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The Hazen–Williams equation is an empirical relationship that relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction. It is used in the design of water pipe systems [ 1 ] such as fire sprinkler systems , [ 2 ] water supply networks , and irrigation systems.
The equation uses an empirically derived constant for the “roughness” of the pipe walls which became known as the Hazen-Williams coefficient. [5] [6] In 1908, Hazen was appointed by President Theodore Roosevelt to a panel of expert engineers to inspect the construction progress on the Panama Canal with President-elect William H. Taft. Hazen ...
c = discharge coefficient (unitless). This is usually 1.0 if using a diffuser. If using a wand to measure the stagnation pressure, the coefficient value depends on the shape of the flow hydrant orifice. A smooth and rounded outlet has c=0.9, a square and sharp outlet has c=0.8, and a square outlet which projects into the barrel has c=0.7.
The most common equation used to calculate major head losses is the Darcy–Weisbach equation. Older, more empirical approaches are the Hazen–Williams equation and the Prony equation. For relatively short pipe systems, with a relatively large number of bends and fittings, minor losses can easily exceed major losses.
Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain-size analyses: = where Hazen's empirical coefficient, which takes a value between 0.0 and 1.5 (depending on literature), with an average value of 1.0. A.F. Salarashayeri & M. Siosemarde indicate C is usually between 1.0 and 1.5, with D in mm and K in cm/s.
By setting the coefficient k to K, the flow rate Q to I and the exponent n to 1, the Hardy Cross method can be used to solve a simple circuit. However, because the relation between the voltage drop and current is linear, the Hardy Cross method is not necessary and the circuit can be solved using non-iterative methods.
n is 1.85 for Hazen-Williams and; n is 2 for Darcy–Weisbach. The clockwise specifier (c) means only the flows that are moving clockwise in our loop, while the counter-clockwise specifier (cc) is only the flows that are moving counter-clockwise. This adjustment doesn't solve the problem, since most networks have several loops.
This page was last edited on 12 March 2009, at 11:41 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may ...