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.
$1.32{\cdot}{10}^{-5}+9.5{\cdot}{10}^{-8} \theta_{gas}$ | humid air @ 1 atm (IEC 60287-2-3) |
$-1.1555{\cdot}{10}^{-14} {T_{gas}}^3+9.5728{\cdot}{10}^{-11} {T_{gas}}^2+0.7604{\cdot}{10}^{-8} T_{gas}+3.4484{\cdot}{10}^{-6}$ | air @ 1 bar (Dumas&Trancossi2009) |
$\frac{\eta_{gas}}{\rho_{gas}}$ | general formula for gases |