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Table of Contents:

**Lewis Number :**

Le = α/ D_{c}

**Thermal Diffusivity :**

α = Le* D_{c}

**Mass Diffusivity :**

D_{c} = α/Le

**Where,**

Le = Lewis Number,

α = Thermal Diffusivity,

D_{c} = Mass Diffusivity.

The Lewis Number is a dimensionless number. Lewis Number refers to the study of combined heat and mass transfer. Lewis number is defined as the ratio of thermal diffusivity to mass diffusivity. The Lewis Number is denoted by the symbol 'Le'. Here, diffusion describes the movement of a chemical species A through a binary mixture of A and B due to the presence of a concentration gradient.

The measurement of Lewis Number is equal to the thermal diffusivity that is divided by the diffusion coefficient. The advanced online Lewis Number Calculator is useful in calculating the ratio of thermal and mass diffusivity.

__Example__:

Calculate the Lewis Number for the given details.

Thermal Diffusivity (α) = 25 m^{2}/s

Mass Diffusivity (D_{c}) = 25 m^{2}/s

__Solution__:

**Apply Formula:**

Le = α/ D_{c}

Le = 25/20

Le = 0.8

**Lewis Number (Le) = 0.8**