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Rayleigh number riser—air

Rayleigh number $c_{Nu}$ gas/duct

Symbol
$\mathrm{Ra}_{ext}$
Formulas
$\mathrm{Gr}_{ext} \mathrm{Pr}_{gas}$duct to ambient
$\frac{g \mathrm{Pr}_{gas} \beta_{gas} \left(\theta_{de}-\theta_{air}\right) {L_d}^3}{{\nu_{gas}}^2}$Chippendale, IEC
Related
$\beta_{gas}$
Volumetric thermal expansion coefficient gas [1/K]
$g$
Standard acceleration of gravity [m/s$^2$]
$\mathrm{Gr}_{ext}$
Grashof number riser—air
$L_d$
Length duct [m]
$\nu_{gas}$
Kinematic viscosity gas [m$^2$/s]
$\mathrm{Pr}_{gas}$
Prandtl number gas
$\theta_{air}$
Ambient air temperature [°C]
$\theta_{de}$
Temperature duct outer surface [°C]
Used in
$h_{conv,ext}$
Heat transfer coefficient convection riser—air [W/(K.m$^2$)]