Darcy Weisbach Equation

The Darcy Weisbach Equation for calculating the pipe losses is as below;


In the Darcy–Weisbach Equation, the friction factor f  can be calculated from the equation of Colebrook–White.


 where k is the absolute roughness of the pipe wall (mm), D the inner diameter of the pipe (mm) and Re the Reynolds number .

To avoid iterative calculation, Barr (1975) suggests the following acceptable approximation, which deviates from the results obtained by the Colebrook–White Equation for  1%:


 The Reynolds number describes the flow regime. It can be calculated as:


where ν (m2/s) stands for the kinematic viscosity. This parameter depends on the water temperature and can be determined from the following equation:


Where, T is temperature in Degree Centigrade.

Moody’s Diagram