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Flow-X─ Function Reference
Flow-X General functions - fxISO5167_Orifice
Where:
p
1
Pressure at upstream tapping [bar(a)]
p
2
Pressure at downstream tapping [bar(a)]
p
3
Fully recovered downstream pressure [bar(a)]

p Differential pressure [mbar]
p
LOSS
Pressure loss over the meter [bar]
Temperature correction

When input 'Temperature correction' is set to 1, then an isentropic expansion based on the
isentropic coefficient is applied:
 
15 . 273 15 . 273
1
2
3
3 2







  



p
p
t t
 
15 . 273 15 . 273
1
1
3
3 1







  



p
p
t t

When input 'Temperature correction' is set to 2, then an isentropic expansion based on
input 'Temperature exponent' is applied:
 
15 . 273 15 . 273
2
3
3 2







  
TE
K
p
p
t t
 
15 . 273 15 . 273
1
3
3 1







  
TE
K
p
p
t t

When input 'Temperature correction' is set to 3, then an isenthalpic expansion based on the
linear Joule Thomson correction as defined in ISO5167-1:2003, taking input 'Temperature
exponent' as the Joule Thomson coefficient:
 
JT
p p t t

   
2 1 2 1
 
JT
p p t t

   
3 1 3 1
Where:
t
1
Upstream temperature °C
t
3
Downstream temperature °C
p
1
Upstream pressure bar(a)
p
3
Fully recovered downstream pressure bar(a)

Isentropic exponent -
K
TE
Temperature exponent -

JT
Joule Thomson coefficient °C/bar
ISO-5167 edition 2003 prescribes an isenthalpic expansion instead of an isentropic expansion. This can
be achieved by assigning a fixed Joule Thomson coefficient to input 'Temperature Exponent'.
Note: ISO is working a method to calculate the Joule Thomson rather than using a fixed value.