Enter the thermal diffusivity (m^2/s) and the mass diffusivity (m^2/s) into the Calculator. The calculator will evaluate the Lewis Number.
Lewis Number Formula
Le = a / Dc
Variables:
- Le is the Lewis Number ()
- a is the thermal diffusivity (m^2/s)
- Dc is the mass diffusivity (m^2/s)
To calculate Lewis Number, divide the thermal diffusivity by the mass diffusivity.
How to Calculate Lewis Number?
The following steps outline how to calculate the Lewis Number.
- First, determine the thermal diffusivity (m^2/s).
- Next, determine the mass diffusivity (m^2/s).
- Next, gather the formula from above = Le = a / Dc.
- Finally, calculate the Lewis Number.
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
thermal diffusivity (m^2/s) = 15
mass diffusivity (m^2/s) = 123
Frequently Asked Questions (FAQ)
What is thermal diffusivity?
Thermal diffusivity is a measure of how quickly heat can spread through a material. It is defined as the thermal conductivity divided by the product of the material’s density and specific heat capacity, with units of m^2/s.
How does mass diffusivity differ from thermal diffusivity?
While thermal diffusivity relates to the spread of heat within a material, mass diffusivity (also known as the diffusion coefficient) refers to the rate at which particles or solutes spread out in a medium, due to concentration gradients, also measured in m^2/s.
Why is the Lewis Number important?
The Lewis Number is a dimensionless number that characterizes the ratio of thermal to mass diffusivity. It is important in the study of convective heat and mass transfer processes, indicating whether heat or mass transfer dominates in a given situation.
Can the Lewis Number be greater than 1?
Yes, the Lewis Number can be greater than 1, less than 1, or equal to 1, depending on the relative values of thermal and mass diffusivity. A Lewis Number greater than 1 indicates that thermal diffusivity dominates, while a number less than 1 suggests mass diffusivity is more significant.
