Friction Loss

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Friction loss, abbreviated as FL, is how much loss of flow through a pipe is due to the viscosity, the measure of the internal friction/resistance to the flow of a liquid near the surface of the pipe.   

 

Friction loss formulas

\(\large{ FL = C \; \frac{ Q }{ 100 }^2  \;  \frac{ l }{ 100 }   }\) 
\(\large{ FL = C \; Q_1^2 \; l_1  }\)

Where:

 Units English Metric
\(\large{ FL }\) = friction loss \(\large{ lbf }\) \(\large{ N }\)
\(\large{ l }\) = length of pipe \(\large{ ft }\) \(\large{ m }\)
\(\large{ l_1 }\) = length of pipe / 100 \(\large{ ft }\) \(\large{ m }\)
\(\large{ Q }\) = flow rate \(\large{\frac{ft^3}{sec}}\) \(\large{\frac{m^3}{s}}\)
\(\large{ Q_1 }\) = flow rate / 100 \(\large{\frac{ft^3}{sec}}\) \(\large{\frac{m^3}{s}}\)
\(\large{ C }\) = friction loss coefficient  \(\large{ dimensionless }\)

 

Related formulas

\(\large{ FL = \frac{ h_l }{ l }  }\)  (hydraulic slope) 
\(\large{ FL =  \frac{ 1 }{ \rho \; g } \; \frac{ p_c }{ l }  }\) (hydraulic slope) (related to pressure change)
\(\large{ FL = \frac{ 64 \; \nu }{ 2 \; g } \; \frac{ v }{ d^2 } }\) (laminar flow)

Where:

\(\large{ FL }\) = friction loss

\(\large{ \rho }\)   (Greek symbol rho) = density of fluid

\(\large{ g }\) = standard gravity

\(\large{ h_l }\) = head loss

\(\large{ d }\) = inside diameter of pipe

\(\large{ \nu }\)  (Greek symbol nu) = kinematic viscosity

\(\large{ l }\) = length of pipe

\(\large{ p_c }\) = pressure change

\(\large{ v }\) = velocity of fluid

 

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Tags: Pipe Sizing Equations Friction Equations