Engineering
Swamee-Jain Explicit Pipe Friction Factor formula (Moody Chart)
Estimate a Darcy pipe-friction factor with explicit Swamee–Jain arithmetic in a declared turbulent range, use 64/Re for laminar flow, and leave the transition region unresolved.
Keep the friction-factor convention and flow regime explicit
This example models steady, fully developed flow of a Newtonian fluid in a full circular pipe. B2 is absolute roughness and B3 is internal diameter in the same length units; B4 is the positive dimensionless Reynolds number. Darcy and Fanning factors differ by a factor of four.
The worksheet uses 64/Re below Re=2000, and deliberately leaves 2000<=Re<5000 unresolved rather than assigning a turbulent value. For the turbulent approximation it selects 5000<=Re<=100000000 and 0.000001<=roughness/diameter<=0.01. Zero roughness is allowed as an ideal smooth-pipe calculation, without a claimed accuracy guarantee.
Swamee–Jain is an explicit approximation, not an exact solution to Colebrook. The selected bounds are a worksheet policy, not a universal guarantee of a specified error. EPANET uses separate laminar, transition and turbulent treatments; this example does not implement its transition interpolation.
D2 keeps the unrounded Darcy value. D3 derives the Fanning value from that same branch, including laminar cases. Round only when displaying or testing values; do not feed a rounded factor into downstream pressure-drop calculations.
Darcy friction factor in D2
Invalid inputs and cases outside the selected range return an explanatory message. No factor is produced for Re=3200.
=IF(COUNT(B2:B4)<>3,"Enter numeric pipe inputs",IF(OR(B2<0,B3<=0,B4<=0),"Require roughness>=0, diameter>0 and Re>0",IF(B4<2000,64/B4,IF(B4<5000,"Transition or outside selected turbulent range",IF(OR(B4>100000000,B2/B3>0.01,AND(B2>0,B2/B3<0.000001)),"Outside selected approximation range",0.25/(LOG10(B2/(3.7*B3)+5.74/B4^0.9)^2))))))Fanning friction factor in D3
The convention conversion applies to whichever valid Darcy branch D2 returned. It is not a second independent turbulent-only calculation.
=IF(ISNUMBER(D2),D2/4,D2)Try the example
Use the original values or change them to test your understanding.