Grashof number, gas to duct

Symbol
$\mathrm{Gr}_{gd}$
Formulae
$\frac{g \beta_{gas} {\delta_d}^4}{L_d {\nu_{gas}}^2} \left(\theta_e-\theta_{air}\right)$Riser open at both ends
$\frac{g \beta_{gas} \left(\frac{D_{di}}{2}\right)^4}{L_d {\nu_{gas}}^2} \left(\theta_{gas}-\theta_{di}\right)$Riser open at top and closed at bottom
Used in
$\mathrm{Nu}_{gd}$
$\mathrm{Ra}_{gas}$