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Concept
Résistance hydraulique
Résumé
The term friction loss (or frictional loss) has a number of different meanings, depending on its context.
In fluid flow it is the head loss that occurs in a containment such as a pipe or duct due to the effect of the fluid's viscosity near the surface of the containment.
In mechanical systems such as internal combustion engines, the term refers to the power lost in overcoming the friction between two moving surfaces.
In economics, frictional loss is natural and irrecoverable loss in a transaction or the cost(s) of doing business too small to account for. Contrast with tret in shipping, which made a general allowance for otherwise unaccounted for factors.
Friction loss is a significant engineering concern wherever fluids are made to flow, whether entirely enclosed in a pipe or duct, or with a surface open to the air.
Historically, it is a concern in aqueducts of all kinds, throughout human history. It is also relevant to sewer lines. Systematic study traces back to Henry Darcy, an aqueduct engineer.
Natural flows in river beds are important to human activity; friction loss in a stream bed has an effect on the height of the flow, particularly significant during flooding.
The economies of pipelines for petrochemical delivery are highly affected by friction loss. The Yamal–Europe pipeline carries methane at a volume flow rate of 32.3 × 109 m3 of gas per year, at Reynolds numbers greater than 50 × 106.
In hydropower applications, the energy lost to skin friction in flume and penstock is not available for useful work, say generating electricity.
In refrigeration applications, energy is expended pumping the coolant fluid through pipes or through the condenser. In split systems, the pipes carrying the coolant take the place of the air ducts in HVAC systems.
In the following discussion, we define volumetric flow rate V̇ (i.e. volume of fluid flowing per time) as
where
r = radius of the pipe (for a pipe of circular section, the internal radius of the pipe).
v = mean velocity of fluid flowing through the pipe.
Source officielle
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