Chemicals in the Environment, Diffusive Transport

  • Edward CusslerEmail author


Diffusion is mixing without stirring. It is mixing caused by Brownian motion, that is, by thermally induced random motion of molecules or small particles. Because diffusion is often slow, it frequently limits the overall rate of the process. Diffusion has the reputation of being a difficult subject, which it can be; however, the difficulty most often comes from complicated units, from interfaces, or from the combination of diffusion and convection. By itself, diffusion is not hard. It is easier than viscous flow and much easier than ideas like entropy or chemical potential.


Diffusion Coefficient Mass Transfer Coefficient Dispersion Coefficient Concentration Unit Knudsen Diffusion 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



Mass transfer effected by flow due to applied forces like pressure (forced convection) or to density differences (free convection).


Mixing caused by molecular motion.

Diffusion coefficient

The negative of the flux per concentration gradient.


Another name for the diffusion coefficient.


Mixing caused by diffusion and simultaneous flow.


Mass or moles transferred per area per time.

Mass transfer

Diffusion and dispersion, especially across interfaces.

Mass transfer coefficient

The flux per concentration difference, especially near an interface.

Overall mass transfer coefficient

The flux per virtual concentration difference from one phase across an interface into a second phase.


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Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  1. 1.Department of Chemical EngineeringUniversity of MinnesotaMinneapolisUSA

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