Schmidt number
Physical key figure | |||||
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Surname | Schmidt number | ||||
Formula symbol | |||||
dimension | dimensionless | ||||
definition | |||||
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Named after | Ernst Schmidt | ||||
scope of application | diffusion |
The Schmidt number (after Ernst Schmidt ) is a dimensionless number in physics. It describes the ratio of diffusive momentum transport to diffusive substance transport as the quotient of the kinematic viscosity of a fluid and the diffusion coefficient of a chemical substance contained in it:
With
The Schmidt number is a clear measure of the ratio of the boundary layer thickness between the hydrodynamic boundary layer and the concentration boundary layer.
At high values ( ) the impulse transport is more pronounced than the mass transport. This applies e.g. B. for liquids ( ), but not for gases ( ).
The Schmidt number is the quotient of the Péclet number , which compares advective with diffusive mass transport, and the Reynolds number , which compares advective with diffusive momentum transport:
With
- the speed
- the characteristic length
- the characteristic diameter
In addition, the Schmidt number is the analogue of the Prandtl number used in heat transfer and is linked to this via the Lewis number :
with the thermal diffusivity .
Individual evidence
- ^ Josef Kunes: Dimensionless Physical Quantities in Science and Engineering . Elsevier, 2012, ISBN 0-12-391458-2 , pp. 263 ( limited preview in Google Book search).
- ↑ tec-science: Schmidt number. In: tec-science. May 9, 2020, accessed on June 25, 2020 (German).