1. What is the Nusselt Number?

The Nusselt number (Nu) is a dimensionless number that represents the ratio of convective to conductive heat transfer across a boundary. It's widely used in heat transfer calculations to characterize the efficiency of convection relative to conduction.

2. How Does the Calculator Work?

The calculator uses the Nusselt number equation:

Where:

• \( h \) — Heat transfer coefficient (W/m²K)
• \( l \) — Characteristic length (m)
• \( k \) — Thermal conductivity of the fluid (W/mK)

Explanation: The Nusselt number compares the actual heat transfer to the heat transfer that would occur through pure conduction.

3. Importance of Nusselt Number

Details: The Nusselt number is crucial for designing heat exchangers, cooling systems, and any application involving convective heat transfer. It helps engineers predict heat transfer rates and optimize thermal systems.

4. Using the Calculator

Tips: Enter the heat transfer coefficient in W/m²K, characteristic length in meters, and thermal conductivity in W/mK. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is characteristic length?
A: Characteristic length depends on geometry - for a flat plate it's the length along flow direction, for a pipe it's the diameter.

Q2: What are typical Nusselt number values?
A: For laminar flow, Nu is typically 3-5. For turbulent flow, it can range from 10 to several hundred.

Q3: How does Nu relate to Reynolds and Prandtl numbers?
A: For forced convection, Nu is often correlated with Re and Pr (e.g., Dittus-Boelter equation).

Q4: What's the difference between local and average Nu?
A: Local Nu varies along the surface, while average Nu gives the overall heat transfer performance.

Q5: When is this simple Nu equation not applicable?
A: For complex geometries or combined heat transfer modes, empirical correlations or CFD may be needed.