# Prandtl number for gas

The Prandtl number is a dimensionless number, defined as the ratio of kinematic viscosity (also called momentum diffusivity) to thermal diffusivity.

Equation for humid air is taken from paper by P.T. Tsilingiris: 'Thermophysical and transport properties of humid air at temperature range between 0 and 100°C', 2007

Symbol
$\mathrm{Pr}_{gas}$
Formulae
 $0.7215798365-3.703124976{\cdot}{10}^{-4} \theta_{gas}+2.240599044{\cdot}{10}^{-5} {\theta_{gas}}^2-4.162785412{\cdot}{10}^{-7} {\theta_{gas}}^3+4.969218948{\cdot}{10}^{-9} {\theta_{gas}}^4$ humid air @ 1 atm (Tsilingiris2007) $\frac{c_{p,gas} \eta_{gas}}{k_{gas}}$ general formula for gases
Related
$c_{p,gas}$
$\eta_{gas}$
$k_{gas}$
$\theta_{gas}$