1. What is the Prandtl Number?

The Prandtl number (Pr) or Prandtl group is a dimensionless number, named after the German physicist Ludwig Prandtl, defined as the ratio of momentum diffusivity to thermal diffusivity.

2. How Does the Calculator Work?

The calculator uses the Prandtl Number formula:

Where:

• \( Pr \) — Prandtl Number (dimensionless)
• \( r \) — Recovery Factor (dimensionless)

Explanation: The Prandtl number is calculated as the square of the recovery factor, which is a dimensionless number defined by the ratio of difference in enthalpies.

3. Importance of Prandtl Number Calculation

Details: The Prandtl number is crucial in heat transfer and fluid dynamics calculations as it characterizes the relative thickness of the momentum and thermal boundary layers in fluid flow.

4. Using the Calculator

Tips: Enter the recovery factor value. The value must be valid (greater than 0).

5. Frequently Asked Questions (FAQ)

Q1: What does the Prandtl number represent?
A: The Prandtl number represents the ratio of momentum diffusivity to thermal diffusivity, indicating the relative growth of velocity and thermal boundary layers.

Q2: What are typical Prandtl number values for common fluids?
A: For gases, Pr ≈ 0.7-1.0; for water, Pr ≈ 7; for oils, Pr ≈ 100-1000; for liquid metals, Pr ≈ 0.01-0.1.

Q3: How does Prandtl number affect heat transfer?
A: Lower Pr numbers indicate thermal boundary layers grow faster than velocity boundary layers, while higher Pr numbers indicate the opposite.

Q4: What is the recovery factor in this context?
A: The recovery factor is a dimensionless number defined by the ratio of difference in enthalpies, particularly relevant in high-speed flow and boundary layer analysis.

Q5: Are there limitations to this formula?
A: This specific formula Pr = r² applies to flat plate with viscous flow conditions and may not be applicable to all flow scenarios or geometries.