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'''Lewis number''' ('''Le''') is a [[dimensionless number]] defined as the ratio of [[thermal diffusivity]] to [[mass diffusivity]]. It is used to characterize [[fluid]] flows where there is simultaneous heat and mass transfer by convection.

It is defined as:
:<math>\mathrm{Le} = \frac{\alpha}{D}</math>

where <math>\alpha</math> is the thermal diffusivity and <math>D</math> is the mass diffusivity.

The Lewis number can also be expressed in terms of the [[Schmidt number]] and the [[Prandtl number]] :
:<math>\mathrm{Le} = \frac{\mathrm{Sc}}{\mathrm{Pr}}</math>.

It is named after [[Warren K. Lewis]] (1882–1975),<ref>W. K. Lewis: ''The Evaporation of a Liquid Into a Gas'' In: ''Transactions of the American Society of Mechanical Engineers'', No. 1849, 1922, p. 325-340.</ref><ref>A. Klinkenberg, H. H. Mooy: ''Dimensionless Groups in Fluid Friction, Heat, and Material Transfer'' In: ''Chemical Engineering Progress'', Vol. 44, No. 1, 1948, p. 17-36.</ref> who was the first head of the Chemical Engineering Department at [[MIT]]. Some workers in the field of combustion assume (incorrectly) that the Lewis number was named for Bernard Lewis (1899–1993), who for many years was a major figure in the field of combustion research.

==Literature==
*{{cite journal
| last = Bird
| first = R.B.
| authorlink =
| year = 2001
| title = Who Was Who in Transport Phenomena
| doi =
| url = http://cee.che.ufl.edu/Journals/fall2001/F2001contents.html
| accessdate = 2008-02-08
}}
*{{cite book
| last = Incropera
| first = F. P.
| authorlink = Frank P. Incropera
|coauthors = DeWitt, D. P.
| year = 1996
| title = Heat and Mass Transfer, fifth edition
| isbn = 0-471-38650-2
| doi =
| publisher = Wiley
| location = New York, NY
}}

==References==
<references />

==See also==
{{NonDimFluMech}}

{{DEFAULTSORT:Lewis Number}}
[[Category:Dimensionless numbers]]
[[Category:Fluid dynamics]]

{{fluiddynamics-stub}}

Locality preserving hashing - Revision history

en>Phil Boswell: {{cite doi}}