INFICON Composer Elite Gas Concentration Monitor - Manual (Page 135)

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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
---------- =