# Kinematic viscosity for gas

The kinematic viscosity (also called momentum diffusivity) is the ratio of the dynamic viscosity $\mu$ to the density $\rho$.

It is a convenient concept when analyzing the Reynolds number, which expresses the ratio of the inertial forces to the viscous forces.

Symbol
$\nu_{gas}$
Unit
m$^2$/s
Formulae
 $-1.1555{\cdot}{10}^{-14} {T_{gas}}^3+9.5728{\cdot}{10}^{-11} {T_{gas}}^2+0.7604{\cdot}{10}^{-8} T_{gas}+3.4484{\cdot}{10}^{-6}$ air @ 1 bar (Dumas&Trancossi2009) $\frac{\eta_{gas}}{\rho_{gas}}$ general formula for gases
Related
$\eta_{gas}$
$\rho_{gas}$
Gas density [kg/m$^3$]
$T_{gas}$