Transport coefficient
Transport coefficients indicate how strongly a physical system reacts to a disturbance of the equilibrium. Transport coefficients thus also describe how quickly a system comes into thermodynamic equilibrium .
Transport coefficients appear in transport laws:
With:
- the flux density of any physical quantity
- the transport coefficient of this size
- , the associated driving force, which is specified as a gradient of a scalar quantity.
Transport coefficients can be described by Green-Kubo relations :
where is an observable, an ensemble mean, and the point over which is a time derivative. It applies .
For times that are greater than the correlation time of the fluctuations in the observable, the transport coefficient can also be described by a generalized Einstein relation:
In the general case the transport coefficient can be tensor.
Examples
- Diffusion constant , see Fick's first law for the associated transport law
- Thermal conductivity , see Fourier's law for the associated transport law
-
Shear viscosity with
- ,
- where is the stress tensor , see Newton's fluid for the corresponding transport law
- Electrical conductivity , see Ohm's law for the associated transport law
See also
literature
- Plawsky, Joel L., 1957-: Transport phenomena fundamentals . Third ed. Boca Raton, ISBN 978-1-4665-5535-8 .
Individual evidence
- ↑ a b c d e Plawsky, Joel L., 1957-: Transport phenomena fundamentals . Third ed. Boca Raton, ISBN 978-1-4665-5535-8 .
- ^ A b Water in Biology, Chemistry, and Physics: Experimental Overviews and Computational Methodologies, G. Wilse Robinson, ISBN 9789810224516 , p. 80, Google Books