Riser open at top and closed at bottom, $10^{4.95} ≤ Gr \cdot Pr ≤ 10^{6.15}$ (Hartlein & Black)
Related
$\mathrm{Gr}_{gd}$
$\mathrm{Pr}_{gas}$
Used in
$h_{conv_{gd}}$