Ficks law of diffusion
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Fick's Law of Diffusion states that the rate of diffusion of a gas across a fluid membrane is

• proportional to the difference in partial pressure
• proportional to the area of the membrane
• inversely proportional to the thickness of the membrane

Fick's law is also important in radiation transfer equations. However, in this context it becomes inaccurate when the diffusion constant is low and the radiation becomes limited by the speed of light rather than by the resistance of the material the radiation is flowing through. In this situation, one can use a flux limiter.

The exchange rate of a gas across a fluid membrane can be determined by using this law together with Graham's law.

See also : lung -- alveoli

The original article can be found at: http://en.wikipedia.org/wiki/Ficks_law_of_diffusion.
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