Major Pressure Loss

Overview

Major pressure loss (also called friction loss or major loss) is the pressure drop due to friction along the length of a straight pipe. It is calculated using the Darcy-Weisbach equation.

Formula

$\Delta P = f \cdot \frac{L}{D} \cdot \frac{\rho v^2}{2}$

Calculator

Notes

• Results are approximate and should be verified for critical applications
• Input values should be within reasonable engineering ranges

Typical Pipe Roughness Values

When using the Darcy-Weisbach equation, the pipe's internal surface roughness (ε) is required to determine the friction factor (f). The roughness depends heavily on the pipe material and its condition.

Flow Regime and Friction Factor

The friction factor (f) is not a constant; it depends on the Reynolds Number (Re) and the relative roughness (ε/D). The flow regime is critical:

• Laminar Flow (Re < 2300): The friction factor depends only on the Reynolds number and is given by $f = \frac{64}{Re}$.
• Turbulent Flow (Re > 4000): The friction factor depends on both Reynolds number and relative roughness. It is determined iteratively using the Colebrook-White equation:

$$\frac{1}{\sqrt{f}} = -2 \log_{10} \left( \frac{\epsilon/D}{3.7} + \frac{2.51}{Re \sqrt{f}} \right)$$

For full turbulence (high Re), the friction factor depends only on roughness and is described by the Von Kármán equation:

$$\frac{1}{\sqrt{f}} = -2 \log_{10} \left( \frac{\epsilon/D}{3.7} \right)$$

The Moody Chart is a graphical representation of these relationships and is a standard tool for estimating the friction factor.

Interactive Charts

References

• Original Source