Chapter 6: Gas Correction Factor (GCF)
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Chapter 6: Gas Correction Factor (GCF)
The Gas Correction Factor (GCF):
A Gas Correction Factor (GCF) is used to indicate the ratio of flow rates of different gases which
will produce the same output signal from a mass flow meter / controller. The GCF is a function of
specific heat, density, and the molecular structure of the gases. Nitrogen (N2) is normally used as
the baseline gas (GCF = 1) since flow meters and controllers are usually calibrated with nitrogen.
GCF (N2) = 1
Appendix C lists the gas correction factors for many commonly used pure gases. If the gas you
are using is not listed in there, you must calculate its GCF. The equations for calculating gas
correction factors are described below.
How To Calculate the GCF for Pure Gases
To calculate the Gas Correction Factor for any pure gas (X), use the following equation:
xx
x
cp
s 0,3106
GCF
∗
∗
=
ρ
where:
GCF
x
= gas correction factor for gas X
0,3106
= (standard density of nitrogen) • (specific heat of nitrogen)
s = molecular structure correction factor where S equals:
1.030 for monoatomic gases
1.000 for diatomic gases
0.941 for triatomic gases
0.880 for polyatomic gases
d
x
= standard density of gas X, in g/l (at 0° C and 1013,25 mbar)
cp
x
= specific heat of gas X, in cal/g° C
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