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Vibrational relaxation in oxygen and nitrogen

Published online by Cambridge University Press:  28 March 2006

Vernon Blackman
Vernon Blackman
Affiliation:
Palmer Physical Laboratory, Princeton University
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Abstract

A converging channel of area ratio 34 : 1 has been developed to produce strong shock waves in a tube. Shock waves of speeds M1=3−7·5 in oxygen and M1 = 5−10 in nitrogen have now been studied with an interferometer, and values of the relaxation time τ for the approach to vibrational equilibrium behind the shocks have been measured. The value of τ (atmospheric) varies from 54μsec at 800° K to 1·3 μsec at 3000° K for oxygen and from 19 μsec at 3500° K to 5 μsec at 5500° K for nitrogen. For oxygen, the graph of log τ against T−1/3 is not quite the straight line predicted by the Landau-Teller theory. The density ratios across the shocks were measured and compared with values calculated by the Bethe-Teller method for variable specific heats. Agreement between the measured and calculated values is satisfactory. Experiments were also performed on oxygen-nitrogen mixtures to determine the effect of nitrogen on the approach to equilibrium of the oxygen. It was found that O2 and N2 collisions at approximately 2000° K are 40% as effective in transferring energy to the oxygen as O2 and O2 collisions. A device that detects a shock with a time lag of less than 1μsec, consisting of an evaporated gold film which changes its resistance when heated by the shock, was also developed.

Information

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 1 , Issue 1 , May 1956 , pp. 61 - 85
Copyright
© 1956 Cambridge University Press

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