Practice Question: Head Loss Due to Friction (Hazen-Williams)
NCEES Civil PE Specification V.D.: Pressure conduit
Problem
A new 14-inch diameter welded steel pipe (C = 130), 300 feet in length, is used as a firewater line in an industrial facility. Given a required outlet pressure of 20 psi and a flow of 750 gallons per minute, calculate the necessary inlet pressure.
Assume changes in head loss are only due to friction.
Select an Answer:
CORRECT 😃
INCORRECT 😟
% Students Correctly Answered:
28.0%
Solution
Answer: C) 33.1 psi
Pressure drop in a pipe can be determined by its relation to head loss.
$$ \Delta p=p_{in}-p_{out}=h_f\ast\gamma $$
Where:
$$ h_f=head\ loss\ due\ to\ friction $$
$$ \gamma=specific\ weight\ of\ fluid\ (62.4\frac{lb}{ft^3}\ for\ water) $$
Using the Hazen-Williams equation, we can determine the approximate head loss:
$$ h_f=\frac{10.44\ast L\ast Q^{1.85}}{C^{1.85}\ast d^{4.87}} $$
where:
$$ L=length\ of\ pipe\ \left(feet\right)=300\ ft $$
$$ Q=flow\ \left(gallons\ per\ minute\right)=750\ gpm $$
$$ C=roughness\ coefficient\ \ \left(unitless\right)=130 $$
$$ d=diameter\ of\ pipe\ \left(inches\right)=14\ in $$
