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In fluid dynamics, the Darcy–Weisbach equation is a phenomenological equation, which relates the head loss, or pressure loss, due to friction along a given length of pipe to the average velocity of the fluid flow for an incompressible fluid. The equation is named after Henry Darcy and Julius Weisbach. The Darcy–Weisbach equation contains a dimensionless friction factor, known as the Darcy friction factor. This is also called the Darcy–Weisbach friction factor, resistance coefficient, or simply friction factor. The Darcy friction factor is four times the Fanning friction factor, with which it should not be confused.〔 See page 293.〕 == Head loss form == Head loss ''h''''f'' due to viscous effects in a circular cross section of pipe with length ''L'' can be characterized by the Darcy Weisbach equation:〔 :; where; * ''hf'' is the head loss due to friction (SI units: m); Note: This is also proportional to the piezometric head along the pipe; * ''L'' is the length of the pipe (m); * ''D'' is the hydraulic diameter of the pipe (for a pipe of circular section, this equals the internal diameter of the pipe) (m); * ''V'' is the average flow velocity, experimentally measured as the volumetric flow rate per unit cross-sectional wetted area (m/s); * ''g'' is the local acceleration due to gravity (m/s2); * ''f''''D'' is a dimensionless parameter called the Darcy friction factor, resistance coefficient, or simply friction factor.〔See paragraph 3〕 The Darcy friction factor ''f''''D'' can be found from a Moody diagram or it can be calculated (see below). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Darcy–Weisbach equation」の詳細全文を読む スポンサード リンク
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