# Closed Conduit Hydraulics - Hazen Williams Equation

Hazen-Williams can be used to determine the flow characteristics in closed conduits (pipe systems).

### For Velocity

S = slope, in decimal form. This is equivalent to $h_f/L$

R = hydraulic radius, $\text{(Area of flow)}/\text{(wetted perimeter)}$

C = Roughness Coefficient, get this from a tableÂ (available in both theÂ AIOÂ andÂ CERM)

To derive theseÂ $h_f/L$ has been substituted for S.

The Hazen-Williams equation is similar to the Darcy-Weisbach equation, but it is only used for turbulent flow.

### When to use Hazen-Williams

1. You are only given C
2. You prefer it and are sure the flow is turbulent (Reynolds number (Re) > 4000)
3. You are directly told to (from the examples it looks like several problem prompts do this)

### When to NOT use Hazen-Williams

1. The flow is NOT turbulent (Re < 2100)
2. You are given $f$. If you are given a friction factor use Darcy-Weisbach