Measurements of vibrational relaxation and dissociation of oxygen with laser absorption spectroscopy with applications for energy transfer in nonequilibrium air
- The vibrational relaxation times of oxygen were measured using laser absorption spectroscopy behind incident and reflected shocks in a shock tube. The Bethe-Teller equation was used to model the vibrational relaxation, which along with the shock jump relations were used to model the gasdynamic conditions throughout the nonequilibrium relaxation process. The absorbance was modeled based on these gasdynamic conditions while adjusting the vibrational relaxation time to fit the model to the measured oxygen absorbance time-history at wavelengths 210 - 230 nm in the Schumann-Runge system. Undiluted oxygen was studied behind incident shocks at initial post-shock translational/rotational temperatures from 1000 - 3300 K and pressures from 0.05 to 0.7 atm while a mixture of 2% oxygen in argon was studied behind incident and reflected shocks at initial translational/rotational temperatures from 1000 - 4000 K and pressures from 0.2 to 1 atm. Good agreement was found with prior experimental work by White and Millikan, Losev and Generalov, and Camac, though the current relaxation time data have less scatter and reduced uncertainty. The current results are also in excellent agreement with the well-known relaxation time recommendations of Millikan and White. The dissociation rate coefficient for oxygen in argon, O2 + Ar < => O + O + Ar, was measured using laser absorption near 216 nm in the Schumann-Runge system in a shock tube. A mixture of 2% oxygen in argon was studied behind reflected shocks at initial equilibirum temperatures from 4400 - 7900 K and pressures from 0.2 to 1 atm. The dissociation was modeled de-coupled from vibrational relaxation, as dissociation was evident only after the test gas mixture was near vibrational equilibrium. The dissociation rate coefficient was determined by fitting the measured oxygen absorbance time-history for each experiment using temperatures based on the incident shock speed and the shock relations and adjusting the A-factor of the dissociation rate coefficient. Good agreement was found with the prior experimental work and model of Camac and Vaughan. Consistent results were also obtained for measurements with constant pressure as well as increasing pressure, validating our method to account for pressure changes by including the pressure profile in the dissociation model.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Mechanical Engineering.
|Statement of responsibility
|Submitted to the Department of Mechanical Engineering.
|Thesis (Engineering)--Stanford University, 2014.
- © 2014 by Kyle Graham Owen
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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