Flow-X─ Function Reference
4-123
Flow-X General functions - fxAPI_RD60F_NGL_LPG
The following range checks
apply:
For lower range:
0.350 <= RD60 < 0.425
-50 to (695.51*RD60 -
155.51) °F
Higher range:
0.425 <= RD60 <= 0.676
-50 to 140 °F
with RD60 being the relative
density at 60°F
Calculations
The calculations depend on the conversion method.
Conversion method 1: from observed to standard conditions.
The function performs the following iterative algorithm to calculate the relative density at 60
°
F and
the equilibrium pressure.
1.
When API 11.2.4 rounding is enabled, the input relative density and temperature
values are rounded in accordance with the standard
2.
At the start of the iteration the relative density at [60
F, equilibrium pressure] is
set equal to the observed relative density and the CPL value is set to 1.
3.
First the relative density corrected for pressure is calculated by dividing the
observed relative density by the CPL value.
4.
The CTL value and the relative density at [60
F, equilibrium pressure] is
calculated from the relative density corrected for pressure and the observed
temperature according to Table 23E
5.
Depending on the value of input 'Equilibrium pressure mode', either value of
input 'Equilibrium pressure value' is used or the equilibrium pressure (vapor
pressure) is calculated according to GPA TP-15. Whether the GPA TP-15 rounding
and truncation rules are applied is dictated by input ‘GPA-TP15 rounding’
6.
The compressibility factor F is calculated according to API MPMS 11.2.2 from the
relative density at [60
F, equilibrium pressure] and the 'Observed temperature',
with, depending on input API 11.2.2, rounding and truncation according to the
standard.
7.
The CPL value is calculated from the compressibility factor, the equilibrium
pressure and the 'Observed pressure' input value.
8.
The new value for relative density at [60
F, equilibrium pressure] is calculated by
dividing the observed density by the CTL and CPL values.
9.
Steps 3 though 8 are repeated taking the density value from step 8 as the staring
value until the absolute difference between two consecutive density values is
less than the convergence limit.
To avoid convergence problems different convergence limits are applied,
depending on the whether API 11.2.2 and/or GPA TP-15 rounding is applied:
If API 11.2.2M rounding is enabled
-> Limit = 0.00005 kg/m3
else if GPA TP-15 rounding is enabled -> Limit = 0.000005 kg/m3
else
-> Limit = 0.00000001 kg/m3
10.
If API 11.2.4 rounding is enabled, then the relative density at [60
F, equilibrium
pressure] is rounded to 0.0001
Summary of Contents for flow-x
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