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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Design of Circular Water Pipes Calculator
Table of Hazen-Williams Coefficients (C) Unit Conversions
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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