Transport coefficient

A transport coefficient measures how rapidly a perturbed system returns to equilibrium.

The transport coefficients occur in transport phenomenon with transport laws

where:

is a flux of the property
the transport coefficient of this property
, the gradient force which acts on the property .

Transport coefficients can be expressed via a Green–Kubo relation:

where is an observable occurring in a perturbed Hamiltonian, is an ensemble average and the dot above the A denotes the time derivative.[1] For times that are greater than the correlation time of the fluctuations of the observable the transport coefficient obeys a generalized Einstein relation:

In general a transport coefficient is a tensor.

Examples

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Transport coefficients of higher order

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For strong gradients the transport equation typically has to be modified with higher order terms (and higher order Transport coefficients).[2]

See also

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References

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  1. ^ Water in Biology, Chemistry, and Physics: Experimental Overviews and Computational Methodologies, G. Wilse Robinson, ISBN 9789810224516, p. 80, Google Books
  2. ^ Kockmann, N. (2007). Transport Phenomena in Micro Process Engineering. Deutschland: Springer Berlin Heidelberg, page 66, Google books