Moody Diagram (Friction Factor)
Follow us on Twitter
Contact us at contact@myengineeringtools.com
| Section Summary |
|---|
| 1. How to find friction factor graphically? |
| 2. Interactive Friction Factor Calculator |
| 3. The Moody Diagram |
| 4. Rules of Thumb & Safety Limits |
1. How to find the friction factor?
The friction factor is used to calculate the pressure drop due to the flow of a fluid in a pipe. It represents the interaction between the fluid and the pipe wall. While historically solved graphically via the Moody Diagram, modern engineering uses correlations like the Churchill Correlation for calculation.
The relationship for relative roughness is defined as:
\[ \text{Relative Roughness} = \frac{\varepsilon}{D} \]The Reynolds number (\(Re\)) determines the flow regime:
\[ Re = \frac{\rho \cdot v \cdot D}{\mu} \]2. Moody Diagram
The Moody diagram helps to answer very quickly: what is the friction factor in pipes? This diagram was generated using the Churchill Correlation, which is valid for all flow regimes.
Note: If you need the Fanning friction factor, divide the Darcy factor from this graph by 4:
\[ f_{Fanning} = \frac{f_{Darcy}}{4} \]Engineering Rules of Thumb
- Laminar Flow: \(Re < 2000\). Friction is independent of roughness.
- Transition Zone: \(2000 < Re < 4000\). Flow is unstable; design margins should be increased.
- Turbulent Flow: \(Re > 4000\). Friction depends heavily on relative roughness.
- Standard Roughness: Commercial Steel is typically \(0.045 \text{ mm}\) (\(0.00015 \text{ ft}\)).
- Liquid Velocity: Usually kept between \(1.0 - 2.5 \text{ m/s}\) to balance pressure drop vs. erosion.
1. Compressor Power
2. Pump Power
3. Pipe Pressure Drop
4. Fluid Velocity
5. Churchill Correlation