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A ratio between actual volumetric flowrate through the the real orifice and volumetric flowrate  estimate through the ideal orifice:

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LaTeX Math Inline
body\Delta p

pressure drop on the choke

LaTeX Math Inline
body\Delta p = p_{in} - p_{out}

LaTeX Math Inline
body\beta = \frac{d}{D}

chokeorifice narrowing ratio

LaTeX Math Inline
bodyd

orifice diameter

LaTeX Math Inline
bodyD

pipe diameter 

LaTeX Math Inline
body\epsilon

expansion factor

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The discharge coefficient 

LaTeX Math Inline
bodyC_d
 is a function of a choke narrowing ratio 
LaTeX Math Inline
body\beta
and Reynolds number 
LaTeX Math Inline
body{\rm Re}
 in the pipe:

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C_d = C_d(\beta, {\rm Re})

where

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{\rm Re} = \frac{v \cdot D}{\nu} = \frac{4 \, q}{\pi \, D \, \nu}

where

LaTeX Math Inline
body\nu

kinematic viscosity

LaTeX Math Inline
bodyv

cross-sectional average flow velocity in a pipe


It can be estimated for popular popular choke types or tabulated in laboratory.

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C_d = C_{d, \infty}(\beta) + b(\beta) \cdot 0.5961 + 0.0261 \cdot \beta^2 - 0.216 \cdot \beta^8 + 0.000521 \cdot \left( \frac{ 10^6 \, \beta }{ {\rm Re}}^{-n}

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LaTeX Math Inline
bodyC_{d, \infty}

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LaTeX Math Inline
bodyb

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LaTeX Math Inline
bodyn

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 \right)^{0.7}


See also

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Physics / Fluid Dynamics / Pipe Flow Dynamics / Pipe Flow Simulation (PFS) / Pipeline Choke @model

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