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:8/23/2017)... 2017  The general public,s help is being enlisted in what,s thought ... in and on the human body –and are believed to affect health.  ... The Microbiome Immunity Project is the ... with the gut. The project's goal is to help advance scientific knowledge ... ...
(Date:6/23/2017)... and ITHACA, N.Y. , ... and Cornell University, a leader in dairy research, today ... bioinformatics designed to help reduce the chances that the ... the onset of this dairy project, Cornell University has ... for Sequencing the Food Supply Chain, a food safety ...
(Date:5/16/2017)... May 16, 2017   Bridge Patient Portal ... and MD EMR Systems , an electronic ... for GE, have established a partnership to build ... and the GE Centricity™ products, including Centricity Practice ... These new integrations will allow healthcare ...
Breaking Biology News(10 mins):
Other biology definition