# Friction Loss

on . Posted in Classical Mechanics

Friction loss, abbreviated as FL, also known as frictional pressure loss or head loss, refers to 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.

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.

## Friction loss formula

$$\large{ FL = f \; \frac{ l }{ d } \; \frac{ v^2 }{ 2 \; g } }$$
Symbol English Metric
$$\large{ FL }$$ = friction loss  $$\large{ lbf }$$ $$\large{ N }$$
$$\large{ f }$$ = friction factor $$\large{ dimensionless }$$
$$\large{ l }$$ = length of pipe $$\large{ ft }$$  $$\large{ m }$$
$$\large{ d }$$ = inside diameter of pipe $$\large{ in }$$  $$\large{ mm }$$
$$\large{ v }$$ = velocity of fluid  $$\large{\frac{ft}{sec}}$$   $$\large{\frac{m}{s}}$$
$$\large{ g }$$ = standard gravity  $$\large{\frac{ft}{sec^2}}$$     $$\large{\frac{m}{s^2}}$$

## Friction loss formula

$$\large{ FL = C \; \left( \frac{ Q }{ 100 } \right)^2 \; \frac{ l }{ 100 } }$$
Symbol English Metric
$$\large{ FL }$$ = friction loss  $$\large{ lbf }$$ $$\large{ N }$$
$$\large{ C }$$ = friction loss coefficient  $$\large{ dimensionless }$$
$$\large{ Q }$$ = flow rate $$\large{\frac{ft^3}{sec}}$$ $$\large{\frac{m^3}{s}}$$
$$\large{ l }$$ = length of pipe $$\large{ ft }$$  $$\large{ m }$$ 