1. Introduction

2. Colebrook equation

The friction factor is used to
calculate the pressure drop due to the flow of a fluid in a pipe. It
represents the interaction in between the fluid and the pipe. **There
are different ways to calculate it, one can be graphical, using a
Moody graph, but for automating calculation it is not practical,
thus correlations are required. The Colebrook correlation is usually
admitted as being accurate enough for most industrial application.**

Note : log base 10

With :f = Darcy friction factor

Dh = Hydraulic diameter (m)

Re = Reynolds number

ε = pipe roughness (m)

Note that Colebrook equation is not explicit, thus it requires some iterations to solve it. To have a direct expression, with an acceptable accuracy, you can use Churchill equation.