The equations behind pfcalc - The Pipe Friction Calculator


This section describes the equations employed by pfcalc (pipe friction calculator) to compute pressure drop in piping systems. For a description of the program and it's GUI front-ends and for download locations see the pfcalc home page.

The program operates on an arbitrary number of pipes. For each pipe, the following equations are solved:

  1. Velocity:
    v = 4 * Q / pi / d / d [m/s]
  2. Reynolds number:
    Rey = d * v / ν [-]
  3. Friction factor:
    λ = 64 / Rey, for Rey less than or equal to 2300; 1/sqrt(λ) = -2log(k/3.71*d + 2.51/(Rey*sqrt(λ))), for Rey greater than or equal to 4000; For Rey between 2300 and 4000, λ is found by linear interpolation
  4. Major pressure loss (Darcy-Weisbach):
    Δp major = λ * ρ * v * v / 100000 / 2 [bar]
  5. Minor pressure loss:
    Δp minor = K * &ρ * v * v / 100000 / 2 [bar]
  6. Hydrostatic pressure loss:
    Δp hydrostatic = ρ * g * z / 100000 [bar]
  7. Total pressure drop:
    Δp total = Δp major + Δp minor + Δp hydrostatic [bar]

Note that the Colebrook-White equation (formula 3 for Reynolds numbers larger than 4000) is an implicit equation and is solved by an iterative method.

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The contact details can be found on the pfcalc home page.

Last update

This page was last updated on 23/11/2012.

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