Volume 94, №2


Limits of double-flow heat exchange and optimization of systems

Conditions for the minimum irreversibility of double-fl ow heat exchange have been obtained for various forms of kinetics. It has been shown that the obtained relations yield the realizability limits of the process; relations to calculate this limit have been derived. An algorithm to synthesize a double-fl ow heat exchanger with a minimum heattransfer coeffi cient at an assigned heat load has been proposed, which holds true for any heat-exchange kinetics. It has been shown that the obtained results make it possible to distribute heat loads and heat-transfer coeffi cients between double-fl ow heat exchangers in an arbitrary system for which the overall entropy production or the overall heat-transfer coeffi cient are minimum.
Author:  A. M. Tsirlin, L. G. Gagarina
Keywords:  double-fl ow heat exchange, heat-transfer coeffi cient, heat load, entropy
Page:  263-263

Correction of signals in a microbolometric array raising the validity of the measuring object's temperature. Part 1

Noncontact methods of imaging temperature fi elds, based on the registration of thermal radiation, are widely used in the study and control of thermal processes in different branches of human activities. To reduce uncertainty in measuring temperature with digital infrared imaging equipment, it is necessary to take into account a number of factors causing deviation of its readings from true values. In the paper, analysis is made of physical processes occurring in registration of thermal radiation by thermographs on the basis of microbolometric arrays and methods are proposed for correcting registered signals that make it possible to reduce uncertainty in measuring temperature using them. The fi rst part of the paper is devoted to considering the design of LWIR-range microbolometric arrays and the required corrections of registered signals making it possible to correctly interpret the obtained thermal images in a broad range of measured temperatures. The second part of the paper is devoted to algorithms of processing produced thermal imaging signals, and also to methods of accounting for the coeffi cient of thermal radiation of controlled surfaces and for the environmental radiation refl ected from them whose use makes it possible to improve the validity of temperature determination
Author:  V. A. Firago
Keywords:  thermal radiation, temperature fi elds, correction of thermal imaging signals, validity of temperature-fi eld measurement
Page:  272-285

Heat transfer of a stack of low-thermal-conductivity plates in cyclic heat exchange with cold and hot media

The authors have described a laboratory bench with a regenerative air heater and an automated system for control and measurement of the parameters of air fl ows and a packing. The bench is intended for investigating the heat transfer of a packing in the form of a stack of parallel plates under nonstationary conditions. A procedure for measuring the temperature of the fl ows of cold and hot heat-transfer agents with account taken of the inertia of thermocouples has been presented. A mathematical model of thermal processes in the fl ows of heat-transfer agents and the packing in cyclic heat exchange with the cold and hot heat-transfer agents has been developed. Results of computations of the changes in the temperatures of the heat-transfer agents and the plate with time and along the plate have been presented. Coeffi cients of heat transfer of the plate′s lateral surfaces have been calculated by the existing procedure and with the developed mathematical model. The calculation results have been generalized by the similarity equations. Coeffi cients of heat transfer of the plate′s end surfaces have been assessed
Author:  Yu. A. Kirsanov, D. V. Makarushkin, A. Yu. Kirsanov, A. E. Yudakhin
Keywords:  regenerative air heater, stack of plates, nonstationary processes, measurement, temperature, heat transfer
Page:  286-297

Direct method of calculating nonstationary temperature fields in bodies of basic geometric shapes

The authors propose a simultaneous solution to one-parameter heat-conduction problems for multilayer structures of basic (simple) geometric shapes with the direct (classical) method of investigation of the process of heat transfer. The presence of internal heat sources in the layers of such a structure and of ideal thermal contact between the layers with boundary conditions of the third kind on their bounding surfaces is assumed. In this connection, the authors solve the heat-conduction equation with a parameter having the meaning of the shape factor of a body. The reduction method, the concept of quasi derivatives, the present-day theory of systems of linear differential equations, the method of separation of variables, and a modifi ed Fourier method of eigenfunctions are used as a basis for the solution scheme. A model example of numerical calculation of the temperature fi eld in fi ve-layer structures (rectangular wall, a hollow cylinder, and a hollow sphere) is given.
Author:  R. M. Tatsii, M. F. Stasyuk, O. Yu. Pazen
Keywords:  reduction, quasi derivative, Cauchy matrix, method of eigenfunctions, shape factor of a body
Page:  298-310

Combined method of separation of variables. 3. Nonstationary heat conduction in solids with the first-kind boundary condition

The general idea of the combined method of separation of variables, as applied to the solution of problems on the nonstationary heat conduction in solid bodies canonical in shape (plate, cylinder, sphere) with the fi rst-kind boundary condition, is elucidated. Four effi cient schemes of calculating the eigenvalues of the Sturm–Liouville boundary-value problem are presented. An original method is proposed for determining initial amplitudes with a relatively high accuracy. Using the example of approximate solution of the heat-conduction problem for a solid cylinder with the fi rst-kind boundary condition, the signifi cant simplicity and, at the same time, the high effi ciency of the combined method of separation of variables is graphically demonstrated.
Author:  V. A. Kot
Keywords:  heat conduction equation, boundary-value problem, method of separation of variables, eigenvalues, eigenfunctions, approximate solution, integral relations, differential equation
Page:  311-344

Mathematical simulation of combustion of boron powder gas suspension

Based on a two-phase two-velocity model of a reacting gas-dispersed medium, a mathematical model of combustion of a boron powder gas suspension has been formulated. The results of numerical solution of the problem are presented. The infl uence of the composition of the gas suspension, its size, size distribution of particles, mass concentration of particles, as well as of the presence of aluminum powder in the suspension on the visible and normal velocities of fl ame propagation in the gas suspension, is shown. A comparison of the results of calculation with the well-known experimental and theoretical data is carried out. Satisfactory agreement of the predicted results with experimental data is shown.
Author:  A. Yu. Krainov, D. A. Krainov, K. M. Moiseeva, V. A. Poryazov, A. A. Khakimov
Keywords:  reacting gas suspension, boron and aluminum powders, burning velocity, mathematical simulation
Page:  345-356

Ignition and combustion of large coal particles in cold nitrogen–oxygen mixtures

Forced ignition and subsequent combustion of large coal particles in a cold air and oxygen are investigated experimentally. The critical value of the initial temperature (ignition temperature) of a particle of charcoal and of anthracite is estimated. On preliminary heating of the particle above the ignition temperature, a quasi-stationary mode of combustion is attained after a certain interval of time. For a charcoal particle, depending on the initial density of the particle, either a substantial change in its density or its invariability in the process of combustion in a cold air fl ow is observed. A relation is suggested allowing one to estimate the critical temperatures of ignition in cold gaseous mixtures depending on oxygen concentration and particle diameter. The absence of ignition of a large anthracite particle in air at room temperature is attributed to the larger value of the activation energy there than in the charcoal particle.
Author:  A. S. Chernenko and V. V. Kalinchak
Keywords:  coal particle, forced ignition, fi ring, combustion, cold gaseous mixtures, oxygen
Page:  357-364

Mathematical model of destruction of a thermoporoelastic medium

The work is devoted to the development of a mathematical model for describing the evolution of a thermoelastic medium with account for its destruction. The model is a modifi cation of the Biot three-dimensional model with two continua: a porous deformable skeleton and a mobile single-phase fl uid. The system of equations consists of fundamental mass, momentum, and energy conservation laws and is closed by thermodynamically coordinated determining relations. To derive the determining relations, use is made of the second law of thermodynamics that accounts for irreversible energy expenditures on the formation of a new surface of cracks. The form of the determining relations was obtained with the use of the Coleman–Noll procedure, which guarantees their thermodynamic coordination. The destruction of a medium is considered within the framework of the theory of continual destruction. To quantitatively estimate the degree of destruction, the damageability parameter is introduced, which is involved in all of the basic determining relations and, in particular, exerts its infl uence on the magnitude of elastic moduli. To determine the evolution of the damageability parameter, use is made of a kinetic equation. The applicability of the proposed model is shown with the example of calculation modeling heat carrier pumping into a thermoelastic medium
Author:  A. S. Meretina E. B. Savenkov
Keywords:  thermoporoelasticity, destruction, thermodynamic coordination, Coleman–Noll procedure
Page:  365-376

Features of inflow and pressure-buildup curves in porous fractured reservoirs

In the present work, by the methods of mathematical and numerical analysis, the author has investigated the regularities of the infl uence of the processes of mass exchange between rock clusters and fractures in porous fractured media on the form of infl ow and pressure-buildup curves and their time derivatives. It has been shown that in addition to the traditionally used parameter governing the relation of the compressibilities of the fracture space and the rock clusters, it is expedient to take account of the compressibility of the pore and fracture space under the action of the difference of pressures in the clusters and fractures. The author has established the governing parameters of the mass-exchange processes and their infl uence on the dynamics of pressure curves, which is manifested in the nonmonotonicity of the derivatives of pressurebuildup curves with respect to the Horner variable. It has been shown that this derivative reaching asymptotically the limiting value is preceded by the formation of the minimum region of the derivative. It has been noted that the nonmonotonic character of the derivatives may be fully or partially smoothed by the infl uence of the wellbore due to the compressibility of the fl uid in the below-packer zone of the wellbore and the infl uence of the skin factor, i.e., by the change in the permeability and porosity properties of the near-wellbore zone. The obtained results can be used for more correct interpretation of the data of hydrodynamic testing of wells in porous fractured reservoirs.
Author:  A. M. Svalov
Keywords:  hydrodynamic testing of wells, porous fractured rocks, infl ow curves, pressure-buildup curves, derivatives with respect to the Horner variable
Page:  377-383

Influence of the structure of the surface cellulose acetate layer on the transport characteristics of ultrafiltration composite membranes

The infl uence of the structure of the surface cellulose acetate layer on the transport characteristics of ultrafi ltration composite membranes is considered using the methods of IR spectroscopy and of scanning electron microscopy. The amorphous phase of ultrafi ltration cellulose acetate composite membranes is formed at a certain stage of the technological cycle of obtaining a composite membrane. IR spectra are presented where the forms of the absorption bands of valence vibrations of hydroxylic groups at ν = 3339.14–3366.2 cm–1 alter the asymmetry parameter from ~1 for an air-dry sample and to 0.79 for a water-saturated one, which allows the assertion of formation of volumetric supermolecular structure of a cellulose acetate layer of an air-dry sample by two types of hydrogen bonds and dipole– dipole interactions of carbonyl groups. The decrease of the asymmetry parameter to 0.79 of the absorption bands of hydroxylic groups and of the intensity of absorption bands of methyl groups by 2.56, 3.3, and 3.8 times in water saturated samples of membranes occurs because of the destruction of supermolecular structure and reorganization of hydrogen bonds between the active groups of cellulose acetate and molecules of water. The data obtained by the method of scanning electron microscopy allow one to note that the surface layer of ultrafi ltration membranes has an asymmetric pore structure. The surface layer of a membrane can be divided into two components: a selectively permeable layer with pores of small size and a pore substrate, in which the pores increase in their diameter as they approach the substrate
Author:  S. I. Lazarev, Yu. M. Golovin, I. V. Khorokhorina, D. S. Lazarev, D. A. Rodionov
Keywords:  surface layer, ultrafi ltration membrane, structure, hydrogen bonds, mesopores, transport characteristics
Page:  384-391

Assessment of the parameters of the anisotropic stratum and the near-wellbore region from the results of thermogasdynamic testing of vertical imperfect wells

The author proposes a method to interpret results of thermogasdynamic testing of vertical gas wells imperfect as far as the penetration degree of the stratum is concerned. A study is made of the infl uence of the parameters of the anisotropic stratum and the near-wellbore region on the curves of pressure and temperature at the wellbore. It is shown that when the penetration of the anisotropic stratum is incomplete, the parameters of the stratum and of the near-wellbore region can be assessed from the results of pressure and temperature measurements at the bore of the well after its startup
Author:  M. N. Shamsiev
Keywords:  thermogasdynamic testing, permeability anisotropy, radius of the near-wellbore region, inverse problem
Page:  392-401

Influence of water saturation on propagation of weak-intensity shock waves in bulk media

The paper presents the results of experimental investigations of the propagation of shock waves in media made up of sand and of glass balls with volume content of liquid in the pore space from 0 to 100%. It has been established that gas microbubbles on the surface of dispersed particles in the case of complete saturation of the porous medium with water exert a great infl uence on the propagation velocity of waves
Author:  A. T. Akhmetov, I. K. Gimaltdinov, L. F. Sitdikova, A. T. Akhmetov, I. K. Gimaltdinov, L. F. Sitdikova,
Keywords:  bulk porous medium, shock wave, water saturation, propagation velocity
Page:  402-407

A comparative analysis of amplitude and phase methods for measuring the moisture content of materials in the grain drying process flow

Assessment and comparison of the error in determining the moisture content of materials by the amplitude and phase superhigh frequency methods are considered. It has been revealed that when the mass of the controlled material is not constant, the error of the amplitude method is smaller than that of the phase one. As a result of the investigations, to control the moisture content of materials in a process fl ow, it is recommended to use the amplitude method of measurements.
Author:  P. M. Matyakubova, P. R. Ismatullaev, R. R. Kuluev
Keywords:  moisture content measurement, measurements, moisture content, error, amplitude, phase, method, device, mass, material, frequency, wave
Page:  408-414

Hybrid method of lattice boltzmann equations to model thermogravitational flows

A hybrid mathematical model has been developed in which the fl ow fi eld of a viscous incompressible medium is calculated by the method of lattice Boltzmann equations using the Bhatnagar–Gross–Krook approximation and a two-dimensional nine-velocity scheme, and free convective heat transfer is calculated by the fi nite difference method. The formulated approach to solving thermogravitational-convection problems has been verifi ed on numerical and experimental data of other researchers. From a comparative analysis, it has been established that the computational effi ciency of the hybrid mathematical model is 50 times higher than that of the traditional approach, which is based on the fi nite difference method and transformed "vorticity–stream function" variables.
Author:  A. É. Ni
Keywords:  method of lattice Boltzmann equations, fi nite difference method, Bhatnagar–Gross–Krook approximation
Page:  415-422

Enhanced heat transfer effectiveness using low concentration SiO2–TiO2 core–shell nanofluid in a water/ethylene glycol mixture

This paper assesses the heat transfer performance of nanofl uids containing a core–shell structure of SiO2 –TiO2 nanoparticles of low concentration in a mixture of water and ethylene glycol (EG) in a commercially available heat exchanger. For heat transfer analysis, 0–0.025% of SiO2 –TiO2 nanoparticles were employed in a fi nned-tube cross-fl ow heat exchanger (automobile radiator kit). The obtained results indicate that SiO2 –TiO2 particles have an amorphous structure and make it possible to increase the thermal conductivity as the nanoparticle fraction increases up to 0.04%. The nanofl uid characteristics (Reynolds, Nusselt, and Prandtl numbers) increase, leading to an increase in the convection coeffi cient. As the thermal conductivity and the convection coeffi cient increase, the total heat transfer improves. Finally, the heat transfer effectiveness increases linearly by 21% with 0.025% mass fraction of SiO2 –TiO2 in a water/EG-based fl uid.
Author:  I. M. Arsana, L. C. Muhimmah, G. Nugroho, R. A. Wahyuono
Keywords:  nanofl uid, SiO2 –TiO2, EG/water mixture, automobile radiator, heat transfer
Page:  423-430

Recycling of low-density polyethylene waste for synthesis of carbon nanotubes

The authors have presented results of synthesis of carbon nanotubes from low-density polyethylene. The synthesis was carried by thermal destruction of the polyethylene in a chemical-vapor-deposition unit. The process of decomposition of the polyethylene and the synthesis of carbon nanotubes were implemented in one stage in a triple-fi red furnace for chemical vapor deposition. Consideration has been given to the infl uence of temperature on the decomposition products of polyethylene in the range of temperatures 450–550o C. The gas- and vaporphase decomposition products of polyethylene, obtained at different temperatures, were investigated by the infrared spectroscopy method. It has been established that the necessary and suffi cient temperature of decomposition of polyethylene is 450o C. Carbon nanotubes were grown on a catalyst that represented cenospheres impregnated with a ferrous nitrate solution. On exposure to high temperatures, ferrous nitrate decomposes to form pure iron particles on the cenospheric surface, which are active sites of growth of carbon nanotubes. The formation of iron particles on the cenospheric surface upon the impregnation with ferrous nitrate and thermal treatment is confi rmed by the results of x-ray phase analysis. A semiquantitative analysis shows that the content of iron in the total catalysts mass amounts to about 2.3%. The synthesis gives rise to carbon nanotubes with diameters of 50–60 nm on the cenospheric surface. Thus, it has been shown that carbon nanotubes can be synthesized from low-density polyethylene waste.
Author:  G. T. Smagulova, N. Vassilyeva, B. B. Kaidar, N. Yesbolov, N. G. Prikhod′ko, Zh. Supiyeva, M. T. Artykbaeva, Z. A. Mansurov
Keywords:  carbon nanotubes, low-density polyethylene, decomposition, cenospheres, iron, infrared spectroscopy
Page:  431-436

Mathematical simulation of heat transfer and chemical reactions in an equilibrium dissociating gas

Results of investigations of the heat exchange in the turbulent fl ow of nitrogen tetroxide in a cylindrical channel are presented. The equilibrium stage of the dissociation reaction N2O4 - 2NO2 was considered. It was established that an increase in the temperature of the wall of the channel leads to an intensifi cation of the chemical reaction proceeding in the N2O4 fl ow and causes the absorption of the heat, transferred from the channel wall, in this fl ow to increase, with the result that the temperature of the near-wall layers and the thickness of the thermal boundary layer in the chemically reactive gas fl ow decrease to a level lower than those of a chemically inert heat-transfer agent. It is shown that the use of a dissociating heat-transfer agent in a short channel is advantageous in the case where the rate of its fl ow is small, and, to increase the effi ciency of heat exchange in a high-velocity fl ow of such an agent, it is necessary to increase the length of a heat exchanger. Approximation formulas for determining the criteria of heat exchange in fl ows of chemically inert and reactive gases have been obtained.
Author:  O. V. Matvienkoa, and P. S. Martynov
Keywords:  heat exchange, chemical reaction, dissociation, boundary layer, computational hydrodynamics
Page:  437-449

Complex investigation of nonstationary flow with shock waves in the working path of a hypersonic ramjet engine

Results of a complex experiment-calculated investigation of the structure of a nonstationary gas fl ow in the working path of a hypersonic ramjet engine are presented. Methods of experimental determining the pressure and temperature distributions over the wall of an axisymmetric channel of complex geometry with a sudden widening are proposed and described. The problem on the gas fl ow over a ramjet engine positioned in a wind tunnel was solved.
Author:  A. N. Ishchenko, E. A. Maslov, N. P. Skibina, and V. V. Faraponov
Keywords:  experimental investigation, mathematical simulation, ramjet engine, shock wave, drainage tests, thermometric method
Page:  450-457

On the theory of forced mixing of hydrocarbon fluids in storage systems

The elementary scheme and the theory of mixing of two fractions of hydrocarbon fl uids in a tank using jet apparatuses (ejectors or jet pumps) have been considered. Equations have been presented that describe fl ows used in actual practice in the devices and make it possible to track the process of mixing in the stage of injection and in the subsequent stage of mixing in the jet turbulent fl ow of a mixture fl owing out of the ejector
Author:  V. Sh. Shagapov, É. V. Galiakbarova
Keywords:  ejector, characteristic equation, turbulent jet, forced circulatory convection
Page:  458-458

Enhancement of heat transfer during turbulent flow in plane and circular nonseparating diffusers

Consideration is given to the possibility of enhancing heat transfer in circular and plane nonseparating diffusers with small opening angles. Numerical modeling of the heat transfer was performed with the three-parameter differential turbulence model supplemented with the transfer equation for the turbulent heat fl ux. It has been show that at the same opening angle, the Nusselt number in the circular diffuser is much higher than that in the plane diffuser, with this excess growing with opening angle. However, the Reynolds analogy factor for the circular diffuser is only slightly higher than that for the plane one. A study has been made of the infl uence of the Reynolds number, the diffuser length, and the Prandtl number of the heat-transfer agent. It has been shown that the minimum effect of heat-transfer enhancement is attained for gases with a small Prandtl number and depends weakly on the Reynolds number and the diffuser length.
Author:  Enhancement of heat transfer during turbulent flow in plane and circular nonseparating diffusers
Keywords:  enhancement of heat transfer, circular diffuser, plane diffuser, Reynolds analogy factor
Page:  467-478

Resonance infrasound jet-edge generator and its amplitude–frequency characteristics

The infl uence of the geometric and regime parameters of a resonance infrared jet-edge generator on the formation, in its resonance tube, of a sound fi eld with a predominant discrete tone at the fundamental frequency of the generator resonant cavity was investigated. A parametric investigation of the self-sustained oscillation processes arising in the resonance tube of the generator as a result of the interaction of a subsonic gas jet and a supersonic one with its resonant cavity has been performed. The nonstationary structure of the gas fl ow inside this cavity, characteristic of the self-sustained oscillation interaction of a gas jet with an obstacle, is discussed. Prominence is given to the study of the pattern of the gas fl ow inside the resonant cavity and the amplitude-frequency characteristics of the wave process in it. Recommendations for designing a resonance infrasound jet-edge generator with regard for its use in actual practice are given.
Author:  K. N. Volkov, V. N. Emel′yanov, A. V. Efremov, and A. I. Tsvetkov
Keywords:  jet-edge generator, Hartmann effect, supersonic gas jet, noise generation, self-sustained oscillation process.
Page:  479-489

Focusing of a compression wave at the boundary of a bubble liquid

An analysis of the focusing of an acoustic wave in a cylindrical channel fi lled with a pure liquid and a bubble liquid, separated by a spherical surface, as a result of its refraction at this interface is given. The infl uence of the frequency of an acoustic wave propagating in such a liquid–gas mixture as well as the radius of the bubbles and their volume content in it on the distance of focusing of this wave in the mixture was investigated. The conditions under which the focal distance of the acoustic lens formed in a liquid–gas mixture takes a maximum and a minimum values and an acoustic wave propagating in this mixture is focused or scattered in it were determined.
Author:  I. K. Gimaltdinov, E. Yu. Kochanova
Keywords:  focusing, acoustic lens, bubble medium, pure liquid, spherical interface
Page:  490-495

Distinctive features of the wave process in the well casing under implosion

A numerical study has been made of the wave process in the casing string of the well, which is initiated by the difference of pressures in the imposition device and the well fl uid surrounding it. To describe the implosion process, a mathematical model has been proposed that takes account of the presence of two phases, viscous effects, the compressibility of the gas, nonstationarity, heat transfer, turbulence, and other factors. The basic parameters of the implosion process have been calculated. The infl uence of the implosion-device length on generated rarefaction and compression waves in the well fl uid has been established
Author:  I. V. Morenko
Keywords:  implosion technology, well casing, volume-of-fl uid method
Page:  496-502

Physical processes occurring in treating a substrate and depositing nanocoatings on it by a laser–plasma method

With the aim to simplify the automation of the process of sputtering nanocoatings by a laser–plasma method in vacuum, it is suggested to obtain an ion fl ow from a laser plasma and smoothly regulate the energy of ions and the density of their fl ow with the aid of the electric fi eld potential. In treating the substrate surface by ion streams, the regimes of etching the surface have been determined, as well as creation of a pseudodiffusional layer of the target material in the near-surface zone of the substrate, and deposition of the laser target material on the substrate.
Author:  V. K. Goncharov, A. A. Pekhota, M. V. Puzyrev
Keywords:  laser plasma, ion fl ows, nanocoatings
Page:  503-508

Density, velocity of sound, and derived properties of cyclohexane and decalin in a wide range of temperatures and pressures

An experimental study has been made of the density and the velocity of sound for liquid decalin and cyclohexane in the range of temperatures 298.15–433.15 K and pressures 0.1–100.1 MPa. Parameters of equations have been obtained that describe the dependences of the specifi c volume of liquid decalin and cyclohexane on their temperature and pressure and of the isobaric heat of these substances on their temperature at atmospheric pressure. The density, the velocity of sound, the isobaric and isochoric heats, the isobaric expansion coeffi cient, and the coeffi cients of isentropic and isothermal compressibilities of liquid decalin and cyclohexane have been determined in the range of temperatures 298.15–433.15 K at pressures to 100 MPa.
Author:  A. P. Shchemelev, V. S. Samuilov, N. V. Golubeva, O. G. Poddubskii
Keywords:  decalin, cyclohexane, density, velocity of sound, thermodynamic properties
Page:  509-519

Experimental investigation of the process of aviation kerosene dehydration in a fuel tank

The results of experimental investigations of the dehydration of aviation kerosene TS-1 in a model tank of volume 1.8 m3 are presented. The experiments were carried out under conditions simulating the regimes of a passengercarrying airplane fl ight at pressures 20–110 kPa and temperatures from –20 to +20o C. The dehydration of kerosene was made by bubbling air enriched with nitrogen with a 10% volume fraction of oxygen at its specifi c consumption of 0.0002–0.0007 s–1. A decrease in the concentration of the dissolved water to the values ensuring the absence of phase transitions in the water–kerosene system at temperatures down to –30o C has been established. The concept of using on-board systems of generation of inert gases for dehydrating the kerosene in the fuel tank of an airplane under cruising fl ight conditions has been confi rmed.
Author:  É. L. Kitanin, V. L. Zherebtsov, M. M. Peganova, S. G. Stepanov, D. A. Bondarenko
Keywords:  aviation fuel, dehydration, bubbling, on-board system, fl ight conditions
Page:  520-524

Dynamic stability of a composite cylindrical shell with linear-variable thickness under pulsed external pressure

Equations have fi rst been obtained for dynamic stability of a composite cylindrical shell with linear-variable thickness under the action of axial forces and external pulsed pressure. The solution of these equations along the axial coordinate was found in the form of trigonometric series. Using the Bubnov–Galerkin method the problem was reduced to an infi nite system of ordinary differential equations that is reduced to an infi nite system of homogeneous algebraic equations in the form of temporal trigonometric series. By reducing the obtained system and equating the reduced matrix determinant to zero, a characteristic equation was obtained to determine the critical frequencies of external pressure pulsations. A numerical example has been used to investigate the effect of the axial force and the length of a composite shell of linear-variable thickness on the boundaries of its instability. It has been shown that, in using medium-integral thickness of the shell in calculations, the error in identifying the area of this region may reach high values, which is indicative of the current importance of solving the problem of dynamic stability of a composite cylindrical shell with a linear-variable thickness in terms of weightwise improvement of aircraft. The developed mathematical model expands signifi cantly the range of solvable problems and makes it possible to calculate the dynamic stability of orthotropic cylindrical shells with linear-variable thickness
Author:  V. N. Bakulin, A. Ya. Nedbai
Keywords:  dynamic stability, composite cylindrical shell, linear-variable thickness, external pulsed pressure
Page:  525-533

Microstructure and mechanical properties of Bi27In38Sn35 foil produced by rapid solidification

Investigations into the microstructure of Bi27In38Sn35 alloy have shown that an increase in the melt cooling rate from 102 to 105 K/s leads to a change in the solidifi cation mechanism. At a melt cooling rate of 102 K/s, we observe consecutive solidifi cation of the dendrites of the Sn4In phase, and then that of BiIn and BiIn2 phases in the interdendritic space. Bi27In38Sn35 foil produced by rapid solidifi cation consists of BiIn, BiIn2, and Sn4In phases forming a lace-like structure. The foil′s chemical composition determined by X-ray spectral analysis was constant in thickness. Alloy foil phase grains have a microcrystalline structure and texture. The aging of rapidly solidifi ed foil at room temperature causes size enlargement in phase and grain precipitations, which determines the change in its physical properties. Foil aging causes an increase in microhardness and affects tensile deformation: there is consolidation of rapidly solidifi ed alloy at the initial stage of deformation and a reduction in its plasticity
Author:  S. V. Gusakova, V. G. Shepelevich,O. V. Gusakova
Keywords:  bismuth, indium, stannum (tin), lead-free solder, grain, texture, phase, microhardness, specifi c surface.
Page:  534-540

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