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Showing papers on "Shock tube published in 1970"


Journal ArticleDOI
TL;DR: In this paper, a gas mixture is introduced into the nozzle chamber and outside the shock barrel, this aspiration acts very selectively on the light molecules, and a mixture enriched in lighter species is attainable by skimming the free jet.
Abstract: The shock wave system of the underexpanded free jet, in a region where the pressure is in the range of 10−2 up to 1 torr, is partly invaded by background molecules, these latter being pumped and carried by the supersonic flow. When a gas mixture is introduced into the nozzle chamber and outside the shock barrel, this aspiration acts very selectively on the light molecules, and a mixture enriched in lighter species is attainable by skimming the free jet. This new aerodynamic separation effect, which is applicable to isotopic mixtures, is very strong in comparison to the efficiency of an elementary gaseous diffusion membrane.

82 citations



Journal ArticleDOI
TL;DR: In this article, the authors measured the relaxation times of CO2 in an atmosphere of N2, Ne, He, D2 and H2 and showed that during the approach to equilibrium the relaxation time changes in the way to be expected from the change in the translational temperature.
Abstract: times and that during the approach to equilibrium the relaxation time changes in the way to be expected from the change in the translational temperature. These observations have been confirmed by infrared measurements on shock heated CO2 (Hodgson & line i969) and are consistent with recent laser fluorescence measurements on the rate of deactivation of the asymmetric stretching mode (Hocker, Kovacs, Rhodes, Flynn & Javan i966; Moore, Wood, Ho & Yardley i967). In the present paper results are given for the relaxation times of C02 in an atmosphere of N2, Ne, He, D2 and H2. The object of these experiments was to measure relaxation times over a wide range of temperatures for these collision partners. The results give some insight into the relative importance of the effeets of the reduced masses and force fields at different temperatures. They provide the grounds for testing current calculations of relaxation times and help in the understanding of the collision processes important in the CO2 laser.

58 citations




Journal ArticleDOI
TL;DR: In this paper, a single-pulse burst tube was used to pyrolyze 4-methyl-l-pentyne in a singlepulse shock tube and the decomposition process involved bond breaking and molecular reaction.
Abstract: Dilute mixtures of 4-methyl-l-pentyne have been pyrolyzed in a single-pulse shock tube. The decomposition process involves bond breaking: as well as a molecular reaction: The rate parameters are: The heat of formation of propynyl radical is thus ΔHf300 = 338 kJ mol−1 (80.7 kcal mol−1)˙ This leads to a propynyl resonance energy of 40 kJ mol−1 (9.6 kcal mol−1).

40 citations


Journal ArticleDOI
TL;DR: Carbon dioxide gas dynamic layer in shock tube facility, measuring shape, time, output energy, beam diameter, etc as discussed by the authors, measuring shape and time, time and energy, etc.
Abstract: Carbon dioxide gas dynamic layer in shock tube facility, measuring shape, time, output energy, beam diameter, etc

37 citations


Journal ArticleDOI
TL;DR: Plasma polarization shift for resonance line of ionized He in shock tube due to negative space charge was reported in this article, where negative space charges were assumed to be a Gaussian distribution.
Abstract: Plasma polarization shift for resonance line of ionized He in shock tube due to negative space charge

33 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical analysis of the interaction between normal shock waves and deformable solid materials, with particular reference to the characteristics of the reflected shock wave, is presented, which is of importance in all those cases in which a shock wave impings on solid walls.
Abstract: A theoretical-experimental study has been performed on the interaction between normal shock waves and deformable solid materials, with particular reference to the characteristics of the reflected shock wave. The present study is of importance in all those cases in which a shock wave impings on solid walls (i. e. explosions, sonic booms etc.). The first part presents a theoretical analysis which gives the solution for the shock wave intensity reflected into the gas and for the transmitted shock wave propagating into the elastic solid material for both the cases of linear (Hooke type) and non linear solids. For the first kind of materials a closed form solution is found. For the non-linear materials the problem is solved through a numerical analysis. The experiments concern with two kinds of expanded foams (closed cell and open cell foams). These materials have been selected because of the good deformation and density characteristics which both are necessary to evidentiate the shock wave interaction phenomena. The tests have been performed putting a cylindrical model of the material under study at the closed end of a shock tube and creating shock waves of variable strength which impinge on the material. Slightly upstream of the free end wall of the model, the pressures history is recorded by means of a pressure pick up and of an oscilloscope. The range of the shock wave Mach number has been1,2⩽Ms⩽2,2 with initial pressures ranging between50⩽p 1 ⩽760 mmHg. The theoretical analysis seems to be in a very good agreement with the experiments performed, especially when due account is given to the gap existing between shock tube and model walls.

29 citations


Journal ArticleDOI
TL;DR: In this paper, a check of the data from comparative rate single-pulse shock tube experiments have been carried out through the use of a new standard reaction, the decyclization reaction of ethylcyclobutane.
Abstract: A check of the data from comparative rate single-pulse shock tube experiments have been carried out through the use of a new standard reaction, the decyclization reaction of ethylcyclobutane. The rate expressions for cyclohexene and 2,2,3-trimethylbutane have been found to be in excellent agreement with previously published results. Most of the small discrepancy that does exist is apparently due to the differences between the present and earlier (decomposition of isopropyl bromide) "standard" reaction. For the latter process, the present study yields These results confirm the correctness of previously published comparative rate single-pulse shock tube experiments. They demonstrate once again that for the decomposition of paraffin hydrocarbons, calculated preexponential factors are at least an order of magnitude higher than the directly measured number and that the accepted value of the heat of formation of t-butyl radicals ΔHf300(tC4H9·) = 29 kJ (6.8 kcals) is at least 10 kJ too low. Finally, attention is called to recent studies on neopentane decomposition in flow and static systems which are in complete agreement with the present conclusions.

29 citations


Journal ArticleDOI
TL;DR: In this article, a novel technique has been developed for use in the study of collisional energy transfer and chemical reaction rates in rapidly cooled gases, where the shock heated test gas sample is stationary during the cooling process so that the temporal behavior of a particular nonequilibrium property may be continuously monitored.
Abstract: A novel technique has been developed for use in the study of collisional energy transfer and chemical reaction rates in rapidly cooled gases. The principal feature is that the shock heated test gas sample is stationary during the cooling process so that the temporal behavior of a particular nonequilibrium property may be continuously monitored. The technique has been applied to the measurement of the vibrational de‐excitation rate of carbon monoxide in an argon heat bath, using the fundamental infrared emission band of CO to follow its vibrational temperature throughout the expansion. In contrast to some recent investigations which indicate enhanced vibrational de‐excitation rates, the present experiments show that when translation–vibration collisions control the relaxation process the characteristic vibrational relaxation time of carbon monoxide diluted in argon is the same no matter whether it is measured in a compression (shock wave) or expansion environment.

Journal ArticleDOI
TL;DR: In this article, the thermal stability of sulfuryl difluoride at high temperatures has been investigated and effective first-order rate constants were evaluated from the logarithmic initial slopes of the radiation decay curves.
Abstract: Recent thermal decomposition studies of SF6 have led to interest in its principal oxidation product, sulfuryl difluoride. In the present study the thermal stability of SO2F2 at high temperatures has been investigated. Highly dilute SO2F2–Ar mixtures (∼ 0.1%) were shock heated in a conventional 1.5″ stainless‐steel shock tube. The SO2F2 concentration was monitored as a function of time behind the incident shock wave by its infrared emission at 11.7 μ utilizing a liquid helium cooled Cu:Ge detector. The initial pressure in the shock tube was varied from 30 to 600 torr and the temperature range covered was 1900–2300°K. The monitored radiation was shown to be transparent over the range of densities employed. Effective first‐order rate constants were evaluated from the logarithmic initial slopes of the radiation decay curves. For the 30‐torr data, a unimolecular rate constant fit to the data is keff = 2.1 × 1011exp(− 39 200 / T) sec−1. The data are analyzed in the light of several modern unimolecular rate theo...

Journal ArticleDOI
TL;DR: In this paper, measured thermodynamic conditions behind reflected shocks in a gas-driven diaphragm shock tube are compared to Rankine-Hugoniot predictions, and the consistency of the data indicates that a homogeneous local thermodynamic equilibrium model is an adequate description of the gas.
Abstract: Measured thermodynamic conditions behind reflected shocks in a gas‐driven diaphragm shock tube are compared to Rankine‐Hugoniot predictions. Pressures of the shock‐heated neon, which contained small concentrations of spectroscopic additives, were measured by quartz transducers. Temperatures (9000‐13 000°K) were simultaneously measured spectroscopically by line reversal and absolute emission techniques, while electron densities were measured by the broadening of the Balmer line Hβ. The temperature has been measured to an accuracy of ±1.5%, while electron densities have been determined with an accuracy of ±10%. Pressure measurements attained accuracies of ±5%. The consistency of the data indicates that a homogeneous local thermodynamic equilibrium model is an adequate description of the shock‐heated gas. The state measurements, compared with the real gas Rankine‐Hugoniot predictions, show significant departures. Predicted temperatures are typically 3% ± 10% higher than those measured. The predicted electron...

Journal ArticleDOI
TL;DR: Vibrational relaxation behind incident shock waves in pure nitrogen, using end wall pressure measurements as mentioned in this paper, was shown to be a function of the end-wall pressure measurement of pure nitrogen.
Abstract: Vibrational relaxation behind incident shock waves in pure nitrogen, using end wall pressure measurements

Journal ArticleDOI
TL;DR: In this article, the formation of NO behind incident shock waves in dilute O3-N2 mixtures was studied over the temperature range 3100-6400°K with initial pressures of 2-25 torr.
Abstract: The kinetics of the reaction O+N2+3.3 eV→NO+N were investigated under conditions where the vibrational temperature of the nitrogen was less than the translational temperature. The formation of NO behind incident shock waves in dilute O3–N2 mixtures was studied over the temperature range 3100–6400°K with initial pressures of 2–25 torr. In the shock front O3→O+O2 and the reaction of the O with N2 is then rate‐limiting, followed by the fast reaction N+O2→NO+O. The NO was monitored in emission at 5.3 μ and the initial slopes were compared to theoretical calculations which included vibrational relaxation processes. The radiation rose linearly from the shock front with no incubation in accord with the theoretical calculations employing only translational energy to determine the fraction of collisions whose energy was above the endothermicity of reaction.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the growth of infrared emission at 2.7 μ from water vapor formed during the shock-initiated combustion of dilute H2-O2-Ar mixtures.

Journal ArticleDOI
TL;DR: Transition probabilities of visible and near-IR neon lines, using gas-driven shock tube spectroscopy, were obtained in this paper, where the transition probabilities were shown as a function of the number of neon lines.
Abstract: Transition probabilities of visible and near-IR neon lines, using gas-driven shock tube spectroscopy

01 May 1970
TL;DR: Computer program calculates thermodynamic properties from basic spectroscopic data and the output is a complete thermodynamic and chemical description of the gas.
Abstract: Computer program calculates thermodynamic properties from basic spectroscopic data. Program capacity is a mixture of 100 different species composed of ten different elements. The output is a complete thermodynamic and chemical description of the gas.

Journal ArticleDOI
TL;DR: Theoretical characteristics of the ignition phenomenon, wherein a homogeneous propellant is exposed to stagnant gas after a shock reflection, derived by a combination of numerical and approximate techniques, are discussed in this paper.
Abstract: Theoretical characteristics of the ignition phenomenon, wherein a homogeneous propellant is exposed to stagnant gas after a shock reflection, derived by a combination of numerical and approximate techniques, are discussed. The one-dimensional model considered variable gas density, simultaneous diffusion and chemical reaction, self-determining (feedback) conditions at the solid-gas interface, and various solid and gas phase compositions. The descriptive equations were integrable over the whole time to achieve steady combustion of the solid, giving a complete spectrum of ignition results. In particular, approaching the steady state, a predictable, inverse square dependence on external oxidizer mole fraction was found for the ignition delay. This was true with large external oxidizer mole fractions, even with feedback operative, and resulted n a twin reaction zone structure which disappeared at low oxidizer mole fractious. This effect was found for a wide range of gas phase stoichiometry and solid composition. Further data are presented for a wide range of pyrolysis rates of the solid.

Journal ArticleDOI
TL;DR: In this article, the hydrogen-oxygen induction period kinetics behind shock waves, monitoring OH concentration by UV line absorption method is described. But the method is not suitable for the case of large-scale events.

Journal ArticleDOI
TL;DR: In this paper, the authors measured water vapor emission between 4.7 and 10 μ from 1300 to 3600°K using a shock tube to heat the gas and an optical system calibrated by a black body to measure the radiation.
Abstract: Water vapor emission between 4.7 and 10 μ from 1300 to 3600°K has been measured using a shock tube to heat the gas and an optical system calibrated by a black body to measure the radiation. The optically thin data are interpreted in terms of v2-band emission with some contribution, at the higher temperatures, from the pure rotational band. Calculable concentrations of H2O were made behind incident shocks from the reactions of H2 and O2 highly diluted in argon. There is excellent agreement between data taken at the equilibrium and “partial equilibrium” states, thereby providing additional justification for the existence of the partial equilibrium state and Schott's method for calculating it. An integrated band intensity of 338 (+17 per cent - 7 per cent) ama-1 cm-2 at 2000°K is deduced, in good agreement with earlier workers using different techniques. Above 2500°K the measured radiation is less than we calculate for our bandpass, assuming contributions from both the v2 and the rotational bands of H2O; possible reasons for this discrepancy are discussed.

Journal ArticleDOI
TL;DR: In this article, the role of the ratio of average molecular weight on the formation of the contact surface of a shock tube with a bursting diaphragm is explored. But the results are correlated with a theory that supposes turbulent mixing due to a Rayleigh Taylor instability, and a criterion or L ratio is defined which predicts when the turbulent mixing is sufficient to destroy the hot gas sample of the pure test gas.
Abstract: In a shock tube, with a bursting diaphragm, the separation of the test gas from the driver gas at the contact surface does not always occur. In this paper helium‐argon test gas mixtures are used with a helium driver to explore the role of the ratio of average molecular weight on the formation of the contact surface. The results are correlated with a theory that supposes turbulent mixing due to a Rayleigh‐Taylor instability, and a criterion or L ratio is defined which predicts when the turbulent mixing is sufficient to destroy the hot gas sample of the pure test gas.

Journal ArticleDOI
TL;DR: In this article, total ionization times in shock-heated argon, krypton, neon, and xenon have been calculated, taking into account atom-atom collisions, electron-atom collision, and recombination.
Abstract: Total ionization times in shock‐heated argon, krypton, neon, and xenon have been calculated, taking into account atom–atom collisions, electron–atom collisions, and recombination. Excellent agreement is found with the experimental results obtained for argon, neon, and some experiments on xenon. The highly inconsistent results obtained by some investigators for xenon have probably been due to high impurity levels and inadequate testing times in the shock tube.

Journal ArticleDOI
TL;DR: The behavior of flush-mounted electrostatic probes has been investigated in a pressured-riven, arc-heated shock tube over a wide range of shock tube freestream conditions and probe bias voltage as mentioned in this paper.
Abstract: The behavior of flush-mounted electrostatic probes has been investigated in a pressuredriven, arc-heated shock tube over a wide range of shock tube freestream conditions and probe bias voltage. Measurements were made with large one-dimensional, flush electrostatic probes at initial shock tube pressures of 0.1 and 1.0 torr. Freestream electron densities ranged from 10 to almost 10 elec/cm. The flush electrostatic probes were biased at —3, — 15 and —90 v. The experimental results support predictions for which theories are available over the range of conditions corresponding to the case of sheath dimension small compared to the velocity boundary-layer thickness and frozen chemistry in the boundary layer. However, even at electron densities an order of magnitude below that for which the thinsheath assumption is valid, the deviation of the experimental data from theoretical predictions does not exceed the data scatter. The saturated ion current density collected by the probe was found to vary with the bias voltage raised to the one-half power.


Journal ArticleDOI
TL;DR: In this article, the effect of the cold boundary layer on kinetic parameters was studied behind reflected shocks in a single pulse shock tube, and it was shown that the lowering of the chemical conversion was proportional to the surface-to-volume ratio in the test section.
Abstract: The effect of the cold boundary layer on kinetic parameters was studied behind reflected shocks in a single pulse shock tube. By inserting hollow cylinders into the test section, parallel to the tube walls, the surface relative to the volume was increased, and the lowering of the chemical conversion was determined as a function of the surface per unit volume. The test reaction studied was the unimolecular decomposition of perfluorocyclobutane (C4F8→2C2F4). It was shown that the lowering of the chemical conversion was proportional to the surface‐to‐volume ratio in the test section. A hypothetical cold layer δc in which no conversion occurred was found to be around 0.2 mm. It was concluded that in a shock tube of ∼ 2‐in. i.d., at an initial pressure of p1 ≥ 100 torr the cold boundary layer has very little effect on kinetic parameters obtained in a single‐pulse shock tube. At lower pressures and in smaller diameters shock tubes these effects should be considered when interpreting kinetics results.

Journal ArticleDOI
TL;DR: In this paper, a higher order theory is developed to treat the refraction of the incident oblique shock wave by irrotational or rotational disturbances of arbitrary amplitude provided the flow is supersonic behind the shock.
Abstract: : The general problem studied is the propagation of an oblique shock wave through a two-dimensional, steady, non-uniform oncoming flow. A higher order theory is developed to treat the refraction of the incident oblique shock wave by irrotational or rotational disturbances of arbitrary amplitude provided the flow is supersonic behind the shock. A unique feature of the analysis is the formulation of the flow equations on the downstream side of the shock wave. Analytical and numerical solutions to the basic shock refraction relation are presented for a broad range of flows in which the principal interaction occurs with disturbances generated upstream of the shock. These solutions include the passage of a weak oblique shock wave through: a supersonic shear layer, a converging or diverging flow, a pure pressure disturbance, Prandtl-Meyer expansions of the same and opposite family, an isentropic non-simple wave region, and a constant pressure rotational flow. The comparison between analytic and numerical results is very satisfactory. (Author)


Journal ArticleDOI
TL;DR: In this paper, a chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave in a shock tube is examined on a quantitative basis.
Abstract: A chemical kinetic model describing photochemical reactions that are likely to be important in "cold" argon ahead of a strong shock wave in a shock tube is examined on a quantitative basis. The model includes the propagation of resonance radiation far from the shock front in the wings of the resonance absorption line, imprisonment of the absorbed resonance radiation, subsequent photoionization of excited atoms, photoionization of ground state argon, and certain recombination and de-excitation processes. Specific consideration is given to shock tube geometry, the finite extent of the equilibrium region and the (experimentally) known shock tube wall reflectivity. Theoretical predictions of excited atom and argon ion concentrations in the precursor region are presented for typical shock tube operating conditions. The regimes favorable to the production of argon ions by photoionization of ground state argon and by photoionizati on of photoexcited argon, respectively, are delineated.