Colebrook correlation (friction factor)

Piping Systems
Equivalent length key pipe components
Singularity coefficient key pipe components
Partially filled pipe
Sonic Velocity
Valves types
Valves Cv
Control valve sizing for gases
Pressure safety valves
Colebrook correlation
Churchill correlation
Velocity in pipes
Flow regimes
Orifice calculations

1. Introduction

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 that the friction factor used here is Darcy (also called Darcy-Wesibach or Moody) friction factor.

2. Colebrook equation

Colebrook equation

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.