Relates pressure drop on the choke with $\begin{array}{l}p_{out} - p_{in}\end{array}$ the flowrate through the choke $\begin{array}{l}q\end{array}$ :

(1)	$\begin{array}{l}\displaystyle p_{out} - p_{in} = \frac{\rho}{8.05 \, d^4_D \, C_D^2} \ q^2\end{array}$

where

$\begin{array}{l}\rho\end{array}$	fluid density
$\begin{array}{l}d_D\end{array}$	choke diameter
$\begin{array}{l}C_D\end{array}$	choke coefficient (see (2))
$\begin{array}{l}d\end{array}$	internal diameter of the incharge/discharge pipe
$\begin{array}{l}{\rm Re}\end{array}$	Reynolds number

(2)	$\begin{array}{l}\displaystyle C_D = \frac{d_D}{d} + 0.3167 \, \bigg( \frac{d}{d_D} \bigg)^{0.6} + 0.025 \ \big [ \log {\rm Re} - 4 \big ]\end{array}$

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See also