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.
- headloss (ft)
- friction factor , length
- length (ft)
- diameter (ft)
- gravity g
The friction factor 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 , and relative roughness .
The absolute roughness is usually given by what material the pipe is made of (e.g. cast iron, concrete, streel) and requires a table look up. The relative roughness is this table value divided by the diamater .
Where V is the velocity of the fluid, D is the diameter, and v is the kinamatic viscosity of the fluid. The standard kinematic viscosity to use is .
Find the line that corresponds to the relative roughness and follow it to where it lines up with the Reynold Number. The friction factor is directly horizontal from that point. Practice looking these things up the Moody-Stanton graph will become your fast friend!
Remember and to keep units in check.