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Closed Conduit Hydraulics - Friction and Minor Losses

Friction and minor losses are glossed over in the darcy-weisbach article but I want to throw in some extra notes here. Friction occurs over every bit of length of a close-conduit system and is usually a surprisingly high amount of energy loss. Friction depends on the material of the pipe and the velocity of flow. The formula for frictional head loss IS the Darcy-Weisbach equation.

 h_f = f \dfrac{L}{D}\dfrac{V^2}{2g}

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Closed Conduit Hydraulics - Darcy-Weisbach Equation

The Darcy-Weisbach equation is used to determine flow characteristics in closed conduit systems (pipes). It is probably more common than the Hazen-Williams equation due to it being able to solve for systems in both laminar AND turbulent flow.

 h_f = f \dfrac{L}{D} \dfrac{V^2}{2g}

  • headloss h_f (ft)
  • friction factor f, length L
  • length L (ft)
  • diameter D (ft)
  • velocity V \frac{ft}{s}
  • gravity g 32.2 \frac{ft}{s^2}

Friction Factor

The friction factor f is either given or must be calculated using a Moody-Stanton diagram (available in both the AIO and CERM). Getting the friction factor from a Moody-Stanton chart requires the Reynolds Number Re, and relative roughness \dfrac{\epsilon}{D}. Click here to continue reading