Friction loss
Encyclopedia
Friction loss refers to that portion of pressure lost by fluids while moving through a pipe, hose, or other limited space. In mechanical systems such as internal combustion engine
s, it refers to the power lost overcoming the friction between two moving surfaces.
In pipe flows the losses due to friction are of two kinds: skin-friction and form-friction. The former is due to the roughness of the inner part of the pipe where the fluid comes in contact with the pipe material, while the latter is due to obstructions present in the line of flow--perhaps a bend, control valve, or anything that changes the course of motion of the flowing fluid.
s, pressures created can sometimes overwhelm the ability of water to flow through a hose of a given diameter. As the velocity of water inside a hose increases, so does the friction loss. This resulting increase occurs as an exponential rate, thus an increase in the flow by a factor of X will result in an increase in friction loss by a factor of X2. For example, doubling the flow through a hose will quadruple the friction loss. Ultimately, as the pressure created by a fire pump goes higher and higher the amount of water actually flowing through a hose to a given point lessens, threatening firefighting operations. Conversely, friction loss can restrict the distance which water can be lifted during fire department drafting operations.
FL = CQ2L
Where
FL = friction loss (expressed in psi
)
C = coefficient of friction
(based on the inside diameter of the hose and the inside jacket material)
Q = flow rate in hundreds of gallons (gpm
/100)
L = Length of hose in hundreds of feet (L/100)
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s, it refers to the power lost overcoming the friction between two moving surfaces.
Causes
Friction loss has several causes, including:- Frictional losses depend on the conditions of flow and the physical properties of the system.
- Movement of fluid molecules against each other
- Movement of fluid molecules against the inside surface of a pipe or the like, particularly if the inside surface is rough, textured, or otherwise not smooth
- Bends, kinks, and other sharp turns in hoseHose (tubing)A hose is a hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called pipes , or more generally tubing...
or pipingPipingWithin industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid....
In pipe flows the losses due to friction are of two kinds: skin-friction and form-friction. The former is due to the roughness of the inner part of the pipe where the fluid comes in contact with the pipe material, while the latter is due to obstructions present in the line of flow--perhaps a bend, control valve, or anything that changes the course of motion of the flowing fluid.
Firefighting Applications
While friction loss has multiple applications, one of the most common is in the realm of firefighting. With the advent of modern power-takeoff (PTO) fire pumpFire pump
A fire pump is a part of a fire sprinkler system's water supply and can be powered by electric, diesel or steam. The pump intake is either connected to the public underground water supply piping, or a static water source . The pump provides water flow at a higher pressure to the sprinkler system...
s, pressures created can sometimes overwhelm the ability of water to flow through a hose of a given diameter. As the velocity of water inside a hose increases, so does the friction loss. This resulting increase occurs as an exponential rate, thus an increase in the flow by a factor of X will result in an increase in friction loss by a factor of X2. For example, doubling the flow through a hose will quadruple the friction loss. Ultimately, as the pressure created by a fire pump goes higher and higher the amount of water actually flowing through a hose to a given point lessens, threatening firefighting operations. Conversely, friction loss can restrict the distance which water can be lifted during fire department drafting operations.
Formulas
The formula used most often in firefighting to express the amount of friction loss is:FL = CQ2L
Where
FL = friction loss (expressed in psi
Pounds per square inch
The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...
)
C = coefficient of friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
(based on the inside diameter of the hose and the inside jacket material)
Q = flow rate in hundreds of gallons (gpm
GPM
GPM may refer to:*GPM , a mouse server for the console and xterm*Gallons per minute, a unit of volumetric flow rate*Gallons per mile, a unit of fuel efficiency*General Purpose Macrogenerator, an early macro processor...
/100)
L = Length of hose in hundreds of feet (L/100)