Major Loss Calculation for Water in Pipes using Hazen-Williams Friction Loss Equation

Hazen-Williams friction loss equation is valid for water at temperatures typical of city water supply systems (40 to 75 oF; 4 to 25 oC).

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Hazen-Williams Equations

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k is a unit conversion factor:
k=1.318 for English units (feet and seconds).  k=0.85 for SI units (meters and seconds)
Rh=hydraulic radius=D/4 for circular pipe

The Hazen-Williams method is only valid for water flowing at ordinary temperatures (about 40 to 75 oF).  For other liquids or gases, the Darcy-Weisbach method should be used.  Major loss (hf) is the energy (or head) loss (expressed in length units - think of it as energy per unit weight of fluid) due to friction between the moving fluid and the duct.  It is also known as friction loss.  The Darcy-Weisbach method is generally considered more accurate than the Hazen-Williams method.   However, the Hazen-Williams method is very popular, especially among civil engineers, since its friction coefficient (C) is not a function of velocity or duct diameter.  Hazen-Williams is simpler than Darcy-Weisbach for calculations where you are solving for flowrate, velocity, or diameter.  More  Discussion and References.


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