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In fluid dynamics the Borda–Carnot equation is an empirical description of the mechanical energy losses of the fluid due to a (sudden) flow expansion. It describes how the total head reduces due to the losses. This in contrast with Bernoulli's principle for dissipationless flow (without irreversible losses), where the total head is a constant along a streamline. The equation is named after Jean-Charles de Borda (1733–1799) and Lazare Carnot (1753–1823). This equation is used both for open channel flow as well as in pipe flows. In parts of the flow where the irreversible energy losses are negligible, Bernoulli's principle can be used. == Formulation == The Borda–Carnot equation is:〔Chanson (2004), p. 231.〕〔Massey & Ward-Smith (1998), pp. 274–280.〕 : where *''ΔE'' is the fluid's mechanical energy loss, *''ξ'' is an empirical loss coefficient, which is dimensionless and has a value between zero and one, 0 ≤ ''ξ'' ≤ 1, *''ρ'' is the fluid density, *''v''1 and ''v''2 are the mean flow velocities before and after the expansion. In case of an abrupt and wide expansion the loss coefficient is equal to one.〔 In other instances, the loss coefficient has to be determined by other means, most often from empirical formulae (based on data obtained by experiments). The Borda–Carnot loss equation is only valid for decreasing velocity, ''v''1 > ''v''2, otherwise the loss ''ΔE'' is zero – without mechanical work by additional external forces there cannot be a gain in mechanical energy of the fluid. The loss coefficient ''ξ'' can be influenced by streamlining. For example in case of a pipe expansion, the use of a gradual expanding diffuser can reduce the mechanical energy losses.〔. See pp. 347–349.〕 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「Borda–Carnot equation」の詳細全文を読む スポンサード リンク
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