# Closed Conduit Hydraulics – Hazen Williams Equation

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

### For Velocity

$$ V = 1.318CR^{0.63}S^{0.54} \text{ (US)}$$

$$ V = 0.849CR^{0.63}S^{0.54} \text{ (SI)}$$

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 table (available in both the AIO and CERM)

### For Head Loss

To derive these \( h_f/L\) has been substituted for S.

$$ h_f = \frac{0.6V^{1.85}L}{C^{1.85}R^{1.165}} \text{ (US, ft and ft/s)}$$

$$ h_f = \frac{1.35V^{1.85}L}{C^{1.85}R^{1.165}} \text{ (SI, m and m/s)}$$

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

### When to use Hazen-Williams

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

### When to NOT use Hazen-Williams

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

Posted in Water and Environmental Breadth and tagged flow, hazen williams, hydraulics, morning breadth, pe exam, water. Bookmark the permalink. Leave a Comment.

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