Mean Free Path
From CRC100:
l |
mean free path |
m |
d |
hard sphere diameter |
m |
P |
pressure |
Pa| |
\eta |
viscosity |
μPa s |
m |
molecular mass |
kg |
M |
molar mass |
g/mole |
\tau |
mean time between collisions |
s |
\overline v |
mean velocity |
m/s |
l = { \Large { { k T } \over { \pi \sqrt{ 2 } P d^2 } } } ~ = ~ { \Large { 9.27e-27 \over { d^2 } } }
d^2 = 2.669E-20 \sqrt( M T ) / \eta ~~~ m² ... compute diameter from viscosity
\overline{ v } = { \Large \left( { 8 k T } \over { \pi m } \right) } = 145.5\sqrt(T/M) ~~~ m/s
At 25C and 100KPa (or STP?):
gas |
d |
l |
\overline v |
\tau |
\eta |
|
Å |
nm |
m/s |
ps |
μPa s |
NH₃ |
4.32 |
49.7 |
609 |
82 |
10.2 |
Ar |
3.58 |
72.2 |
397 |
182 |
22.7 |
CO₂ |
4.53 |
45.1 |
379 |
119 |
14.9 |
He |
2.15 |
200 |
1256 |
159 |
19.9 |
H₂ |
2.71 |
126 |
1769 |
71 |
8.9 |
Kr |
4.08 |
55.8 |
274 |
203 |
25.4 |
Ne |
2.54 |
143 |
559 |
256 |
32.0 |
N₂ |
3.70 |
67.6 |
475 |
142 |
17.8 |
O₂ |
3.55 |
73.6 |
444 |
166 |
20.7 |
Xe |
4.78 |
4.05 |
219 |
185 |
23.1 |
H₂O |
|
|
|
|
9.9 |
CO |
|
|
|
|
17.8 |
CH₄ |
|
|
|
|
11.1 |
also CRC Handbook of Thermophysics p407