What is the friction factor and how is it determined?

The Darcy friction factor (f) relates frictional pressure drop to flow velocity in pipes via the Darcy-Weisbach equation: dP = f*(L/D)*(rho*v^2/2). For laminar flow: f = 64/Re. For turbulent flow, f depends on Re and relative roughness (e/D), determined from the Moody chart or Colebrook equation. Typical values: smooth pipes 0.01-0.02, rough pipes up to 0.05. The friction factor is essential for calculating pressure drops and sizing pumps for piping systems.