MKS Mass-Flo 2179A - How To Calculate the GCF for Gas Mixtures

The Gas Correction Factor (GCF) Cha
p
ter Three: Overview
36
How To Calculate the GCF for Gas Mixtures
For gas mixtures, the calculated Gas Correction Factor is not simply the weighted average of
each component’s GCF. Instead, the GCF (relative to nitrogen) is calculated by the following
equation:
GCF
M
11 22 nn
11 1 22 2 nn n
=
(0.3106) (a s + a s + ...a s )
(a d cp +a d cp + ...a d cp )
where:
GCF
M
= Gas Correction Factor for a gas mixture
0.3106 = (Standard Density of nitrogen) (Specific Heat of nitrogen)
a
1
through a
n
= Fractional Flow of gases 1 through n
Note
: a
1
through a
n
must add up to 1.0
s
1
through s
n
= Molecular Structure correction factor for gases 1 through n
where S equals:
1.030 for Monatomic
g
ases
1.000 for Diatomic
g
ases
0.941 for Triatomic
g
ases
0.880 for Pol
y
atomic
g
ases
d
1
through d
n
= Standard Density for gases 1 through n, in g/l
(at 0° C and 760 mmHg)
cp
1
through cp
n
= Specific Heat of gases 1 through n, cal/g° C
Note
The values for s, d, and cp
x
are available for most gases, refer to
Appendix C: Gas Correction Factors
, page 65.
The values for a
1
through a
n
(which must add up to 1.0) are application
dependent.