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Friction Loss

 

Friction Loss Formula

FL \;=\;  f \cdot   \dfrac{ l }{ d }  \cdot   \dfrac{ v^2 }{ 2 \cdot g }
Symbol English Metric
FL = Friction Loss lbf N
f = Friction Factor dimensionless dimensionless
l = Pipe Length ft m
d = Pipe Inside Diameter in   mm
v = Fluid Velocity  ft\;/\;sec   m\;/\;s
g = Standard Gravity  ft\;/\;sec^2     m\;/\;s^2

Friction loss, abbreviated as FL, also known as frictional pressure loss or head loss, is the loss of pressure that occurs as a result of fluid flow through a conduit or pipe due to the frictional resistance between the fluid and the conduit walls.  It is a significant factor in fluid flow systems and plays a crucial role in determining the required pumping power, flow rates, and system efficiency.  Friction loss is primarily caused by the shear stress between the moving fluid and the conduit's surface.  As the fluid flows through the pipe, it experiences resistance due to the viscous interactions between the fluid layers and the conduit walls.  This resistance leads to energy dissipation in the form of heat, resulting in a decrease in pressure along the flow direction.

Friction Loss Formula

FL \;=\;    C \cdot    \left(  \dfrac{  Q }{ 100 } \right)^2    \cdot   \dfrac{ l }{ 100 }  
Symbol English Metric
FL = Friction Loss lbf N
C = Friction Loss Coefficient dimensionless dimensionless
Q = Flow Rate ft^3\;/\;sec m^3\;/\;s
l = Pipe Length ft m

The calculation of friction loss is typically based on empirical equations, such as the Darcy-Weisbach equation or the Hazen-Williams equation, which take into account factors like pipe diameter, flow velocity, pipe roughness, and fluid properties.  These equations provide estimates of the pressure drop or head loss associated with fluid flow through a particular pipe or conduit.

Understanding friction loss is crucial for system design, hydraulic analysis, and equipment sizing in various applications, including water distribution networks, HVAC systems, industrial piping, and fire protection systems.  Minimizing friction loss through careful pipe selection, optimizing flow velocities, and reducing pipe roughness can improve system efficiency and reduce energy consumption.

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