Paul V. Marrone

Chemical Relaxation with Preferential Dissociation from Excited Vibrational Levels

The rate of molecular dissociation behind strong shock waves is calculated with the assumption that dissociation can occur preferentially from the higher vibrational levels. An exponential probability of dissociation from the various vibrational levels is employed using an anharmonic oscillator model. Results for the dissociation of oxygen in an argon diluent are presented. Vibrational non‐equilibrium introduces a T−3 temperature dependence into the oxygen dissociation rate constant in the range 4000°–8000°K. A dissociation lag‐time of the order of the extrapolated vibrational relax ation time is predicted immediately behind the shock front. The computed results are shown to be in agreement with available experimental results.

Correspondence between Normal‐Shock and Blunt‐Body Flows

An approximate solution for coupled, nonequilibrium chemistry along streamlines of inviscid, blunt‐body airflows is described. The solution is derived from a correspondence between the chemical relaxation zone along a streamline and that behind a normal shock. This correspondence applies in general for Newtonian flows with binary kinetics. Along the stagnation streamline, binary kinetics are not required. The approximate solution is compared with exact numerical solutions of the blunt‐body problem and is found to be accurate for the high enthalpies corresponding to hypersonic flight.

Viscosity of Dissociated Gases from Shock‐Tube Heat‐Transfer Measurements

Measurements of the heat transfer from dissociated oxygen to the sidewall of a shock tube have been made over a wide range of operating conditions using the methods of thin‐film thermometry. Numerical solutions of the equilibrium shock‐tube wall boundary layer equations for several values of the Lewis number have been obtained. The results show the heat transfer to be very weakly dependent upon the Lewis number. This fact indicates the shock‐tube wall boundary layer to be a source for experimental determinations of the viscosity coefficient of dissociated gases. Experimental data obtained in the equilibrium boundary layer regime agree with the theory at the low temperatures, and rise above the theoretical curves at the higher temperatures. This difference between theory and experiment is attributed to the uncertainty in the calculated viscosity coefficient used in the theory. The experiments were then used to determine new values for the viscosity coefficient of high temperature, dissociated oxygen. These...

Thin-Film Thermometer Measurements In Partially Ionized Shock-Tube Flows

A technique was developed for dealing with the production of spurious electrical signals by partially ionized shock-tube flows in the output of platinum-film resistance thermometers. It involves coating the platinum element with SiO by evaporation and converting this coat to SiO2 by fining. Voltages achieved across this SiO2 film (800 to 1000 A thick) indicate breakdown potentials of approximately 1000 kv/cm. Thermometers with and without such films were tested in argon at shock Mach numbers up to 14: the surface temperature rise of the shock tube sidewall was measured after passage of the shock wave. The thermometers with films exhibited excellent agreement with the theoretical curve, while the results for those without films dropped below the theoretical curve for Mach numbers above 7. Excellent results in air and oxygen were also observed for Mach numbers up to 15. No erosion of the SiO2 films was detected. Foils of metals like gold could be applied directly over such films; this can be used for studies of surface chemistry effects on heat transfer.

Measurement of atomic nitrogen and carbon photoionization cross sections using shock tube vacuum ultraviolet spectrometry

Spectrally resolved vacuum ultraviolet radiation measurements of the continuum arising from the recombination of electrons with N+ and C+ ions have been made using a high-purity shock tube to generate the radiating source. Mixtures of neon and nitrogen or carbon monoxide were used as the test gas, with the radiation observed behind the reflected shock at temperatures of 12,500–13,000°K. Experiments were performed wherein the shocked gas ranged from optically thin to blackbody conditions, from which photoionization cross sections for both N and C were obtained between 700 A and 1100 A. In this wavelength range, the use of windows is precluded. The attendant problems and unique features of the instrumentation designed for these experiments are described. They include a multi-channel spectrometer and an explosively driven windowless plunger which couples the spectrometer to the shock tube. The measured cross-section values are compared with other available experimental values and theoretical predictions. Agreement in the results for nitrogen is taken to validate the technique. No other experimental values were found for carbon, where the measurements yield a cross section approximately twice that obtained from theoretical calculations.

Nitric oxide radiation in the near I.R. spectrum of shock-heated air

Abstract Quantitative spectroscopic measurements have been made of the infrared spectrum of shock-heated air and nitrogen between 0·9 and 1·3 μ. The measurements for air were obtained in the reflected shock region of a shock tube, covering the temperature range 6500–7200°K. The nitrogen data were obtained behind incident shock waves for temperatures between 4600–5700°K, and in the reflected shock region for temperatures from 6800–7500°K. In a previous study it was shown that air radiates much more significantly than nitrogen in this spectral range, and that the radiation could be attributed to transitions between excited electronic states of the nitric oxide molecule. The present measurements confirm these results and also show that the observed excitation energy of the radiation is inconsistent with energy levels in nitrogen. The data from both studies are reviewed, and it is concluded that the NO hypothesis is consistent with the experimental evidence.