Lewis number

Lewis number 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.

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It is defined as:

where α is the thermal diffusivity and D is the mass diffusivity.

The Lewis number can also be expressed in terms of the Schmidt number and the Prandtl number :

.

See also