Table Of ContentThe Pennsylvania State College
The Graduate School
Department of Physics
Ultrasonic Absorption
in Gases
A dissertation
by
Prank Tobias Dietz
Submitted in partial fulfillment
of the requirements
for the degree of
Doctor of Philosophy
August 1951
Approved
Department of Phyaics
epartment
Acknowledgement
The writer wishes to express his thanks and in
debtedness to Drso Wo Ho Pielemeier and Ro Simon, whose
interest and guidance made this work possible, and to
Mr» P, Wo Jackson for his help with many of the elec
trical and mechanical detailso
Table of Contents
Page
Introduction 1
Theory 7
Equipment 11
The Gases 20
Method of Measurement 22
Results 2*+
02-H20 2b
o2~NH3»H2o 3*+
n2-C02 39
A.-C02 U-1*
Conclusions b7
Appendix *+8
References 52
List of Figures
Figure Page
1. Photograph of the apparatus 12
2. Photograph of the apparatus 13
3* Photograph of the apparatus l1*
*+. Block diagram of the transmitter
circuit 17
5. Block diagram of the receiver
circuit 17
6. mrp for C^-H^O mixtures vs. frequency 28
7-12. for mixtures vs, frequency 29-31
13- fmax for O2 vs, absolute humidity 32
I1*. log fraax for C>2 vs. log of absolute
humidity 33
l?. nip for mixtures vs. frequency 38
16. mC02 VSe fretTuency *+2
17. mC02 vs<’ concen‘t:ra'tion C02 in W2 ^
18. nip for argon-CO^ mixtures vs. frequency *+6
19. Sound amplitude vs. position 51
lo
T ntroductlon
With the limitations of the experimental aDparatus in
mind, the following problems were undertaken.. The effects
of water vapor and ammonia gas on the relaxation times of
oxygen were investigated, and the sound absorption in mix
tures of nitrogen and carbon dioxide and argon and carbon
was measured,,
It was found after considerable preliminary investi
gation that consistent results could not be expected when
measurements were made using gases or mixtures of gases in
which the attenuation of sound was small. This is due to
the fact that the method used to determine the absorption
coefficient requires that the anuaratus be calibrated by
means of a gas in which the attenuation is known or is
small enough to be neglected. Nitrogen is such a gas.
Its absorption coefficient is small in the frequency range
covered by this work, viz., 20-110 kc. Since the attenu
ation in N2 must, be subtracted from that measured in a gas
under test, it becomes evident that the test gas should have
an attenuation substantially different from that of N2 „
On the other hand, the attenuation cannot be too greats
The absorption coefficient of a gas such as nure C02 cannot
be measured over the whole frequency range mentioned above,
C02 has a large absorption coefficient and difficulty occurs
2 o
fi'ifi t.n the? fac.t that the signal-to-riol se ratio becomes small
quite racidlv as the distance between the source and receiver
is increased and the arrmlifier gain is increased,, Thl s situ
ation becomes progressively worse with Increasing: frequency3
The mixtures and 0^~rTH~ presented absorption co-
- * 3
efficients which lav between the extremes mentioned abovec
The mixtures A-COo and No-CC^ bordered on the high absorp~
tion extreme0
The effects of water vapor and ammonia on the relax-
atlon times of oxygen have been investigated by Kneser and
Knudsen^®) , Knudsen and 0b o r t ^ 3 .)? Oberst^?), and Knotzel^^
Tn addition Schmidtmuell er(2*+) published some absorption data
on 02”H20 mixtures0
Kneser and Knudsen (193*0 investigated the behavior of
these mixtures in the audible frequency range up to approxi
mately 9 kc«. using a reverberation method , This involves the
measurement of the decay time of a sound pulse in the test
chamber, and was not useable for frequencies ahove approxi
mately 10 kc „ since rates of decav become too rapid.,
Knudsen and Obert (1916) measured sound absorption in
these mixtures, extending the frequency range to 3*+ k c0 by
means of a new experimental technlqueo A magnetostrictive
generator supplied acoustic energv to a chamber at a known
rate, The sound was mechanically diffused and the intensity
of the sound was measured by means of a crystal microphone,
3.
These facts, together with 1rformat1 on apout wall absorp
tion and measurements with a gas of known absorption, were
sufficient to allow a determination of the sound absorp
tion in the gas under test- This method may admit a prob
able error as large as 301,
Oberst (1937) made preliminary measurements in the
audible range using a resonance tube method- This method
■»
was taken over >■> Knot, ^elf lln'h s who refined it and made
a series of careful measurements of absorption in C>2“H20
and 02-^3 mixtures in the audible range up to 5 kc-
In connection with the effects of water vapor on the
absorption of sound in oxygen, Schmidtmueller (1938) re
ported some absorption data obtained from measurements of
the sound field radiate! into an absorbing chamber by a
magnetos tri ctive rod- Measurements were made in the fre<=
quencv range 20-100 kc-
Kendie(7) (1938) measured the molecular absorption of
oxvgen-water vapor mixtures at temperatures around 0 to
50OG- at 11 ? 98, 127 o and 281+ kc„ b,r means of an acoustic
interferometer- he found that maximum absorption occurred
?t a higher percent concentration than that found bv Knud
sen and Obert^^J for the lower frenuenciee.
All these researches indicated that the effect of water
vapor on oxygen was unloue- The relaxation time was found
to depend predominantly uoon the square of the water vapor
L+.,
concentration. The relax,- ti on time for oxygen in the oxygen-
ammonia mixtures was found to have a linear dependence upon
the ammonia concentration.
With the discovery by Pierce ^ ^ U n 1925 that CO2 showed
a large amount of acoustic absorption, a large number of work-
ers have explored the subject. Rich and Pielemeier*-22)(1925)
using a quartz crystal sound source and a radiometer were
able to show that the absorption of sound in air increased
with increasing CO2 content, Abello^^^) (1928) investi
gated the absorption of CC^-alr mixtures at a frequency of
612 kc, The sound from a quartz crystal passed through an
absorption chamber and was measured, in his earlier work, by
means of a torsion radiometer, and later by a second crystal..
P i e l e m e i e r (1929) made measurements on CO2 and air using
an acoustic interferometer. Measurements were made in the
frequency range from 300-1M-00 kc „ The absorption of sound
by CC>2 was found to increase with frequency with the CO2 be
coming practically opaque at l*fOO kc. Pielemeier also noted
the marked effect of humiditv on the absorption of sound in
CO^. Grossman^) (1932) devised a method using two quartz
crystals i*- a gas chamber, for measuring sound absorptions
in the frequency range 30-300 kc. He found that tne absorp
tion coefficient for 00^ was strongly frequency deoendent,
He also found a molecular absorption peak at 100 kc, Hub-
bard^^(1932) published a paper dealing with the acoustic
5*
Interferometer and gave a few absorption data for C02 and
air measured at a frequency of 597 kc.
Pielemeierd?) ( 1932) reported on sound absorption in
CO2 at relative humidities ranging from 21+-31^ in the fre
quency range from 300-2000 kc. A sharp absorption peak was
found at 217 kc0
Leonard (ll+) (19k0) measured the absorption of sound
in CO2 by a direct method, A microphone responding to the
sound pressure was moved away from a niston source. He
found a peak absorption for CO2 at 30 kc. He also reported
on sound absorption in N2-C02 mixtures,
Fricke^) (IQWO) measured sonic absorption in C02 at
frequencies between 8 and 130 ke„ His experimental scheme
was similar to that already described in connection with the
work of Knudsen and 0bert^3)o Fricke showed that for dry
C02 the peak absorption occurred at 20 kc 0 and that
had a value of 0 „230o
Knudsen and Fricke^^) (19L0 ) using an improved appa~
ratus based on that described in their 1938 paper report on
the effect of impurities on the absorption of sound in C02,
They found that 1% of H20 vapor caused a shift of 2250 kc,
in the absorption band for C02«, It was also found that the
frequency for maximum absorption varied linearly with the
percent of water vapor.
6.
Pielemeier, Saxton, and Telfair^20^, Telfair^2<^ , and
Pielemeier and 3 y e r s ^ ^ (lPM-O—l P ^ ) have reported on the
effects of humidity on the absorption of sound in CC^o
Pielemeier ^ ^ (19*+3) presented a review of ultrasonic
measurements in C0^9
The purpose of my work is to investigate the effects
of water vapor and ammonia gas on the relaxation time in
oxygen and to make measurements of sound absorption in
nitrogen-carbon dioxide and argon-carbon dioxide mixtures*
