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Thermal Molecular Velocity of Gas Molecules Formulas and Calculator

Fluid Dynamics Engineering and Design

Thermal Molecular Velocity of Gas Molecules Formulas and Calculator

Gas molecules in a vessel move back and forth in different directions and at different speeds. Their velocity distribution corresponds to a bell curve having its peak at the most probable velocity

Probable Velocity

cw = [ ( 2 · R · T ) / M ]1/2

Mean Thermal Velocity

cmean = [ ( 8 · R · T ) / ( π · M ) ]1/2

Where:

cw = Probable Velocity (m/s),
cmean = Mean Velocity (m/s),
R = General gas constant R = 8.314510 kJ / (kmol K),
T = Thermodynamic temperature [K],
M = Molar mass [kg / kmol]

Molar masses and mean thermal velocities of various gases

Gas
Molar Mass (g/mol)
Mean Velocity (m/s)
Mach Number
H2
2
1,762
5.3
He
4
1,246
3.7
H2O
18
587
1.8
N2
28
471
1.4
Air
29
463
1.4
Ar
40
394
1.2
CO2
44
376
1.1

Thermal Molecular Velocity of Gas Molecules

Related:

References:

  • Karl Jousten (Hrsg.), Wutz Handbuch Vakuumtechnik,
  • Pupp / Hartmann, Vakuumtechnik Carl Hanser Verlag
  • Schweitzer, Bleuler, Traxler, Active Magnetic Bearings, Hochschulverlag AG an der ETH Zürich
  • Fremerey, Vacuum 32 (1982) S.
  • Hobson und Redhead, Can. J. Phys. 36 (1958)
  • Redhead, Electron Stimulated Desorption, Vacuum 12 (1962)
  • Dawson, Quadrupol Mass Spectrometry, Elsevier Amsterdam (1976)
  • Brubaker, 14th National Symposium, Am. Vac. Soc. (1967)
  • Fachbericht Balzers BG 800003 Das Funktionsprinzip des Quadrupol Massenspektrometers. (1990)
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