1. What is Prandtl Number?

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 formula:

Where:

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

Explanation: This formula calculates the Prandtl number by squaring the recovery factor, which is valid for gases in laminar flow conditions.

3. Importance of Prandtl Number

Details: Prandtl number is crucial in heat transfer calculations as it characterizes the relative thickness of the momentum and thermal boundary layers. It helps determine the rate of heat transfer in fluid flow systems.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range of Prandtl numbers for gases?
A: For most gases, Prandtl numbers typically range from 0.7 to 1.0 at standard conditions.

Q2: Why is the recovery factor squared in this formula?
A: The relationship Pr = r² is derived from boundary layer theory for laminar flow of gases, where the recovery factor is related to the square root of the Prandtl number.

Q3: What is the physical significance of the recovery factor?
A: Recovery factor is a dimensionless number defined by the ratio of difference in enthalpies, particularly important in high-speed flow and heat transfer calculations.

Q4: Are there limitations to this formula?
A: This specific relationship (Pr = r²) is valid primarily for laminar flow of gases. Different relationships may apply for turbulent flow or different fluid types.

Q5: How does Prandtl number affect heat transfer?
A: Lower Prandtl numbers indicate that heat diffuses quickly compared to momentum, while higher Prandtl numbers indicate the opposite.