4-14
1010GCNFM-3C
Section 4
4.3.1 BASE TEMP and BASE PRES. PSIA
The base temperature and base pressure represents the conditions to which the reported volumetric
flow rate and volumetric total will be compensated to (standard or normal con-ditions) as described in
the equation below. The required units for data entry are determined by the [Preferred Units] menu cell
(English or Metric) selected in the Meter Facilities menu. If Metric units are selected then the units for
temperature and pressure will be degrees Celsius and BARA (absolute) respectively. For English units,
temperature and pressure will be in degrees Fahrenheit and PSIA.
Qbase = Qact
P
act
Pbase
T
base
Tact
Z
base
Zact
where: Q = Volumetic flow rate
P = Pressure (absolute)
T = Temperature (absolute)
Z = Compressibility
base = Base conditions (pressure and temperature)
act = Actual flowing condition (pressure and temperature)
4.3.2 SPEC. HEAT RATIO
The specific heat ratio refers to the ratio of the gas specific heat at constant pressure to specific heat at
constant volume. This ratio (along with the measure gas temperature and sonic velocity) allows the flow
computer to compute (dynamically) the average specific gravity of the gas. The default value of 1.3 is
suitable for most gases, but should be modified if this value is known for your specific application.
4.3.3 VISCOSITY (cP)
The absolute gas viscosity (along with the measured gas density and raw flow velocity) is used by the
flow computer to compute the instantaneous Reynolds number. The Reynolds number is then used to
derive the correction factor the required flow profile compensation.
The expected units for viscosity is “centipoise”. The default value of 0.01 is suitable for most gases, but
should be modified if this value is known for your specific application.
GAS PARAMETERS MENU STRUCTURE AND DEFAULTS
Gas Parameters Base Temp 60
o
F (15.5
o
C) Enter reference temperature in C or F.
Base Pres. PSIA 14.7 psia (1.014 bara) Enter reference pressure in PSIA or BARA.
Spec. Heat Ratio 1.3 Enter gas specific heat ratio (constant pressure to con-
stant volume.)
Viscosity (cP) 0.010 centipoise Enter absolute gas viscosity in centipoise.
Fixed MW g/mole 0.0 grams/mole Enter fixed molecular weight to override automatic com-
putation.
Estimated Vs m/s 450 m/sec Enter the nominal sound velocity of the gas if signifi-
cantly different from this default.
Fixed Pres. PSIA 14.7 psia (1.014 bara) Enter fixed operating pressure if external input is not
available.
Z Base 1.000 Enter the compressibility factor for the gas at base con-
ditions.
Z Actual 1.000 Enter fixed compressibility factor where pressure, tem-
perature and gas compostition do not vary significantly.
AGA8 Comp YES/NO If a valid AGA8 table is installed (see para. 4.3.9) then
select [YES] to activate the AGA8 compensation (Std.
Vol. Comp from the Flow/Total Units menu must also be
selected).
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