Shock-tube

A general limitation of the relaxation teclmiques with small perturbations from equilibrium discussed in the previous section arises from the restriction to systems starting at or near equilibrium under the conditions used. This limitation is overcome by teclmiques with large perturbations. The most important representative of this class of relaxation techniques in gas-phase kinetics is the shock-tube method, which achieves J-jumps of some 1000 K (accompanied by corresponding P-jumps) [30, and 53]. Shock hibes are particularly... 

Figure B2.5.5. Schematic representation of a shock-tube apparatus. The diapliragm d separates the high-...

Figure B2.5.6. Temperature as a fiinction of time in a shock-tube experiment. The first r-jump results from the incoming shock wave. The second is caused by the reflection of the shock wave at the wall of the tube. The rise time 8 t typically is less than 1 ps, whereas the time delay between the incoming and reflected shock wave is on tlie order of several hundred microseconds. Adapted from [110].

A classic shock-tube study concerned the high-temperature recombination rate and equilibrium for methyl radical recombination [M, Ml- Methyl radicals were first produced in a fast decomposition of diazomethane at high temperatures (T > 1000 K)... 

In a more recent example, a shock-tube experiment was used to study the themial decomposition of methylamine between 1500 K and 2000 K [61, 62] ... 

The pyrolysis of CR NH (<1 mbar) was perfomied at 1.3 atm in Ar, spectroscopically monitoring the concentration of NH2 radicals behind the reflected shock wave as a fiinction of time. The interesting aspect of this experiment was the combination of a shock-tube experiment with the particularly sensitive detection of the NH2 radicals by frequency-modulated, laser-absorption spectroscopy [ ]. Compared with conventional narrow-bandwidth laser-absorption detection the signal-to-noise ratio could be increased by a factor of 20, with correspondingly more accurate values for the rate constant k T). 

Tree J 1975 Shock wave studies of elementary chemical processes Modern Deveiopments in Shock Tube Research ed G Kamimoto (Japan Shock Tube Research Society) pp 29-54... 

Votsmeier M, Song S, Davidson D F and Hanson R K 1999 Shock tube study of monomethylamine thermal decomposition and NH2 high temperature absorption coefficients int. J. Chem. Kinetics 31 323-30... 

Shirakawa techmqi Shirlan Shirley Non-Lint AnalyZ Shi take mushroom Shock absorbers Shock absorption Shocking Shockley defects Shock treatment Shock tubes Shock waves Shoe components Shoe products Shoes... 

Chemical Properties. The kinetics of decomposition of OF2 by pyrolysis in a shock tube are different, as a result of surface effects, from those obtained by conventional decomposition studies. Dry OF2 is stable up to 250°C (22). 

S. C. Lin, E. L. Reslei, and A. R. Kantiowitz,/. Appl Phjs. 26(1), 83—95 (fan. 1955) H. E. VetscReR, Approach to Equilibrium behind Strong Shock Waves in Argon, Pli.D. dissertation, Cornell University, Ithaca, N.Y., 1955 R. M. Patrick, Magnetohjdrodynamics of a Compressible Fluid, Pli.D. dissertation, Cornell University, Ithaca, N.Y., 1956 R. J. Rosa, EngineeringMagnetohjdrodynamics, Ph.D. dissertation, Cornell University, Ithaca, N.Y., 1956 J. Jukes, Ionic Heat Transfer to the Walls of a Shock Tube, Ph.D. dissertation, Cornell University, Ithaca, N.Y., (1956). 

Oppenheim, A. K., J. Kurylo, L. M. Cohen, and M. M. Kamel. 1977. Blast waves generated by exploding clouds. Proc. 11th Int. Symp. on Shock Tubes and Waves. pp. 465-473. Seattle. 

Initial shock-wave overpressure can be determined from a one-dimensional technique. It consists of using conservation equations for discontinuities through the shock and isentropic flow equations through the rarefaction waves, then matching pressure and flow velocity at the contact surface. This procedure is outlined in Liepmatm and Roshko (1967) for the case of a bursting membrane contained in a shock tube. From this analysis, the initial overpressure at the shock front can be calculated with Eq. (6.3.22). This pressure is not only coupled to the pressure in the sphere, but is also related to the speed of sound and the ratio of specific heats. 

Fig. 5. Gas-phase ignition of propellant samples in shock tube (P8).

FIGURE 5.1 Arrhenius behavior over a large temperature range. (Data from Monat, J. P., Hanson, R. K., and Kruger, C. H., Shock tube determination of the rate coefficient for the reaction N2 + O- NO + N, Seventeenth Symposium (International) on Combustion, Gerard Faeth, Ed., The Combustion Institute, Pittsburgh, 1979, pp. 543-552.)... 

A. G. Gaydon and 1. R. Hurle, The Shock Tube in High-Temperature Chemical Physics, Reinhold, New York, 1963. 

After the flue gas leaves the combustion chamber, most furnace designs extract further heat from the flue gas in horizontal banks of tubes in a convection section, before the flue gas is vented to the atmosphere. The temperature of the flue gases at the exit of the radiant section is usually in the range 700 to 900°C. The first few rows of tubes at the exit of the radiant section are plain tubes, known as shock tubes or shield tubes. These tubes need to be robust enough to be able to withstand high temperatures and receive significant radiant heat from the radiant section. Heat transfer to the shock tubes is both by radiation and by convection. After the shock tubes, the hot flue gases flow across banks of tubes that usually have extended surfaces to increase the rate of heat transfer to the flue gas. The heat transferred in the radiant section will usually be between 50 and 70% of the total heat transferred. 

Our data can be used to estimate the effective temperatures reached in each site through comparative rate thermometry, a technique developed for similar use in shock tube chemistry (32). Using the sonochemical kinetic data in combination with the activation parameters recently determined by high temperature gas phase laser pyrolysis (33), the effective temperature of each site can then be calculated (8),(34) the gas phase reaction zone effective temperature is 5200 650°K, and the liquid phase effective temperature is 1900°K. Using a simple thermal conduction model, the liquid reaction zone is estimated to be 200 nm thick and to have a lifetime of less than 2 usee, as shown in Figure 3. 

MW Slack, AR Grillo. Proc Int Symp Shock Tubes Waves 11 408, 1978. 

Wagner, H. Gg. Gaseous Detonations and the Structure of a Detonation Zone (in Fundamental Data obtained from Shock Tube Experiments, Editor Ferri, A.). Pergamon Press, Oxford 1961... 

Basic Breakup Modes. Starting from Lenard s investigation of large free-falling drops in still air,12671 drop/droplet breakup has been a subject of extensive theoretical and experimental studies[268] 12851 for a century. Various experimental methods have been developed and used to study droplet breakup, including free fall in towers and stairwells, suspension in vertical wind tunnels keeping droplets stationary, and in shock tubes with supersonic velocities, etc. These theoretical and experimental studies revealed that droplet breakup under the action of aerodynamic forces may occur in various modes, depending on the flow pattern around the droplet, and the physical properties of the gas and liquid involved, i.e., density, viscosity, and interfacial tension. 

Because of its high thermal stability compared to that of other hydrides, water does not decompose extensively below 2000 °K. Thus, at one atmosphere and 2500 °K it is only dissociated to the extent of 9 %. Accordingly, it is impossible to study the homogeneous decomposition by classical methods. It is only with the shock tube technique that the rates of pyrolysis of water and heavy water have been measured. 

The overall stoichiometric equation for this decomposition leading to equilibrium depends on the temperature. A considerable amount of the final products are H, OH, and O. Bauer et al.3 were the first to report an investigation of the water dissociation by the shock-tube method. The temperature range for this study was 2400-3200 °K. They followed the reaction by measuring the uv absorption of the hydroxyl radical produced during the decomposition. The apparent activation energy for the parameter (1/ [H20])(d [OH]/df) of about 50 kcal.mole-1 seemed to indicate that the reaction... 

The gas-phase reaction has been studied using static reaction systems12-13, flow reactors10, u> 14,15 and, more recently, using the shock-tube technique16,17. The decomposition was followed in static experiments both measuring the... 

Although the concentrations of H202 in the shock-tube experiments were much... 

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

Shock tube experiments by Jacobs27 have shown that it is essential to purify the ammonia and the diluent from oxygen or other oxidizing components, otherwise oxidation would seriously interfere with decomposition. Jacobs followed the decay of ammonia through its infrared emission at 3 n in the temperature range 2100-3000 °K. He argued that an assumed reaction order of in ammonia and of i in the inert gas would best fit the observed concentration-time records, i.e. 

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