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| '''Friction loss''' is the loss of energy or “head” that occurs in pipe flow due to viscous effects generated by the surface of the pipe.<ref>{{cite book|last=Munson|first=B.R.|title=Fundamentals of Fluid Mechanics 5th Edition|year=2006|publisher=Wiley & Sons|location=Hoboken, NJ}}</ref> Friction Loss is considered as a "major loss" and it is not to be confused with “minor loss” which includes energy lost due to obstructions. In mechanical systems such as [[internal combustion engine]]s, it refers to the power lost overcoming the friction between two moving surfaces.
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| This energy drop is dependent on the wall shear stress (τ) between the fluid and pipe surface. The shear stress of a flow is also dependent on whether the flow is turbulent or laminar. For turbulent flow, the pressure drop is dependent on the roughness of the surface, while in laminar flow, the roughness effects of the wall are negligible. This is due to the fact that in turbulent flow, a thin viscous layer is formed near the pipe surface which causes a loss in energy, while in laminar flow, this viscous layer is non-existent.<ref>{{cite book|last=Munson|first=B.R.|title=Fundamentals of Fluid Mechanics 5th Edition|year=2006|publisher=Wiley & Sons|location=Hoboken, NJ}}</ref>
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| == Causes ==
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| Friction loss has several causes, including:
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| * Frictional losses depend on the conditions of flow and the physical properties of the system.
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| * Movement of fluid [[molecules]] against each other
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| * 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
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| * Bends, kinks, and other sharp turns in [[Hose (tubing)|hose]] or [[piping]]
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| 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.
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| == Calculating friction loss ==
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| One of the accepted methods to calculate friction losses resulting from fluid motion in pipes is by using the Darcy-Weisbach Equation. For a circular pipe:<ref>{{cite journal|last=Brown|first=G.O.|title=The History of the Darcy-Weisbach Equation for Pipe Flow Resistance|year=2003}}</ref>
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| : <math>h_l = f_D \left ( \frac{L}{D} \right ) \left ( \frac{V^2}{2g} \right )</math>
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| where:
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| : h<sub>l</sub> = Head Loss due to friction, given in units of length | |
| : f<sub>D</sub> = Darcy friction factor (see [[Darcy–Weisbach equation#Confusion with the Fanning friction factor|Confusion with the Fanning friction factor ]])
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| : L = Pipe Length
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| : D = Pipe Diameter
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| : V = Flow velocity
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| : g = [[Gravitational Constant]]
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| ==References==
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| {{reflist}}
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| ==External links==
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| * [http://www.enggcyclopedia.com/welcome-to-enggcyclopedia/fluid-dynamics/line-sizing-calculator Pipe pressure drop calculator] for single phase flows.
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| * [http://www.enggcyclopedia.com/welcome-to-enggcyclopedia/fluid-dynamics/pipe-pressure-drop-calculator-phase Pipe pressure drop calculator for two phase flows.]
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| * [http://pfcalc.sourceforge.net Open source pipe pressure drop calculator.]
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| [[Category:Fluid dynamics]]
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| [[Category:Fluid mechanics]]
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| [[Category:Mechanical engineering]]
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| [[Category:Piping]]
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