Air - Diffusion Coefficients of Gases in Excess of Air
Fick's first law states that a substance will flow from a region with high concentration to a region of low concentration . Fick's law can be expressed as
J = -D*dφ/dx [1]
where
J = diffusion flux - the amount of substance that flows through an unit area per unit time [mass or mol /(m2s)]
D = diffusion coefficient [m2/s]
dφ = change in concentration of substance [mass or mol/m3 ]
dx = change in length [m]
For simple one-dimensional transport, the diffusion coefficient describes the time–rate of change of concentration . The diffusion coefficient varies from substance to substance and with temperature and pressure.
Figure and table below shows the diffusion coefficients, D12 , for binary gas mixtures where air is in large excess.
See also Air Composition and molecular weight , Density at varying pressure, Density and specific weight at varying temperature , Diffusion coefficients for gases in air , Dynamic (absolute) and kinematic viscosity , Prandtl Number , Specific heat at varying temperature and Specific heat at varying pressure , Thermal conductivity , Thermal diffusivity , Properties at gas-liquid equilibrium conditions and Air properties , for other properties of air, as well as Diffusion coefficients of gases in water and Carbon dioxide concentrations in rooms with people
| Gases in large excess of air | Diffusion coefficient, D12 , [cm2/s] at atmospheric pressure and given temperatures | ||||||
|---|---|---|---|---|---|---|---|
| 0 °C | 20 °C | 100 °C | 200 °C | 300 °C | 400 °C | ||
| Name | Formula | 32 °F | 68 °F | 212 °F | 392 °F | 572 °F | 752 °F |
| Argon | Ar | 0.167 | 0.189 | 0.289 | 0.437 | 0.612 | 0.81 |
| Methane | CH4 | 0.21 | 0.321 | 0.485 | 0.678 | 0.899 | |
| Carbon monoxide | CO | 0.208 | 0.315 | 0.475 | 0.662 | 0.875 | |
| Carbon dioxide | CO2 | 0.16 | 0.252 | 0.39 | 0.549 | 0.728 | |
| Hydrogen | H2 | 0.668 | 0.756 | 1.153 | 1.747 | 2.444 | 3.238 |
| Water vapour | H2O | 0.219 | 0.242 | 0.399 | 0.638 | 0.873 | 1.135 |
| Helium | He | 0.617 | 0.697 | 1.057 | 1.594 | 2.221 | 2.933 |
| Sulfur hexafluoride | SF6 | 0.15 | 0.233 | 0.329 | 0.438 | ||
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