Lewis Number Calculator

Introduction

The Lewis Number Calculator is a valuable tool in the field of fluid mechanics and heat transfer. It helps engineers and researchers understand the relative importance of mass transfer to heat transfer in a fluid flow process. Named after the British scientist Warren K. Lewis, this dimensionless number plays a crucial role in designing and optimizing various industrial processes involving heat and mass transfer.

Formula

The Lewis Number (Le) is defined as:

Le=κα​

Where:

• $Le$ is the Lewis Number.
• $\alpha$ is the thermal diffusivity of the fluid.
• $\kappa$ is the mass diffusivity of the fluid.

How to Use

Using the Lewis Number Calculator is straightforward:

1. Obtain the values for thermal diffusivity ($\alpha$) and mass diffusivity ($\kappa$) of the fluid in question. These properties are typically available in engineering reference books or databases.
2. Enter the values of $\alpha$ and $\kappa$ into the calculator.
3. Click the “Calculate” button to find the Lewis Number ($Le$).

Example

Let’s consider an example involving air at a certain temperature and pressure:

• Thermal diffusivity of air ($\alpha$): 0.25 cm²/s
• Mass diffusivity of air ($\kappa$): 0.20 cm²/s

Using the formula, we can calculate the Lewis Number ($Le$):

=0.25 cm²/s0.20 cm²/s=1.25Le=0.20cm²/s0.25cm²/s​=1.25

In this case, the Lewis Number for air is 1.25.

FAQs

What does a Lewis Number greater than 1 indicate?

A Lewis Number greater than 1 suggests that thermal diffusion is more significant than mass diffusion in the fluid flow process. This means that heat transfer dominates over mass transfer.

What does a Lewis Number less than 1 indicate?

Conversely, a Lewis Number less than 1 indicates that mass diffusion is more significant than thermal diffusion. In such cases, mass transfer plays a more critical role than heat transfer.

Conclusion

The Lewis Number Calculator is a valuable tool for engineers and researchers involved in heat and mass transfer processes. By understanding the relative importance of mass and heat transfer, they can design more efficient and effective systems for various applications, including chemical engineering, environmental engineering, and materials processing. Whether you’re analyzing natural convection, combustion processes, or any other fluid flow phenomenon, the Lewis Number provides essential insights into the underlying physics.