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

MeanFreePath (last edited 2020-05-08 05:43:32 by KeithLofstrom)