User guide

9 - 1
PN 074-566-P1B
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,
C
M
, 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–
--------------
1x–

2
1–
--------------+
1–
+=
MxM
1
1x–M
2
+=
C
M
RT
M
----------=