Some properties of tracer gases
Gas
Name
Hydrogen
Helium
Air
molar mass
g/mol
2.016
4.003
28.89
Viskosity
μPa s
8.9
19.8
18.36
thermal
speed
speed
m/s
1770
1256
467
mean free
path
path
μm
198
126
68.5
thermal
conductivity
conductivity
W/m K
0.149
0.183
0.0275