Showing papers on "Shock tube published in 1977"
TL;DR: In this article, the authors measured hydrogen-air induction times near the second explosion limit and matched these experimental results with numerically predicted induction times, the rate coefficient for the reaction H + O2 + M = HO2+M was evaluated as k-sub 4,N2 = 3.3 (plus or minus.6) x 10 to the 15 cm to the 6th/sq mole/s.
121 citations
01 Oct 1977
TL;DR: In this paper, the sensitization of stoichiometric hydrogen-air ignition by NO, NO2 and a mixture of NO and NO2 was investigated behind reflected shock waves in a shock tube.
Abstract: The sensitization of stoichiometric hydrogen-air ignition by NO, NO2 and a mixture of NO and NO2 was investigated behind reflected shock waves in a shock tube. Induction times were measured in pressure range 0.27 to 2.0 atm, temperature range 800 to 1500 K, and for NO or NO2 mole percent between 0.0 and 4.5. Addition of both NO and NO2 reduced the measured induction times. The experimental data are interpreted in terms of H2-O2-NO(x) oxidation reaction mechanisms. The influence of NO(x) upon a supersonic combustion ramjet combustor test, conducted in an arc-heated facility, is assessed.
94 citations
TL;DR: In this article, a method and apparatus for recovering oil from an oil bearing soil by means of an electrohydraulic shock wave generated in a liquid by capacitor electrical discharge means is described.
Abstract: A method and apparatus are provided for recovering oil from an oil bearing soil by means of an electrohydraulic shock wave generated in a liquid by capacitor electrical discharge means.
54 citations
TL;DR: In this article, the decomposition of nitrous oxide has been studied in the temperature range 1815-3365K using a shock tube technique using infrared emission from the 5.3μm vibration-rotation band of NO and from the 4.5 μm vibration rotation band of N2O.
Abstract: The decomposition of nitrous oxide has been studied in the temperature range 1815-3365K using a shock tube technique. Principal results of this study were the determination of the rate constants for the reactions and The experiments were conducted behind incident shock waves in mixtures of N2O and various diluent gases (Ar, Kr, N2, O2). Infrared emission from the 5.3 μm vibration-rotation band of NO and from the 4.5 μm vibration-rotation band of N2O was used to monitor the concentration-time profiles of NO and N2O. A computer simulation of the experiments was used to infer k1 and k2, with the following best-fit results: and for M = Ar, Kr, N2
43 citations
TL;DR: In this article, the pyrolysis of acetylene was investigated behind reflected shock waves in a single-pulse shock tube over the temperature range from 1000 to 1670 K. The major products were 1-buten-3-yne, 1,3-butadiyne, and hydrogen.
Abstract: The pyrolysis of acetylene was investigated behind the reflected shock waves in a single-pulse shock tube over the temperature range from 1000 to 1670 K. The major products were 1-buten-3-yne, 1,3-butadiyne, and hydrogen. The main primary C4 product, however, changes from 1-buten-3-yne to 1,3-butadiyne with the increase of temperature. At the lower temperatures the formation of 1-buten-3-yne dominates the pyrolysis of acetylene. The rate of 1-buten-3-yne formation is second order with respect to acetylene concentration, and its second-order rate constant is expressed as follows: k(cm^3 mol^-1s^-1)=10^14.39±0.26exp((-46400±1400)/RT) The isotopic distribution of 1-buten-3-yne in the pyrolysis of the equimolar C2H2 and C2D2 mixture, proved that the pyrolysis proceeds via a free-radical mechanism. A free-radical chain mechanism initiated by the bimolecular reaction of acetylene, 2C2H2→C4H3+H, was proposed.
40 citations
TL;DR: In this article, the authors derived a more precise value for the krypton-krypton collision excitation crosssection, S*Kr-Kr −Kr = 1.2 × 10−19 cm2/eV with or without the addition of hydrogen.
Abstract: At shock Mach numbers in pure krypton, at initial pressures p0 ~ 5 Torr, and final electron number densities ne ~ 1017 cm−3, the translational shock front in a 10 cm × 18 cm hypervelocity shock tube develops sinusoidal instabilities which affect the entire shock structure including the ionization relaxation region, the electron-cascade front and the final quasi-equilibrium state. By adding a small amount of hydrogen (~0.5% of the initial pressure), the entire flow is stabilized. However, the relaxation length for ionization is drastically reduced to about one half of its pure-gas value. Unlike argon the stability appears to diminish with the addition of hydrogen beyond about 0.5%. Using the familiar two-step collisional model coupled with radiation-energy loss and the appropriate chemical reactions, it was possible from dual-wavelength interferometric measurements to deduce a more precise value for the krypton–krypton collision excitation cross-section, S*Kr–Kr = 1.2 × 10−19 cm2/eV, with or without the pr...
30 citations
24 citations
TL;DR: The line width of the Ca(II) 3968 A and Na(I) 5890 A resonance lines broadened by electric microfields in a plasma were measured using a pressure-driven shock tube as the light source as discussed by the authors.
Abstract: Line widths of the Ca(II) 3968 A and Na(I) 5890 A resonance lines broadened by electric microfields in a plasma were measured. A pressure-driven shock tube was used as the light source. Radiation from the equilibrium region behind the reflected shock wave was studied using a rapid scanning Fabry-Perot interferometer. Electron and argon atom densities of about 8 x 10 to the 16th and 1 x 10 to the 19th/cu cm, respectively, were achieved at the relatively low temperature of around 7500 K by vaporizing a cesium powder that had been added to the shock tube as a solid aerosol in argon gas. The measured line widths were predominantly Stark broadened by the electrons and ions in the plasma, although Doppler, van der Waals, instrument function and optical depth effects had to be taken into account.
23 citations
TL;DR: In this paper, it was shown that O2 is slightly more efficient at deactivating the bending mode of CO2 than is N2, and the rate constant for its deactivation by air at 210 K has been estimated.
23 citations
TL;DR: In this article, the thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods, and it is possible to obtain information on the rate of the reaction 2NO2 antisymmetric-NO3 + NO.
Abstract: The thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 antisymmetric-NO3 + NO. The results on the reaction, NO2 + SO2 NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low-temperature data and provides a modification of the rate-constant expression that is applicable over a wide temperature range.
22 citations
TL;DR: In this article, the exchange reaction between hydrogen and deuterium was studied behind reflected shocks in a single pulse shock tube, where a vacuum uv monochromator and a Lyman-α radiation source were attached to the end block of the driven section in order to determine the hydrogen atom profile during the hot phase.
Abstract: The exchange reaction between hydrogen and deuterium was studied behind reflected shocks in a single pulse shock tube. A vacuum uv monochromator and a Lyman‐α radiation source were attached to the end block of the driven section in order to determine the hydrogen atom profile during the hot phase. These atoms are the result of impurities which are present in the shock tube. Two calibration attempts of the It/I0 vs [H]t around 1250 °K, using the decomposition scheme of propane and the postexplosion conditions in H2/O2/Ar mixtures, were unsuccessful. A calibration method which utilizes an integrated absorption profile is described. A two parameter calibration function (modified Beer–Lambert law) was derived: It/I0=exp(−α[H]βt), where α=2.92×107 and β=0.73 in units of mole‐cm. For each test, a sample was withdrawn from the tube and was analyzed mass spectrometrically for postshock distribution of product and reactants. In addition, the absorption profile at 1215.7 A was recorded and the extent of HD produced...
TL;DR: In this article, the radiative energy loss from an argon plasma in a shock tube has been investigated, with emphasis on the role of reabsorption, and electron densities reached values of 1.5*1024 electrons m-3 behind the primary shock, and 2.5 *1025 electrons m −3 after shock reflection.
Abstract: The radiative energy loss from an argon plasma in a shock tube has been investigated, with emphasis on the role of reabsorption. Electron densities reached values of 1.5*1024 electrons m-3 behind the primary shock, and 2.5*1025 electrons m-3 after shock reflection. For the primary shock, emissivity effects outweighed reabsorption, whereas the axial gradients of gas properties caused by radiative cooling, which were observed by other investigators in experiments at lower electron densities, increased in these experiments. However, for the reflected shock region, the relative influence of reabsorption increased sufficiently to reduce the cooling rate due to radiation.
TL;DR: In this article, the rate of dissociation of Br2 in the presence of Ar and Br2 has been investigated using three independent experimental techniques in the same shock tube: molecular absorption spectroscopy (AS), two-body emission spectrumopy (ES), and laser schlieren technique (LS), and present results yield recombination rate constants in good agreement with each other and with earlier high temperature flash photolysis data.
Abstract: The rate of dissocation of Br2 in the presence of Ar and Br2 has been investigated using three independent experimental techniques in the same shock tube: molecular absorption spectroscopy (AS), two‐body emission spectroscopy (ES), and laser schlieren technique (LS). Present results yield recombination rate constants in good agreement with each other and with earlier high temperature flash photolysis data. The temperature range over which dissociation was studied was extended from 1200 to 3000 °K. Recombination rate constants can be summarized in terms of the following equations: log10krAr(LS) =8.251(±0.002)−1.36(±0.29)log10(T/2300) or log10krAr(LS) =8.378(±0.001)−1.05(±0.30) log10(T/2300). The difference between these two equations arose because in the first equation RBr=RBr2 was assumed, while in the second RBr=RKr was used. Here Rx is the Gladstone–Dale constant of X. These equations are valid between 1600 and 3000°K. The analogous equations for krBr2 are: log10kBr2=8.718(±0.001)−2.35(±0.41)log10(T/190...
TL;DR: In this paper, the modified two stream flute mode, driven unstable by the density and temperature gradients, can heat the ions to about 50 times their upstream temperature, however, the electrons are heated mainly by the non-flute mode and their temperature can be increased by a factor of 1·5 or more.
Abstract: Ion and electron heating in the earth's bow shock region is studied in terms of the modified two stream instability by treating the electron's response to be electromagnetic and that of ions to be electrostatic. The modified two stream flute mode, driven unstable by the density and temperature gradients, can heat the ions to about 50 times their upstream temperature. However, the electrons are heated mainly by the non-flute mode and their temperature can be increased by a factor of 1·5 or more. Consequently the ions will be hotter than the electrons downstream of the shock, as observed by satellites.
TL;DR: In this article, an extension of Griffith's work on shock/thermal layer interactions has been made, where flow properties in a transition region between the foot of the shock and the thermal layer are obtained; temperatures are reported.
Abstract: Some extensions of Griffith’s work on shock/thermal layer interactions have been made. In particular, flow properties in a transition region between the foot of the shock and the thermal layer may be obtained; temperatures are reported.
TL;DR: In this paper, a model for calculating laminar-turbulent transition in the boundary layer of flows in chemical shock tubes is proposed, where the time to turbulent transition may be treated as the time required by the shocked gas to move over one shock-tube diameter.
Abstract: A model is proposed for calculating laminar-turbulent transition in the boundary layer of flows in chemical shock tubes. It is shown that the time to turbulent transition may be treated as the time required by the shocked gas to move over one shock-tube diameter. The model is shown to provide a means of predicting the turbulent transition time in any shock tube experiment, provided the condition of limiting flow is met. Knowing the transition time, it becomes possible to obtain the density and temperature profiles and, hence, to determine precisely the effect of shock tube boundary layers on the measurement of chemical rate constants.
TL;DR: In this article, an observing method of shock wave by using an electric discharge has been tried, which is based on the fact that a radiation intensity of electric discharge depends on gas densities, and the location of the shock wave can be easily found by taking a photograph of this discharge column.
Abstract: Theme O PTICAL systems such as schlieren systems, MachZehnder interferometers, and shadowgraphs have been used as typical methods to observe shock waves around models. However, any shock shape cannot necessarily be observed by these optical systems. For instance, it is difficult to measure a cross-section of a shock wave around a model, especially that around a winged body as shown in Fig. 1. In this case the shock shape in the shaded region (dotted line) cannot be observed by any optical method, because a part of the optical axes is intercepted by the body. In this paper, an observing method of shock waves by using an electric discharge has been tried. The principle of the method is based on the fact that a radiation intensity of an electric discharge depends on gas densities. When an electric discharge is generated across a shock wave, the radiation intensity in the shock layer is different from that in the freestream according to the difference of each density, consequently the location of the shock wave can be easily found by taking a photograph of this discharge column. Since the location of the electrodes may be chosen arbitrarily and the discharge column can be observed from any direction, it will be expected to be able to observe cross-sectional shock shapes or the shock wave in a shaded region as stated above. W I N G E D BODY
01 Jan 1977
TL;DR: In this article, the authors used reflected wave end-on method to study the induction zone of shock-initiated explosions of carbon disulfide-oxygen-argon mixtures.
Abstract: The induction zone of shock-initiated explosions of carbon disulfide-oxygen-argon mixtures was studied using the reflected wave end-on method. Profiles of chemiluminescence at 490 nm, attributed to SO2o, and infrared emission at 5 μm, attributed to CS2 and CO, were analyzed to deterrine the characteristic branched-chain growth rates and ignition delay times over the temperature range 1400–2100 K for CS2:O2 ratios varying from 1:9 to 3:10 with various dilutions in argon. Computer modelling in terms of a conventional mechanisms for the CS2−O2 reaction was able to account for the ignition delay times under a variety of assumptions about the high temperature rate constants, but no adjustments of the mechanism or the rate constants were found that were capable of giving satisfactorily correct models of the qualitative forms of the visible emission profiles or the mixture dependence of the growth rates.
01 Jan 1977
TL;DR: In this article, a method to determine the onset of vapor condensation by homogeneous nucleation in the unsteady flow in a centered expansion wave generated in a shock tube is described.
Abstract: : A method to determine the onset of vapor condensation by homogeneous nucleation in the unsteady flow in a centered expansion wave generated in a shock tube is described. The test gas, consisting of an inert carrier gas and a vapor, is taken to be an inviscid perfect gas, and the flow is assumed to remain isentropic up to the point of onset of condensation. The latter assumption is valid in experiments where onset is made to occur at the tail of the expansion. Under these conditions the condensation rate is found by combining gasdynamics and the kinetics of nucleation and droplet growth. The method discussed is not limited to a particular choice of the kinetic equations. Finally, we present as an illustration, a procedure with which the nucleation rate in an experiment may be deduced and compared with theory. (Author)
01 Jan 1977
TL;DR: In this paper, a centered expansion fan was used to study condensation of H2O and D2O vapors in an excess of the carrier gas argon, with simultaneous pressure and light scattering measurements.
Abstract: : Despite gasdynamic non-idealities in the flow produced in a shock tube, pressure measurements at three different locations in the driver section of the shock tube revealed that the expansion wave generated in relatively weak expansions could be viewed effectively as a simple centered expansion fan after an empirical shift of the actual origin of the expansion wave to a 'virtual' origin. The resulting centered expansion fan was used to study at two locations the condensation of H2O and D2O vapors in an excess of the carrier gas argon, with simultaneous pressure and light scattering measurements. The isentropic flow within the centered expansion fan was found to be preserved up to the point of the detectable onset of condensation by tailoring the onset conditions to occur at the tail of the expansion fan, thus rendering a simple analysis of the experiments possible. The onset conditions of H2O vapor were found to be in agreement with previous findings in supersonic nozzles and shock tubes, and they were well predicted by the so-called classical theory of homogeneous nucleation. The condensation of D2O vapor was found to exhibit similar trends as those of H2O vapor condensation despite the slight differences in physical properties between them due to isotopy. (Author)
TL;DR: In this article, the breakdown delay in two extreme cases of high and low power deposited in the gas, in terms of four time constants, i.e., relaxation time, power time, the time required for the electric power to raise the pressure level of the gas to ambient, theasperity time, and the sheath time, being the time of a sound wave to traverse a roughness element or asperity of the electrode surface.
Abstract: When a steep-fronted voltage step is applied to the electrodes in a preionized gas, the high electric field in the cathode sheath, together with current continuity across the sheath causes preferential heating and pressure increase of the gas in the sheath region. The situation is somewhat analogous to that in a shock tube at the instant of diaphragm rupture. However, owing to the current, the cathode sheath goes unstable, forming filaments of hot gas from the sheath. Expressions are derived for the breakdown delay in the two extreme cases of high and low power deposited in the gas, in terms of four time constants, i.e. the relaxation time, the 'power time', being the time required for the electric power to raise the pressure level of the gas to ambient, the 'asperity time', i.e. the time taken by a sound wave to traverse a roughness element or asperity of the electrode surface, and the 'sheath time', being the time of the wave's traverse of the sheath thickness. It is shown that the theory is in substant...
TL;DR: Stark widths and shifts of nine neutral fluorine spectral lines emitted by the shock tube plasma have been measured and compared with both: previous experimental results [1] and theory [4] as discussed by the authors.
01 Oct 1977
Abstract: : A 180 sector of the first stage stationary inlet nozzle of the AiResearch TFE-731-2 engine was instrumented with thin-film heat-transfer gages and experiments were performed to obtain detailed heat-transfer rate distributions. It is shown that the experimental apparatus can potentially be used to study total-pressure losses in cascades. The experimental apparatus consists of a helium-driven shock tube as a short-duration source of high-temperature high-pressure gas, driving a nozzle test-section device mounted near the exit of a primary shock-tunnel receiver tank. The nozzle test-section device consists of a forward transition section with a circular opening facing the supersonic primary nozzle flow and with the external shape of a frustum of a cone. Internal contouring is provided to transform the circular-section subsonic intake flow into one filling approximately a 180 annular segment having a geometry approximating that of the entrance to the turbine stator stage in a turbojet. Detailed measurements of static pressure in the test section and heat-transfer rate on the stator sector have been obtained and are reported herein. (Author)
01 Jun 1977
TL;DR: In this article, the attenuation of a set of perforated plates passing through a 4-inch (10.2 cm) tube over a range of peak shock overpressures from 200 psi (1379 kPa) down to 48 psi (331 kPa).
Abstract: : Results are presented for a set of experiments designed to determine the attenuation of shock waves passing through perforated plates as a function of peak overpressure and hole size for a given percentage of plate area vented. The venting hole size was varied from 1/8 inch (0.32 cm) to 2-13/16 inches (7.14 cm) as the vented area was varied from 5-50 percent open. The perforated plates were exposed to shock waves in a 4-inch (10.2 cm) shock tube over a range of peak shock overpressures from 200 psi (1379 kPa) down to 48 psi (331 kPa).
30 Nov 1977
TL;DR: In this paper, the effects of impurities such as hydrogen, water vapour and sodium chloride on the stability and structure of ionizing-argon and krypton flows were investigated by using a dual-wavelength Mach-Zehnder interferometer in conjunction with the UTIAS 10cm x 18cm (4in x 7in) Hypervelocity Shock Tube.
Abstract: : The effects of impurities - hydrogen, water vapour and sodium chloride - on shock wave stability and structure in ionizing-argon and krypton flows were investigated by using a dual-wavelength Mach-Zehnder interferometer in conjunction with the UTIAS 10cm x 18cm (4in x 7in) Hypervelocity Shock Tube. At shock Mach number of about 15, when pure argon or krypton is used as a test gas, the resulting translational shock front develops sinusoidal oscillations. The subsequent ionization relaxation region, the electron-cascade front and the quasi-equilibrium state also exhibit unstable characteristics. The addition of small amounts of hydrogen ( or = 0.5% by pressure) to the test gas stabilizes the entire flow and at the same time drastically shortens the relaxation length to about 1/3 of the original value in argon and 2/3 in krypton. The addition of about 1% of water vapour (by pressure) to the argon test gas also stabilizes the flow and shortens the relaxation region. A thin coating of dissolved sodium chloride in water on the shock tube wall, which on evacuation leaves a rough surface of crystals, however, does not seem to have any effect on the flow.
TL;DR: In this article, a new form for the general solution to the thin-shock-layer equations for the flow over a nearly plane delta wing is given, and the solution described conjecturally by Hayes & Probstein is realized numerically.
Abstract: A new form is given for the general solution to the thin-shock-layer equations for the flow over a nearly plane delta wing. Using this, the solution described conjecturally by Hayes & Probstein for symmetrical flow with attached shock waves over a plane delta wing is realized numerically. The flow construction devised for this purpose is applied also to yawed flows. The solutions obtained are found to agree moderately well with the results of numerical calculations from the full equations, but contain a number of anomalous features characteristic of the thin-shock-layer approximation.
TL;DR: In this article, the authors considered the non-instantaneous opening of the diaphragm and proposed a multistage model to model the formation process of a plane shock wave.
Abstract: Introduction A the perturbational phenomena of the flow generated by the incident shock wave in a shock tube, one of the most important comes from the noninstantaneous opening of the diaphragm. The flow has a three-dimensional behavior in the first instants of the rupture and compression waves continually arise next to the diaphragm during the opening, generate first a shock wave, accelerate and strengthen this wave. Many experiments, both old and new, have shown the importance of these effects. The formation process of a plane shock wave is confined in a small length of the tube, but the acceleration process may require a large tube length, depending on initial conditions, diaphragm material and shape, and the tube itself. White's model is an approximation of the formation process; in the x,t diagram, compression waves are assumed to coalesce in a single point where the shock possesses its final and constant value, but the acceleration process is not taken into account. More recently, the "multistage" model may be considered as an improvement of White's model but it is still a discontinuous model. In the present model, the flow regime is related to the opening process itself. Boundary-layer effects are neglected, although it would not be too difficult to include them. In the same way, the formation phase itself will not be taken into account, but a numerical method of determination of the flow variables is developed in order to describe the acceleration phase.