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# 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, D 12 , for binary gas mixtures where air is in large excess.

Air - Diffusion Coefficients of Gases in Excess of Air
Gases in large excess of air Diffusion coefficient, D 12 , [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

## Related Topics

### • Air Psychrometrics

Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.

### • Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

### • Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

### • Material Properties

Properties of gases, fluids and solids. Densities, specific heats, viscosities and more.

## Related Documents

### Air - Composition and Molecular Weight

Dry air is a mechanical mixture of nitrogen, oxygen, argon and several other gases in minor amounts.

### Air - Density vs. Pressure and Temperature

Air density at pressure ranging 1 to 10 000 bara (14.5 - 145000 psi) and constant selected temperatures.

### Air - Density, Specific Weight and Thermal Expansion Coefficient vs. Temperature and Pressure

Online calculator, figures and tables showing density, specific weight and thermal expansion coefficients of air at temperatures ranging -100 to 1600 °C (-140 to 2900 °F) at atmospheric and higher pressure - Imperial and SI Units.

### Air - Dynamic and Kinematic Viscosity

Online calculator, figures and tables with dynamic (absolute) and kinematic viscosity for air at temperatures ranging -100 to 1600°C (-150 to 2900°F) and at pressures ranging 1 to 10 000 bara (14.5 - 145000 psia) - SI and Imperial Units.

### Air - Humidity Ratio

The mass of water vapor present in moist air - to the mass of dry air.

### Air - Moisture Holding Capacity vs. Temperature

The moisture holding capacity of air increases with temperature.

### Air - Molecular Weight and Composition

Dry air is a mixture of gases where the average molecular weight (or molar mass) can be calculated by adding the weight of each component.

### Air - Prandtl Number

Prandtl number for air vs. temperature and pressure.

### Air - Properties at Gas-Liquid Equilibrium Conditions

Properties of air change along the boiling and condensation curves (temperature and pressure between triple point and critical point conditions). An air phase diagram included.

### Air - Specific Heat vs. Pressure at Constant Temperature

Figures and tables with isobaric (Cp) and isochoric (Cv) specific heat of air at constant temperature and pressure ranging 0.01 to 10000 bara.

### Air - Specific Heat vs. Temperature at Constant Pressure

Online calculator with figures and tables showing specific heat (Cp and Cv) of dry air vs. temperature and pressure. SI and imperial units.

### Air - Speed of Sound vs. Temperature

Speed of sound in air at standard atmospheric pressure with temperatures ranging -40 to 1000 °C (-40 to 1500 °F) - Imperial and SI Units.

### Air - Thermal Conductivity vs. Temperature and Pressure

Online calculator with figures and tables showing air thermal conductivity vs. temperature and pressure. SI and imperial units.

### Air - Thermal Diffusivity vs. Temperature and Pressure

Figures and tables withdry air thermal diffusivity vs. temperarure and pressure. SI and Imperial units.

### Air - Thermophysical Properties

Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.

### Air Conditioning - Cooling of Air and Condensate Generated

Water may condensate when air is cooled in air conditioning systems.

### Carbon Dioxide Concentration in Rooms Occupied with People

Carbon dioxide concentration in a room may indicate air quality and ventilation system efficiency.

### Compressed Air - Pressure Drop Diagrams, Metric Units

Pressure loss in compressed air pipe lines.

### Dry Air - Thermodynamic and Physical Properties

Thermodynamic properties of dry air - specific heat, ratio of specific heats, dynamic viscosity, thermal conductivity, Prandtl number, density and kinematic viscosity at temperatures ranging 175 - 1900 K.

### Gases Solved in Water - Diffusion Coefficients

Diffusion flux [kg/m2s] tells how fast a substanse solved in another substance flows due to concentration gradients. Diffusion constants [m2/s] for several gases in water.

### Moist Air - Specific Volume

Specific volume of moist air is defined as the total volume of humid air per mass unit of dry air

### Moist Air - Weight of Water Vapor

Weight of water vapor in air

### Solubility of Air in Water

The amount of air that can be dissolved in water decreases with temperature and increases with pressure.

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