Liquid Controls SP4000 - Manual (Page 102)

99
SP4000 Flow Computer
7.3.4
Density/Viscosity
Computation
(continued)
7.3.5
Corrected
Volume Flow
Computation
Viscosity (cP) Computation:
Liquid Case NOTE:
B viscosity (in cP)
cP viscosity = A • exp
Viscosity cS =
flowing density
( Tf + 459.67) density of water @ 4
°
C
Gas Case
cP viscosity = A • ( Tf + 459.67) B
Steam Case
cP viscosity = f(Tf, Pf)
Corrected Volume Flow Computation:
Liquid Case
std. volume flow = volume flow • ( 1 - Therm.Exp.Coef. •( Tf - T
ref
)) 2
Gas Case
std.volume flow = volume flow • Pf
.
• (T ref
+ 273.15) • Z
ref
.
P
ref
( Tf + 273.15) Zf
NOTE: For Natural Gas:
Z
ref
.
Z
f
is determined by NX-19 when this selection is supplied and selected.
Natural Gas NX-19 Equation: The NX-19 (1963) natural gas state equations are widely used
in custody transfer applications. Over most normal measurement ranges, 500 to 5000 psia
(3.5 to 10.4 MPa) and -10 to 100
°
F (-23 to 38
°
C), the NX-19 equation will compute the gas
compressibility factor to within 0.2% of the values computed by the newer AGA-8 state
equation.
The ranges over which the NX-19 equation applies are:
Pressure P
G
To 5000 psig (10.34 MPa gauge)
Temperature T
f
-40 to 240
°
F (-40 to 116
°
C)
Specific Gravity G 0.554 to 1.0
CO
2
and N
2
0 to 15%
Our Flow Computer uses the Specific Gravity method to first obtain the adjusted temperature
and pressure before entering the state equation. This method calculates the adjusted pres-
sure and temperature from the mole fractions of carbon dioxide and nitrogen as
P
adj
=
156.47 P G .
psig
160.8 – 7.22 G
g
+ 100 X
C02
– 39.2 X
N2
Where X
C02 and
X
N2
are the mole fractions of carbon dioxide and nitrogen, respectively. The
adjusted temperature is defined by
T
adj
=
226.29 (T
F
+ 460) °
F
99.15 + 211.9 G
g
– 100 X
C02
– 168.1 X
N2
( )