Throwing of fire-extinguishing powder jets from barrels

Time variations of current values of the velocity and propagation distance of the front of a gas-powder jet are studied as functions of the ratio of masses of the powder charge and the ejected fire-extinguishing composition. Three mechanisms of propagation of a pulsed gas-powder jet are established. An optimum range of mass ratios is obtained that provides for maximum values of the propagation distance of the gas-powder jet for barrels of various calibers and lengths. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 106–110, January–February, 1998.     

Rheological properties of liquid-crystalline solutions of poly(p-phenylene terephthalamide) and behavior of the jet in spinning through an air space

LC solutions of PPTA behave like liquids with a power law of flow and n =0.65–0.78 for flow through the channels of standard spinnerets with small diameters and q =0.88–0.95 for longitudinal flow in jets. Spinneret expansion of a freely falling jet in channels with small diameters is equal to 1.70–1.75 and is not a function of the shear rate on the wall. Spinneret expansion is preserved in conditions of repeated drawing of the jets in the air space until very small air spaces at 1.5–2.5 mm are used. In spinning PPTA fibres through an air space with a high jet draw ratio, only a small fraction of this drawing in the spinning bath is possible. Translated from Khimicheskie Volokna, No. 2, pp. 3–7, March–April, 1997.     

Modeling afterburning of high-speed turbulent jets

Heat transfer in a high-speed underexpanded turbulent jet is examined numerically. Profiles of the basic gas-dynamic and thermal parameters (velocity, temperature, and concentration of the species of the gas mixture) are determined. Afterburning of the high-speed jet in air is studied. The basic parameters affecting this process are established. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 3–9, March–April, 2006.     

Effect of the strain rate on the tensile strength of a copper shaped-charge jet

The data on the penetration depth of a rotating shaped-charge jet were used to estimate the strength of the material of a copper jet formed from a “low” conical linear with an apex angle of120° under the action of centrifugal forces. The estimates0.07–0.15 GPa obtained are close to the static yield point of deformed copper. The jet strength, which is estimated using the length of the fragments formed upon breakup of a rotation-free jet owing to the axial velocity gradient, attains1–1.5 GPa at a strain rate of ≌2·10⁴ sec⁻¹. Lavrent’ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 1, pp. 111–118, January–February, 1997.     

Guniting linings of oxygen converters in the course of melting without stopping the blow

Problems arising in guniting converter linings in the course of melting without stopping the oxygen blow are considered. Deposition of a mixture based on magnesite is conducted in an oxygen jet. As the powder particles move in the vessel, they are heated due to the heat of the converter and afterburning of carbon monoxide, which ensures their strong cohesion with the surface of the lining. The velocity and diameter of the gas-powder jet are calculated as a function of the concentration of the periclase powder, the distance from the tuyere nozzle, and the temperature of the magnesite particles heated in the vessel. An experimental installation is developed and experiments on guniting in the course of melting without interrupting the blow are conducted. It is established that the gunited coating is deposited on the lining only at the end of melting. The endurance of the coating is 1–4 heats. In guniting, the temperature of the metal increases by 20–70°C. The experiments showed the possibility in principle of guniting a converter lining in the course of melting without interrupting the blow. Translated from Ogneupory, No. 3, pp. 27–31, March, 1996.     

Disintegration of materials by reactive jets

Results of experiments on failure of materials by jets of a material that is reactive toward the disintegrating material are presented. A sodium low-pressure jet acted on water-saturated gypsum samples whose strength in compression was more than an order of magnitude higher than the stagnation pressure of the jet. The jet effectively penetrated into the material and disintegrated it at the expense of the thermal energy released as a result of the chemical reaction between the jet material and the disintegrating material. The specific energy expended in the disintegration of the material can be diminished by several orders of magnitude compared to the mechanical and hydrojet methods. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 106–108, July–August 1999.     

Elimination of jets formed by the interaction of detonation waves

We have considered the phenomenon of collision of detonation waves on the surfaces of aluminum and copper casings. It is shown that a cumulative jet is formed in the first case and a combination of cumulative and “three-shock” jets in the second. Experimentally checked methods of eliminating such jets are proposed. Institute of Experimental Physics, Sarov 607190. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 103–108, July–August, 1997.     

Wet spinning of acrylic microfibres

Polyacrylonitrile microfibres with a linear density of 0.02–0.10 tex can be manufactured by wet spinning into spinning baths with a low concentration of precipitant. When the jets of spinning solution come into contact with such a spinning bath, a concentration of precipitant lower than the threshold concentration where coagulation does not take place is established on the surface of the fibre for a short time (0.02–0.56 sec). The spun fibres have a liquid segment longer than the stressed part of the jet exposed to normal stresses. Fibres with a liquid segment can be drawn by 5–10 times, which allows fabricating microfibres with a linear density of 0.02–0.10 tex having a strength of 45–80 cN/tex and elongation of 15–20%. Fibres spun into baths with a low concentration of precipitant have high porosity, which could be attributed to formation of a liquid polymer phase in phase decomposition of the spinning solution. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 3, pp. 16–20, May–June, 2000     

Investigation of the structure of a diffusion hydrogen plume in a supersonic high-enthalpy air jet

The results of investigation of the plume structure in the case of diffusion combustion of hydrogen in a cocurrent supersonic high-enthalpy off-design air jet are presented. Based on the registration of radiation within the wavelength range of 260–350 nm across and along the flame, a three-dimensional tomographic reconstruction of the plume was obtained, which confirmed the interrelation between the gas-dynamic structure and combustion intensity. A possibility of existence of combustion regimes with periodically repeated cycles of complete extinction and subsequent ignition of hydrogen in accordance with the barrel-shaped structure of the off-design jet is established experimentally. The existence of local peripheral regions of combustion is noted, which can indicate the presence of vortex structures. In the three-dimensional representation (obtained under the assumption of axial symmetry of radiation), these vortex structures have the form of annular zones. In a real flow, helical structures are possibly formed at the plume periphery. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 3–5, September–October 1999.     

Researches in the gasdynamics of explosion and reacting systems

Conclusions The papers presented at the colloquium and the results from personal discussions indicate that the numerous applications of combustion and explosion processes in rocketry, industrial technology, and in safe handling of fuels during transportation have meant that researches on the gasdynamics of explosive phenomena are being vigorously pursued in the USA, France, Britain, Japan, and other industrially developed countries. Particular interest attaches to evidence presented at the colloquium on methods of calculating shock-wave parameters for large-scale explosions of gases and fuels, together with definition of the critical conditions for detonation propagation in chemically active media, as well as analysis of turbulent mixing and combustion in gases and heterogeneous systems. In particular, turbulent mixing, combustion, and detonation have major applications in laser engineering, and it has been shown, for instance, that separate excitation and turbulent mixing of nonequilibrium high-temperature gas flows can substantially improve the efficiency and optical characteristics of high-power gasdynamic laser systems. Efficient optical methods of diagnosis for combustion, detonation, and explosion processes have been developed in the USA and France, and these deserve attention and further study for use in experimental research. This applies particularly to laser Raman spectroscopy and laser holography. The next (Sixth) Colloquium will be held in August 1977 in Stockholm, and the President of the Organizing Committee for that colloquium was confirmed as Professor P. A. Person. Translated from Fizika Goreniya i Vzryva, Vol. 12, No. 3, pp. 472–481, May–June, 1976.     

Composite refractory protective coatings for carbon-graphite materials

Production examples are considered for improving the refractoriness of structural graphites and carbon-ceramic composite materials and constructions of them created on the basis of surface composite heat-resistant coatings based on molybdenum silicide and silicon carbide. The temperature limits for coating preparation and their operating capacity are determined. The structure of composite refractory coatings is studied by optical methods. The optimum limit for pyrolytic coatings is established. Translated from Novye Ogneupory, No. 10, pp. 45–50, October 2008.     

Size effect in laser-induced initiation of a pyrotechnical composition (ammonium perchlorate and ultrafine aluminum)

The energy thresholds and ignition delays of pressed samples of a stoichiometric pyrotechnical mixture of ammonium perchlorate and ultrafine aluminum are studied as functions of the diameter of the laser spot created by a millisecond laser pulse. A clearly expressed size effect is found. A characteristic size determining the boundary between the wide and narrow beams of the laser pulse applied is determined. The influence of optical properties of the examined composition on the behavior of the size dependences is discussed. The relation between the nature of the size effect and the laws of light scattering in the volume of powdered pyrotechnical mixtures is considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 77–82, November–December, 2008.     

On the ignition of a layer of combustible forest materials by light radiation

The ignition of a layer of combustible forest materials by luminous radiation was studied experimentally. The minimum radiant heat flux densities required to ignite combustible forest materials are determined for a neodymium-doped glass laser and a tungsten lamp. It is established that the heat flux, density increases with increase in the moisture content and density of the layer of combustible forest materials and decreases with increase in the diameter of the light spot, and the critical flux density is higher for the laser radiation than for the incandescent lamp. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 22–25, November–December 1999.     

Structural,Textural and Acid–Base Properties of Nano-Sized NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Spinel Catalysts

Abstract  

The effect of preparation methods on the textural, structural and acid–base properties of nano-sized nickel ferrite oxides was investigated. Several physicochemical methods are used for their characterization. Isopropanol, as a probe molecule, is used to determine acid–base properties. A correlation between textural, structural and acid–base properties of nanomaterials is established.     

Numerical simulation of the characteristics of turbulent Taylor vortex flow

Turbulent Taylor vortex flow, which is contained between a rotating inner cylinder and a coaxial fixed outer cylinder with fixed ends, is simulated by applying the development in Reynolds stress equations mold (RSM) of the micro-perturbation. This resulted from the truncation error between the numerical solution and exact solution of the Reynolds stress equations. Based on the numerical simulation results of the turbulent Taylor vortex flow, its characteristics such as the fluctuation of the flow field, the precipitous drop of azimuthal velocity, the jet flow of radial velocity, the periodicity of axial velocity, the wave periodicity of pressure distribution, the polarization of shear stress on the walls, and the turbulence intensity in the jet region, are discussed. Comparing the pilot results measured by previous methods, the relative error of the characteristics predicted by simulation is less than 30%. Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2006, 32(5), 617–622 [译自: 华东理工大学学报 (自然科学版)]     

Tests of a solid state laser pumped by radiation from a converging shock wave

A neodymium glass laser pumped optically by radiation from a strong converging shock wave in argon is tested. A condensed explosive charge with an inner cylindrical hollow is used to initiate the converging shock. A mathematical model confirms the feasibility of optical pumping by radiation from a converging shock with lasing. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 114–119, March–April 1999     

Platinum Assisted Vapor–Liquid–Solid Growth of Er–Si Nanowires and Their Optical Properties

We report the optical activation of erbium coated silicon nanowires (Er–SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl₄ and ErCl₄ as precursors. Pt as well as Au worked successfully as vapor–liquid–solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core–shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er³⁺ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er–SiNWs.     

Modern high-density oxide ceramics with a controlled microstructure. Part VI. Fabrication of light-transmitting oxide ceramic materials

Results obtained in fabrication of light-transmitting Y₂O₃-based ceramics with HfO₂ and ZrO₂ additives are described. The dependence of their sinterability and optical properties on the kind and amount of additives and some process parameters is established. Important physical and engineering properties of the best compositions of Glubor ceramics are compared with the properties of the imported Yttralox counterpart. For the beginning of the series see No. 1 of 1996, for the continuation see Nos. 2, 4–7, 9, 12 of 1996 and Nos. 1–3 and 7 of 1997. Translated from Ogenupory i Tekhnicheskaya Karemika, No. 8, pp. 2–11, August, 1997. (To be continued.)     

Effect of laser radiation and electric field on combustion of hydrocarbon-air mixtures

Publications on combustion of hydrocarbon-air mixtures under the action of a weak electric field and laser radiation are analyzed. A specific feature of the authors’ experimental study is a pulsed-periodic action of an electric field and focused laser radiation, which does not lead to electric discharge or optical breakdown. Numerous experiments reveal a noticeable effect of weak electric fields on combustion processes. Application of an electric field may result in expansion of the limits of flammability and combustion of fuel-air mixtures, changes (decrease or increase) in the burning rate, shifting of flame stabilization toward lean mixtures, reduction of the concentration of hazardous substances (for instance, NO _x and CO) in combustion products, etc. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 77–85, July–August, 2009.     

Improvement of Manufacturing Technology for Ultrastrong and High-Modulus Carbon Fibres

1. The quality of CF, their strength and modulus of elasticity in particular, can be increased by the following methods: reducing the porosity of the initial PAN fibres by selecting the optimum conditions for spinning, plasticization drawing, finishing, and drying; decreasing the nonuniformity of the fibre diameter due to suppression of deformation resonance during spinning by selecting the jet formation and hardening conditions; decreasing the fibril and crystallite size by reducing the precipitator and solvent concentration gradient in the precipitation zone (spinning into mild baths); creating optimum conditions for mesophase self-ordering of the material at 450–550° C during precarbonization; increasing the cohesive energy by increasing the density to 1.8–2.1 g/cm³. 2. Replacing convective tempering of PAN twists in thermooxidative treatment by conductive tempering reduces the treatment time by 3–4 times. __________ Translated from Khimicheskie Volokna, No. 5, pp. 11–15, September–October, 2005.