Lewis Number Calculator

Enter value and click on calculate. Result will be displayed.

Formula:
Lewis Number (Le) = α / Dc

Select calculator :
 
Thermal Diffusivity (α) :
m/s2
Mass Diffusivity (Dc) :
m/s2
Result:

What is the Lewis Number?
The Lewis number (Le) is a dimensionless number used in fluid dynamics and heat transfer, representing the ratio of thermal diffusivity to mass diffusivity. It’s defined as:

Where:

  • α = Thermal diffusivity
  • D = Mass diffusivity
  • k = Thermal conductivity
  • ρ = Density of the fluid
  • cp​ = Specific heat capacity at constant pressure

Why use a Lewis Number Calculator?
A Lewis number calculator helps quickly determine the Lewis number without manually working through the formula. It’s useful when studying heat and mass transfer in processes like combustion, drying, and material cooling, where the interaction of thermal and mass diffusion rates is critical.

How does a Lewis Number Calculator work?
It typically takes the following inputs:

  • k (Thermal conductivity)
  • ρ (Density)
  • cp​ (Specific heat capacity)
  • D (Mass diffusivity)

It calculates:

Then finds the Lewis number:

When do you use it?
You use the Lewis number when analyzing:

  • Heat and mass transfer in combustion
  • Evaporation and condensation processes
  • Cooling and drying of materials
  • Environmental studies (e.g., atmospheric diffusion)