on . Posted in Fluid Dynamics Head loss, abbreviated as $$h_l$$, is a pressure loss due to the resistance of the fluid and obstructions along the way in a pipe.  In fluid dynamics, head loss refers to the reduction in total head (pressure energy, kinetic energy, and potential energy) of a fluid as it flows through a pipe or other conduit due to friction between the fluid and the surface of the conduit.  This head loss is also known as friction loss, and it is measured in units of length, such as feet or meters.  The head loss increases with the flow rate of the fluid, the length and diameter of the conduit, and the roughness of the conduit surface.  It is an important consideration in the design and operation of fluid transport systems, as it can affect the efficiency of the system and the required pump or compressor power.

### There are a number of factors that affect head loss

• flow rate
• corrosion and scale deposits
• fittings (bends, elbows, exits, expanders and reducers, tees)
• inside diameter of the pipe
• roughness of the pipe wall
• viscosity of the liquid
• length of the pipe
• straightness of the pipe
• valves

Major head loss, abbreviated as $$h_{l-major}$$, is the pressure drop caused by friction loss.  It does not matter if the pipe is horizontal, vertical or on an incline.

$$\large{ h_{l-major} = f \; \frac{l}{d} \; \frac{v^2}{2\;g} }$$
Symbol English Metric
$$\large{ h_{l-major} }$$ = major head loss  $$\large{ ft }$$  $$\large{ m }$$
$$\large{ f }$$ = friction factor $$\large{ dimensionless }$$
$$\large{ l }$$ = lenght of the pipe $$\large{ ft }$$  $$\large{ m }$$
$$\large{ d }$$ = pipe inside diameter $$\large{ in }$$  $$\large{ mm }$$
$$\large{ v }$$ = velocity of the flow $$\large{ \frac{ft}{sec} }$$ $$\large{ \frac{m}{s} }$$
$$\large{ g }$$ = gravitational constant $$\large{\frac{lbf-ft^2}{lbm^2}}$$  $$\large{\frac{N - m^2}{kg^2}}$$

Minor head loss, abbreviated as $$h_{l-minor}$$, is the pressure drop caused by fittings and valves.

$$\large{ h_{l-minor} = K \; \frac{v^2}{2 \; g} }$$
$$\large{ h_{l-minor} }$$ = minor head loss  $$\large{ft}$$  $$\large{m}$$
$$\large{ K }$$ = loss coefficient $$\large{ dimensionless }$$
$$\large{ v }$$ = velocity of the flow $$\large{ \frac{ft}{sec} }$$   $$\large{ \frac{m}{s} }$$
$$\large{ g }$$ = gravitational constant $$\large{\frac{lbf-ft^2}{lbm^2}}$$  $$\large{\frac{N - m^2}{kg^2}}$$ 