DarcyWeisbachvergelijking

The Darcy–Weisbach equation is a fundamental relation in fluid mechanics that expresses the frictional head loss or pressure loss of incompressible, steady flow in a pipe due to friction. It is widely used in civil and mechanical engineering to analyze pipe systems.

The standard form of the equation is hf = f (L/D) (V^2 / 2g), where hf is the friction head loss, f is the Darcy friction factor, L is the pipe length, D is the hydraulic diameter, V is the average flow velocity, and g is the acceleration due to gravity. The friction factor f is dimensionless and depends on the flow regime and pipe roughness.

For laminar flow, which occurs when Re = ρVD/μ is below about 2100, the Darcy friction factor simplifies to f = 64/Re. In turbulent flow, f depends on both Reynolds number and relative roughness ε/D and cannot be expressed by a simple closed form. It is commonly obtained from the Moody chart or estimated by the Colebrook–White implicit equation: 1/√f = -2 log10( (ε/D)/3.7 + 2.51/(Re√f) ). Various explicit approximations exist, such as Swamee–Jain or Haaland, for practical calculations.

The equation is used to compute pressure drops along pipelines, design pumping requirements, and evaluate energy losses in water supply networks, wastewater systems, and HVAC piping. While highly versatile, accurate results require careful selection of the roughness coefficient and appropriate flow regime assessment.