Navigation Links
Fick's law of diffusion


Fick's laws of diffusion describe diffusion.

Contents

History

Fick's laws of diffusion were derived by Adolf Fick in the year 1858.

Fick's First Law

Fick's First Law is used in steady state diffusion, i.e., when the concentration within the diffusion volume does not change with respect to time (Jin=Jout).

Where

  • J is the diffusion flux in dimensions of [parts length-2 time-1]
  • D is the diffusion coefficient in dimensions of [length2 time-1]
  • c is the concentration in dimensions of [parts length-3]
  • x is the position

Fick's Second Law

Fick's Second Law is used in non-steady state diffusion, i.e., when the concentration within the diffusion volume changes with respect to time.

Where

  • c is the concentration in dimensions of [parts length-3]
  • t is time
  • D is the diffusion coefficient in dimensions of [length2 time-1]
  • x is the position

A Biological Perspective

The first law gives rise to the formula

It states that the rate of diffusion of a gas across a membrane is

  • Constant for a given gas at a given temperature by an experimentally determined factor, K
  • Proportional to the surface area over which diffusion is taking place, A
  • Proportional to the difference in partial pressures of the gas across the membrane, P2 - P1
  • Inversely proportional to the distance over which diffusion must take place, or in other words the thickness of the membrane, D.

Fick's first 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

References

  • W.F. Smith, Foundations of Materials Science and Engieering 3rd ed., McGraw-Hill (2004)

'"/>


(Date:4/5/2017)... 2017  The Allen Institute for Cell Science today ... one-of-a-kind portal and dynamic digital window into the human ... first application of deep learning to create predictive models ... and a growing suite of powerful tools. The Allen ... future publicly available resources created and shared by the ...
(Date:4/4/2017)... --  EyeLock LLC , a leader of iris-based identity ... and Trademark Office (USPTO) has issued U.S. Patent No. ... iris image with a face image acquired in sequence ... th issued patent. "The issuance ... multi-modal biometric capabilities that have recently come to market ...
(Date:3/30/2017)... , March 30, 2017 The research team ... for three-dimensional (3D) fingerprint identification by adopting ground breaking 3D fingerprint ... new realm of speed and accuracy for use in identification, crime ... affordable cost. ... A ...
Breaking Biology News(10 mins):
Other biology definition