Pipe flow pressure drop

 Flow rate
 Pipe diameter d 10-3 m
 Pipe length L m
 Pipe roughness (RMS) 10-6 m
 Fluid density 103 kg/m3
 Dynamic viscosity 10-3 PaĚs
 Cross section 10-4 m2
 Mean velocity m/s
 Re-number   -
 Relative Roughness e/d   -
 Friction factor f   -
 Pressure drop z m
 Pressure drop

The pressure drop in circular pipes is calculated using Darcy-Weisbach equation:

The flow is considered laminar when Re<2300. In a laminar flow the friction factor f is calculated by f=64/Re.

For Re>2300 the flow is considered turbulent and the friction factor is calculated using the Colebrook interpolation function:

This curve fit equation perfectly describes the curves in the Moody Diagram.

In literature two definitions of the friction factor are found. The SI based and Imperial based friction factor which is exactly four times larger (this calculator).

Moody diagram, Imperial based friction factor

Moody Diagram, SI based friction factor