Chapter 9 measurement and theory, 1 speed of sound and gas composition, Chapter 9 – INFICON Composer Elite Gas Concentration Monitor User Manual
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Composer Elite Operating Manual
Chapter 9
Measurement and Theory
9.1 Speed of Sound and Gas Composition
The speed of sound,
C
, in an ideal gas is equal to:
[1]
where:
= 1.4 for Air
[2]
T
= Kelvin temperature
R
= Universal Gas Constant = 8.3143 x 10
7
erg/(Mole K)
M
= Molecular Weight (AMU)
Equation [1] may be expanded for binary mixtures by modifying the Specific Heat
Ratio and molecular weight to account for the Mole Fraction of component two,
x
,
as follows.
[3]
[4]
So the speed of sound of the mixtures,
CM
, is:
[5]
which holds for any ideal mixture; that is, a mixture that is formed without change
in volume.
C
RT
M
----------
=
C
p
C
v
------
Heat Capacity at Constant Pressure
Heat Capacity at Constant Volume
---------------------------------------------------------------------------------------
=
=
1
x
1
1
–
--------------
1 x
–
2
1
–
--------------
+
1
–
+
=
M
xM
1
1 x
–
M
2
+
=
C
M
RT
M
----------
=