Propagation of a one-spot spinning wave in a thick-walled cylinder under adiabatic conditions

Propagation of a one-spot spinning wave in a cylindrical specimen with a coaxial internal channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics [maximum temperature, longitudinal and circumferential (tangential) velocities, “pitch,” and time of rotation of the hot spot around the specimen centerline] are tracked for a specimen of a particular size with a varied channel radius, for specimens of different sizes with a fixed channel radius, and for specimens with a constant wall thickness. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 41–49, July–August, 2006.     

Layer-by-layer rupture of the jet in spinning chemical fibres in the deformation resonance mode

It was found that layer-by-layer rupture of liquid jets takes place when the fibre takeup speed is increased in conditions of deformation resonance, causing their thickness to decrease below the values assigned by the condition of continuity of flow. Layer-by-layer rupture of the jet is caused by the almost parabolic velocity profile which arises during flow of the spinning solution in the spinneret opening channel. Adjustment of the velocity profile by increasing the air gap is accompanied by a decrease in the difference between the rates of rupture of the outer and inner layers of the liquid. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna, No. 6, pp. 19–21, November–December, 1999.     

Effect of macroscopic heterogeneity of the medium on the solid-state combustion wave characteristics in thermally and chemically heterogeneous media

A macroscopically heterogeneous medium is modeled by a set of cylinders (rods) pressed from a mixture of solid reagents, which have coaxial cylindrical cores made from an inert material. A three-dimensional mathematical model describing propagation of combustion waves over one cylinder is studied by numerical methods. The influence of the distance between the centerlines of the neighboring cylinders and transverse sizes of the cylinders on characteristics of combustion waves propagating over a heterogeneous medium is considered. It is demonstrated that there exists an optimal distance between the inert rods, which ensures a much higher velocity of the combustion wave along the specimen than the theoretically predicted velocity of the classical combustion wave propagating over a solid specimen. New types of spinning waves are described, whose motion makes the high-temperature spot move inside the charge mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 39–49, May–June, 2008.     

Studies on melt-spinning process of hollow fibers

Profile development and dimensional change in the melt-spinning process of hollow fibers were studied using a finite element method, and a numerical simulation was compared with experimental results. The numerical simulation of a hollow-fiber spinning process was carried out by considering the changes in inner and outer boundaries. Initial dimensions of inner and outer radii were obtained by measuring the dimensions of extrudate at the extrudate swell point using a capturing device. Extrudate swell plays an important role in determining the initial dimensions of the inner and outer radii, but has less effect on the hollow portion at the die swell point. The effects of spinning variables on the hollow portion show that spinning temperature is the most critical variable in controlling the hollow portion, followed by mass throughput rate. Take-up velocity has relatively less effect. As the mass throughput rate and take-up velocity increase and the spinning temperature decreases, the hollow portion of as-spun fiber increases. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1209–1217, 1998     

Some characteristics of a spin combustion site and of the processes occurring in it

The investigated specimens were made by compression of titanium powder. They were burnt in a nitrogen atmosphere. Channels were detected below the specimen surface burnt in a spin regime. The dimension s of the spin combustion site were estimated, and the nitrogen pressure effect on the site dimensions was determined within the range 100–1800 torr. Data were obtained on the degree of metal nitrating and the phase composition of the layer, traversed by the spin site, and of the other specimen layers as a function of their distance from the surface. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 46–49, May–June 1988.     

Propagation of spherical gas filtration combustion waves in inert porous media

The behavior of spherical combustion waves of gases in inert porous media is described in terms of one- and two-temperature models. Parametric dependences are obtained for the wave velocity and acceleration and for the temperature of the gas and porous medium in the wave. It is shown that in a diverging spherical gas flow, combustion waves initiated at different radii of the sphere converge to the standing wave coordinater ^*, and in a converging flow, on the other hand, they diverge from it. The experimentally observed propagation behavior of spherical combustion waves is well described by the proposed models. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 60–66, January–February 1999     

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     

Detonation of a thin explosive layer in evacuated tubes

Detenation of thin layers of dispersed primary and secondary high explosives (HE) on the outer surface of glass and plastic tubes 0.6–3 mm in diameter was examined at an initial air pressure inside the tube of 0.1 MPa to 30 Pa. It is shown that, under these conditions, the air practically does not influence the detonation velocity, which for secondary explosives (PETN, RDX, and HMX), is lower than or approximately equal to the Chapman-Jouguet detonation velocityD _CJ for a homogeneous mixture of the same substances. Experiments with a primary HE (lead azide) revealed regimes with a wave velocity higher thanD _CJ and a varying reaction zone pattern. When tubes containing a layer of a secondary HE were filled with an explosive gas mixture, waves of a hybrid detonation with a velocity both higher and lower than that in the evacuated tubes was observed. In tubes with diameter 2–3 mm, detonation proceeded in a spinning regime over the entire range of the initial pressure and at a velocity higher thanD _CJ. It is concluded that in the evacuated tubes with a thin HE layer on the walls, ignition is transferred by the stream of hot detonation products moving at the head of the detonation wave. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 56–67, November–December 1998     

Combustion of pressed specimens of heterogeneous systems subjected to a constant axial mechanical load

The growth dynamics of the height of burning pressed specimens with the specimen ends subjected to a compressive force of constant magnitude is studied using the heterogeneous Ti+C+20% TiC system as an example. It is found that in the examined range of compressive forces 0.1–2 kg/cm², the growth of the height of the burning specimens with time obeys a linear law; under a compressive force of ≈0.1 kg/cm², the specimen height increases by ≈100%, and under a force of ≈2 kg/cm², it increases by about 25%. The method used to measure the growth dynamics of the specimen height during combustion proved a useful tool for the experimental determination of both the burning time of the specimens and the delay in the transfer of combustion through an obstacle. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 103–109, May–June, 2007.     

Flow of spinning solution through spinneret openings and deformation resonance

In flow of an anisotropic solution of poly-(p-phenylene terephthalamide) through the channels of spinneret openings in a stream at a distance of 0.7R from the axis of the channel, two layers are formed, and the outer layer is deformed 2.7 times more than the inner layer. Subsequent longitudinal deformation of the jet flowing out primarily causes a break in the outer layer, accompanied by a periodic change in the diameter of the jet, known as “deformation resonance”. Increasing the air gap causes expansion of the jet diameter, accompanied by a further decrease in the flow rate in the outer layer and a decrease in the fibre speed at which deformation resonance appears. The actual critical deformation, calculated as the ratio of the fibre take-off speed to the actual speed in the outer layer, remains constant, equal to 66±6, which is approximately equal to the limiting deformation of the jet of a solution of PPTA in the absence of resonance. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna. No. 3, pp. 19–22, May–June, 1999.     

Effect of gas pressure on the laws of propagation of spinning waves during filtration combustion

A three-dimensional mathematical model of filtration combustion with the combustion front propagating over a cylindrical specimen pressed from a powdered solid reagent and placed into an oxidizing medium is considered. Characteristics of spinning waves are studied for different pressures of the ambient gas. Steady waves of surface combustion are demonstrated to propagate over the specimen at low ambient pressures. For spinning waves formed at higher pressures, the characteristics may change nonmonotonically with increasing pressure, and the point with the maximum temperature may be located in the depth of the specimen.     

Mathematical model of continuous detonation in an annular combustor with a supersonic flow velocity

A two-dimensional unsteady mathematical model of a continuous spinning detonation wave in a supersonic incoming flow in an annular combustor is formulated. The wave dynamics in a combustor filled by a gaseous hydrogen-oxygen mixture is studied. The possibility of continuous spin detonation with a supersonic flow velocity at the diffuser entrance is demonstrated numerically for the first time; the structure of transverse detonation waves and the range of their existence depending on the Mach number are studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 83–91, November–December, 2008.     

Critical conditions of the combustion of compressed titanium specimen

Critical combustion conditions were investigated for compressed titanium specimens concerning the specimen density and the oxygen concentration in a O₂−Ar mixture. It was shown that there is a minimum specimen density at which combustion characteristics undergo a significant change. The completeness of combustion monotonically decreases with increase in density. Possible causes of the observed phenomena are considered. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 50–55, May–June 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.     

Effect of some spinning parameters and after-spinning processing regimes on the separating characteristics of hollow-fibre membranes

Two different directions for further research emerged from the studies conducted: increasing the time the fibres stay in the first spinning bath; this should lead to the creation of a higher quality surface layer and greater selectivity of pervaporation; continuing research on the creation of composite membranes; creating symmetric porous hollow-fibre membranes as substrate and applying a thin layer of PDMS on them to ensure selectivity of the membranes could be best here. Translated from Khimicheskie Volokna, No. 2, pp. 29–32, March–April, 1998. The research was sponsored by Khimservis Association.     

Variants of use of the modified Lindsley-Leont'eva method for chemical fibre spinning products

The mechanical instrument developed by I. S. Leont'eva for assessing the structural properties of products of cotton spinning by the Lindsley method can be used without structural changes with different methods for yarn made of chemical fibres with an average length in the ranges of 32–42, 57–107, and 124 mm. The use of the instrument and its modifications for correctly evaluating the structural products of products of spinning by the Lindsley method for the entire possible range of fibre lengths requires creating a base of the corresponding values of the fractional coefficients. The solution of these problems corresponds to the requirements of the manufacturers and consumers of chemical fibres for the length of staple fibres and the filament stapling length in expanding the yarn assortment. Moscow State Textile Academy. Translated fromKhimicheskie Volokna, No. 4, pp. 52–54, July–August, 1999.     

Conversion of methane through dielectric-barrier discharge plasma

Methane coupling to produce C₂ hydrocarbons through a dielectric-barrier discharge (DBD) plasma reaction was studied in four DBD reactors. The effects of high voltage electrode position, different discharge gap, types of inner electrode, volume ratio of hydrogen to methane and air cooling method on the conversion of methane and distribution of products were investigated. Conversion of methane is obviously lower when a high voltage electrode acts as an outer electrode than when it acts as an inner electrode. The lifting of reaction temperature becomes slow due to cooling of outer electrode and the temperature can be controlled in the expected range of 60°C–150°C for ensuring better methane conversion and safe operation. The parameters of reactors have obvious effects on methane conversion, but it only slightly affects distribution of the products. The main products are ethylene, ethane and propane. The selectivity of C₂ hydrocarbons can reach 74.50% when volume ratio of hydrogen to methane is 1.50. __________ Translated from Petrochemical Technology, 2007, 36(11): 1099–1103 [译自: 石油化工]     

Numerical simulation of the structure of two-dimensional gaseous detonation of an H2-O2-Ar mixture

A two-dimensional structure of detonation waves in an 2H₂+O₂+X Ar mixture is numerically studied in a wide range of initial pressures and degrees of dilution. Good qualitative agreement of the numerical results with experimental data is obtained. The effect of the method of initiation (by one or several sites, symmetric or asymmetric) on the steady structure of detonation waves is studied. The changes in the wave structure induced by variation of the channel width are examined. It is shown that the behavior of the two-dimensional wave structure is qualitatively different for mixtures withX=0 andX>0. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 5, pp. 93–103, September–October 1999.     

Shape-formation in the processes of self-propagating high-temperature synthesis of foams

Self-propagating high-temperature synthesis of cylindrical specimens of foam cermet with a relatively large length (l/D≫1) is performed. A Ti+0.6C mixture containing foaming agent Na₂B₂O₇·10H₂O was used. The initial compacts were enclosed in burning paper shells, which during self-propagating high-temperature synthesis made it possible to produce straight rods of foam ceramics, distinguished by an even surface. The dependence of the relative elongation of the specimens on the shell thickness was established. The possibility of controlling the shape of the foam SHS product by varying the slope of the combustion-front plane to the specimen axis was considered. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 121–122, May–June 1998.     

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.