Orifice (source code)
= Orifice
An <orifice> is a localized opening through which a <fluid> passes, often from a vessel into a region of lower <pressure>. A simple inviscid incompressible estimate for an opening of area $A$ is
$$
Q_{\rm ideal}=A\sqrt{2\Delta p/\rho},
$$
when the reservoir <velocity> and elevation change are negligible and $\Delta p$ is the driving <pressure difference>. The relation follows from a <Bernoulli equation> estimate of exit speed.
Real jets contract and dissipate <energy>, so a <discharge coefficient> $C_d$ is often introduced through $Q=C_dQ_{\rm ideal}$. The <vena contracta> can have a smaller area than the opening itself. Measuring collected fluid per unit <time> and the driving head tests the coefficient for a specified geometry and regime. For substantial <gas> compression or <choked flow>, the incompressible formula must be replaced by an appropriate compressible-flow model.
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