Lewis Number Calculator

The Lewis Number (Le) represents the ratio of thermal diffusivity to mass diffusivity. This dimensionless number is pivotal in the study of combined heat and mass transfer processes, especially in fluid mechanics and chemical engineering.

Historical Background

The concept of the Lewis Number was introduced by Warren K. Lewis, an American chemical engineer, in the early 20th century. It has since become a fundamental parameter in the analysis of convective heat and mass transfer phenomena.

Calculation Formula

The Lewis Number is calculated using the formula:

\[ Le = \frac{\alpha}{D_c} \]

Where:

• \(Le\) is the Lewis Number,
• \(\alpha\) is the thermal diffusivity (m²/s),
• \(D_c\) is the mass diffusivity (m²/s).

Example Calculation

For thermal diffusivity \(\alpha = 12\) m²/s and mass diffusivity \(D_c = 16\) m²/s, the Lewis Number (Le) is calculated as:

\[ Le = \frac{12}{16} = 0.75 \]

Importance and Usage Scenarios

The Lewis Number is crucial for engineers and scientists to design and analyze systems involving heat and mass transfer. It is widely used in the optimization of chemical reactors, the study of atmospheric phenomena, and the design of heat exchangers.

Common FAQs

1. What does a high Lewis Number indicate?

   • A high Le indicates that heat diffuses much faster than mass.

2. How does the Lewis Number affect heat and mass transfer?

   • The Lewis Number helps in understanding the relative rates of heat and mass transfer. A Le close to 1 means that heat and mass transfer rates are similar.

3. Can the Lewis Number be less than 1?

   • Yes, if mass diffusivity is greater than thermal diffusivity, Le will be less than 1, indicating faster mass diffusion compared to heat.

Understanding the Lewis Number and its implications allows for more efficient and effective design and operation of systems involving heat and mass transfer.