In the previous chapters refrence was made to some essential properties of hydrogen, helium, frequently used as a safe model fluid, and air into which both gases are dispersed.
| property | H2 | He | air |
|---|
| density (at NTP 1 atm, 20°C) | 0.0835 kg/m^3 | 0.166 kg/m^3 | 1.21 kg/m^3 |
| kinematic viscosity | 1.05 10^{-4} m^2/s | 1.15 10^{-4} m^2/s | 1.51 10^{-4} m^2/s |
| diffusion coefficient | 6.1 10^{-5} m^2/s | 5.7 10^{-5} m^2/s | ... m^2/s |
| diffusion coefficient in air | 7.5 10^{-5} m^2/s | ... 10^{-5} m^2/s | ... m^2/s |
| sonic speed (at 1 atm, 20°C) | 1306 m/s | 1005 m/s | 300 m/s |
