Hazen-Williams equation is a popular approach for the calculation of head loss of liquid in piping systems. In this method, Hazen-Williams coefficient is introduced to the equation, the coefficient eliminates the need for using Reynolds number. The Hazen-Williams coefficient is mainly used to account for the pipe roughness or efficiency.
Hazen-Williams equation
Different formats for this equation is specified below
Equation 1 (US Units)
Hazen-Williams equation for head loss is shown below:
Where;
H = frictional head loss, ft
L = length of pipe, ft
D = inside diameter of pipe, ft
Q = flow rate, ft3/s
C = Hazen-Williams C factor or roughness coefficient, dimensionless
Equation 2 (US Units)
Where;
H = friction loss, ft of water per 1000 ft of pipe
Q = flow rate, gal/min
D = inside diameter of pipe, in
C = Hazen-Williams C coefficient, dimensionless
Equation 3 (US Units)
Where;
Pmi = friction loss, psi per mile of pipe
Q = flow rate, gal/min
D = inside diameter of pipe, in
C = Hazen-Williams C coefficient, dimensionless
Equation 4 (US Units) – Flow rate
Where;
H = friction loss, ft of water per 1000 ft of pipe
Q = flow rate, gal/min
D = inside diameter of pipe, in
C = Hazen-Williams C coefficient, dimensionless
Equation 5 (SI Units)
Where;
Q = flow rate, m3/h
D = pipe inside diameter, mm
Pkm = frictional pressure drop, kPa/km
SG = liquid specific gravity (water = 1.00)
C = Hazen-Williams C factor, dimensionless
Common values for the Hazen-Williams coefficient C are listed in the table below:
| Pipe material | C Factor |
| Brick | 100 |
| Cast iron (old) | 100 |
| Iron (worn/pitted) | 60 – 80 |
| Polyvinyl chloride (PVC) | 150 |
| Smooth wood | 120 |
| Smooth masonry | 120 |
| Smooth pipes (all metals) | 130 – 140 |
| Vitrified clay | 110 |
Read about another popular equation for head loss calculations using Darcy-Weisbach equation
