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Flow Through Orifice Plates in Compressible Fluid Service at High Pressure Drop
Nov 08 2010 01:40 PM | dkirk in Safety and Pressure Relief![](http://www.cheresources.com/invision/uploads/03058a3fe6abb4d3a547a72a7c514722.jpg)
Orifice flow calculations typically use the following equations or some variant of them:
![]() | Crane Eq. 2-24 / Eq. (1) |
![]() | Crane Eq. 2-23 / Eq. (2) |
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For metering applications the ASME equation is often used to determine the Expansion Factor Y:
![]() | Eq. (3) |
for flange taps, where P and T are in absolute units.
For high accuracy metering (e.g. AGA 3) use of these calculations is often limited to .
![]() | Eq. (4) |
where P and T are in absolute units.
It is then often assumed that the orifice flow goes critical (i.e. sonic velocity) at P2 = 0.528 x P1 (for air) and the choked flow equation is then applied:
![]() | Eq. (5) |
![]() | Eq. (6) |
(Crane Pg 2-15), where Pcr = 0.528 x P1
For P2 less than Pcr this method assumes that the flow does not increase further.
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