1. What is Reynolds Number?

The Reynolds number is a dimensionless quantity used to predict flow patterns in different fluid flow situations. It compares inertial forces to viscous forces and helps determine whether flow will be laminar or turbulent.

2. How Does the Calculator Work?

The calculator uses the Reynolds number equation with mass flow rate:

Where:

• \( Re \) — Reynolds number (dimensionless)
• \( \dot{m} \) — Mass flow rate (kg/s)
• \( D \) — Diameter of pipe or characteristic length (m)
• \( \mu \) — Dynamic viscosity of the fluid (Pa·s)

Explanation: This form of the equation is particularly useful when you know the mass flow rate rather than the velocity of the fluid.

3. Importance of Reynolds Number

Details: The Reynolds number is crucial in fluid mechanics for determining flow regimes:

• Re < 2000: Laminar flow
• 2000 < Re < 4000: Transitional flow
• Re > 4000: Turbulent flow

4. Using the Calculator

Tips: Enter mass flow rate in kg/s, diameter in meters, and dynamic viscosity in Pa·s. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between this and the velocity-based Reynolds number?
A: Both calculate the same dimensionless number, but this version uses mass flow rate instead of velocity, making it more convenient for certain applications.

Q2: What are typical viscosity values?
A: Water at 20°C has μ ≈ 0.001 Pa·s, while honey has μ ≈ 10 Pa·s. Air at 20°C has μ ≈ 1.8×10⁻⁵ Pa·s.

Q3: Does this work for non-circular pipes?
A: For non-circular conduits, use the hydraulic diameter as the characteristic length D.

Q4: What if I know volumetric flow rate instead of mass flow?
A: Convert using ṁ = ρQ, where ρ is density and Q is volumetric flow rate.

Q5: How does temperature affect the calculation?
A: Temperature affects viscosity significantly. Always use viscosity values appropriate for your fluid's temperature.