Hazen-Williams equation

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The Hazen-Williams formula can be used to calculate the pressure loss in a length of pipe due to friction dependent on the flow. This equation is commonly used for pressure drop calculations in fire sprinkler systems, water distribution systems, and irrigation systems.

P_d=\frac{4.52\quad Q^{1.85}}{C^{1.85}\quad d^{4.87}}

where:

Pd = pressure drop in pounds per square inch / foot

Q = flow in gallons per minute

d = inside pipe diameter (inch)

C = factor (roughness or friction loss coefficient) - the higher the C factor, the smoother the pipe. Typical C factors used in design, which take into account some increase in roughness as pipe ages are as follows:


An alternate form of the Hazen Williams Equation is:

Failed to parse (Cannot write to or create math output directory): V=1.318\quad C\quad R_h^{0.63}\quad S^{0.54}


where:

V = Velocity (in feet per second)

C = as above

Rh = Hydraulic Radius (in feet)

S = Energy Gradient or Friction Slope (hf/L)

Contents

[edit] In SI units

P_d=\frac{102627\quad Q^{1.85}}{C^{1.85}\quad d^{4.87}}

where:

Pd = pressure drop in Pa/m of pipeline

Q = volumetric flow rate in m3/s

d = inside pipe diameter in m

C = as above


Alternatively:

Q = 0,849 \; C \, A \, R_h^{0,63} \, S^{0,54}

Q = Volumetric flow rate

C = factor (friction loss coefficient)

A = Cross-sectional area of flow

Rh = Hydraulic Radius

S = Slope of energy grade line



[edit] See also

[edit] References

  • Turf Irrigation Manual, 5th Ed., by James A. Watkins, published by Telsco, 1987.
  • Fluid Mechanics, 10th Ed., by E. John Finnemore and Joseph B Franzini, published by McGraw Hill, 2002.

[edit] External links

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