The Hazen Williams coefficient was taken to be 150 per the table in the previous section. The table below was prepared using the equation: Q = 0.442 C D2.63 (ΔP/L)0.54, with units as given above, to calculate the water flow rates for PVC pipe with diameters from 1/2 inch to 6 inches and length from 5 ft to 100 ft, all for a pressure difference of 20 psi across the particular length of pipe. C values typically used for some common pipe materials are shown in the table at the left.Įxample Calculation of Water Flow Rates for Pipe Sizes and Lengths Values of C are available in many handbooks, textbooks, and on internet sites. In order to use the Hazen Williams formula for water flow rate calculations, values of the Hazen Williams coefficient, C, are needed for the pipe material being used. Values for the Hazen Williams Coefficient
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The second page of this article has a table with values for the Hazen Williams coefficient, a table with example water flow rate calculations for several PVC pipe lengths and diameters, and a link to download a spreadsheet template with Excel formulas to make the water flow rate calculations. units, as illustrated in the section after next on the second page. This is a form of the Hazen Williams formula that is convenient to use for estimating water flow rates for pipe sizes and lengths in U.S. ΔP is the pressure difference across pipe length, L, in psi ΔP is the pressure difference across pipe length, L, in kN/m2 units, a convenient form of the equation is: Q = (3.763 x 10-6) C D2.63 (ΔP/L)0.54, where The Hazen Williams formula can also be expressed in terms of the pressure difference (ΔP) instead of head loss (hL) across the pipe length, L, using ΔP = ρghL: Water Flow Rates for Pipe Sizes over a Range of Diameters with the Hazen Williams Formulaįor flow of water under pressure in a circular pipe, the Hazen Williams formula shown above can be rewritten into the following convenient form: Using this relationship and Q = V(πD2/4), for flow in a circular pipe, the Hazen Williams formula can be rewritten as shown in the next section. The Hazen Williams Formula is used primarily for pressure flow in pipes, for which the hydraulic radius is one fourth of the pipe diameter (R = D/4). S = slope of energy grade line = head loss/pipe length = hL/L, which is dimensionless R = Hydraulic radius, ft (R = cross-sectional area/wetted perimeter) units: V = 1.318 C R0.633 S0.54, where:Ĭ = Hazen Williams coefficient, dependent on the pipe material and pipe age The traditional form of the Hazen Williams formula is:
It can be written in terms of water velocity or water flow rate, in terms of pressure drop or head loss, and for several different sets of units. There are several different forms of the Hazen Williams Formula in use for water flow rate calculations. Click on the following link for more details about the Darcy Weisbach Equation.įollowing presentation and discussion of several forms of the Hazen Williams equation in the next couple of sections, a downloadable Excel spreadsheet template will be presented and discussed for making Hazen Williams water flow rate calculations, using Excel formulas. For fluids with viscosity different from water, or for water temperatures far above or below 60oF, the Darcy Weisbach Equation works better than the Hazen Williams Formula.
For a review of this topic see the article, ‘ Reynolds Number and Laminar & Turbulent Flow.’ Strictly speaking, the Hazen Williams formula applies to water at 60oF, but it works quite well for a reasonable range of water temperatures above or below 60oF. Most practical applications of water transport in pipes are in the turbulent flow regime. The turbulent flow requirement is not very limiting. The Hazen Williams formula is an empirical equation that can be used for turbulent flow of water at typical ambient temperatures. Limitations on the Hazen Williams Formula for Water Flow Rate Calculations units can be used in the Excel spreadsheet templates. The Hazen Williams formula is used for water flow rate calculations. Excel formulas to calculate water flow rates for pipe sizes (diameters and lengths) can be downloaded as Excel templates in this article.
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