Date of Award

Spring 1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Surendra N. Tiwari

Committee Member

Allan J. Zuckerwar

Committee Member

Gennaro L. Goglia

Committee Member

Wynford Harries

Abstract

This study was motivated by a need to obtain standard values of nitrogen's contribution to sound absorption in the Earth's atmosphere. Specific goals included accurate measurements of sound absorption in nitrogen - water vapor mixtures at room temperature and low frequency/pressure ratios, the determination of the N2 vibrational relaxation peak location, (f/P)max, on the f/P axis as a function of humidity, h, and critical evaluation of all results.

The free decay technique was used in a resonance tube to obtain ten sets of sound absorption data in N2-H2O gas mixtures and requisite companion data in N2-CO2 and technical grade N(,2). All measurements were made at an ambient temperature of 297 K. The N2-H2O mixture pressures range from 1 to 85.5 atm, water vapor content ranged from 2.5 to 18800 ppm (2.5 x 10-6 to 0.0188 mole fraction), and the f/P range was 0.1 to 2500 Hz/atm.

A best-fit, linear relationship between (f/P)max and h yields a correlation coefficient of 0.9938, an intercept of 0.013 +/- 0.012 Hz/atm, and a slope of (2.00 +/- 0.24) x 104 (Hz/atm)/mole fraction. For this case, a vibration-translation energy transfer model was initially assumed. The basic slope is significantly lower than the value of 2.6 x 10('4) (Hz/atm)/mole fraction reported by Chang, Shields, and Bass (also a V-T model) at higher temperatures and humidities, but both sets of data are shown to be mutually consistent by a model in which vibration-vibration energy transfer is assumed to dominate the relaxation path. The best fit of this model to both sets of data yields an intercept of 0.013 Hz/atm and a slope of 2.0 x 104 h x {(1 + 173h)/(1 + 133h)}, (Hz/atm)/mole fraction.

Both models (V-T and V-V) were evaluated with respect to theory and experiment to ascertain the better model. Theoretical transfer rates for the models were calculated, using formulations of Tanczos and Shin - Nagel and Rogovin, and then compared to corresponding transfer rates derived from experimental results and, also, with one another (as appropriate). From the theoretical calculations, the V-V transfer rate is seen to be 4 to 6 orders of magnitude faster than the V-T rate. This result and the other evidence provide strong support for the V-V model; hence, it is preferred.

Good agreement is found between the present experimental result of 1.26 x 105 (s+atm)-1 at 297 K and a N2) -H2O V-V transfer rate value of 1.77 x 105(s+atm)'-1 at 300 K obtained by use of the Nagel and Rogovin theory. Also, the present experimental result shows favorable to good agreement with recent experimental results obtained by nonacoustical methods.

The dipole - induced-dipole interaction between the H2O and N2 molecules is found to be negligible.

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DOI

10.25777/e0sv-4654

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