Magnitude of the Fanning friction factor

Considering laminar flow first, the Fanning friction factor introduced in equation (4.20) depends only on the Reynolds number, Npe  

Equation (4.24) allows the Fanning friction factor to be found during laminar flow for both incompressible fluids and compressible fluids, i.e. liquids and gases. 

Whether flow is laminar or turbulent depends on the size of the Reynolds number. Flow is laminar when the Reynolds number is below 2000, and it will be essentially turbulent when the Reynolds number is in excess of about 4000, but between Reynolds numbers of about 

Once more, this expression applies equally to liquids and gases. 

Since commercial pipe is normally relatively smooth, with an s/D of between 0.002 and 0.0002, it follows approximately Blasius s equation for perfectly smooth pipe, with c = 0, up to a Reynolds number of 100000  

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