COALESCENCE AND THE INITIAL STAGE OF FORMATION OF NANOFIBERS BY THE "VAPOR–LIQUID–SOLID" SCHEME
S. A. Zhdanok, V. V. Martynenko, S. P. Fisenko, and S. I. Shabunya
It has been shown that the diffusion interaction of growing impurity clusters within catalytic nanodroplets determines the important geometric parameters of a nanofiber. The characteristic time of coalescence of the clusters has been found.
Keywords: mathematical modeling, Kelvin effect, supersaturation, radii of curvature, cluster, solubility.
STRUCTURAL CHANGES IN A CLAY-CONTAINING NANOCOMPOSITE WITH A DIFFERENT MOISTURE CONTENT CAUSED BY ITS DEFORMATION
E. A. Faitel’son, T. I. Glaskova, V. P. Korkhov, and A. N. Aniskevich
This paper presents the results of an investigation of the properties of a clay-containing nanocomposite with an epoxy binder under moisture-temperature and mechanical action. It has been established that whatever the moisture content, the nanocomposite crystallizes under the thermomechanical action (upon reaching the glasstransition
temperature). When the nanocomposite is heated to 70oC, the restructuring process is reversible,
and its heating to above 150oC leads to its amorphization. The presence of clay nanoparticles (up to 6 mass percent) does not influence the temperature of structural transitions of the nanocomposite and does not cause
a substantial strengthening effect. The sorbed moisture plasticizes the nanocomposite and decreases its glasstransition
temperature by 10oC. The specific features of the thermomechanical behavior of nanocomposites
upon their tensile prestrain or creep are due to the formation of an oriented structure. Their crystallization
begins at lower temperatures and with a higher degree of crystallinity than that of unloaded nanostructures.
Keywords: adsorption-active medium, microheterogeneity, X-ray structural analysis, morphological changes, induced
SOLUTION OF THE INVERSE PROBLEM FOR THE PARAMETERS OF PRIMARY
CARBON NANOPARTICLES FROM ELECTRON-MICROSCOPY DATA
E. A. Baranyshin UDC 546.26;662.421.2
From the data on the size of primary carbon particles formed in ethylene pyrolysis in a shock tube in the temperature range 2100–2800 K, calculation of their growth time and temperature is performed. It is shown that the growth time of primary nanosize soot particles does not exceed 7–10 μsec; they are heated up to temperatures hundreds of degrees higher than the gaseous-phase temperature, which is confirmed by the results of measuring the soot temperature.
Keywords: carbon nanoparticles, shock tube, ethylene, cluster temperature.
HEAT AND MASS TRANSFER IN PHASE TRANSFORMATIONS EXPERIMENTAL INVESTIGATION OF THE DYNAMICS OF THE PHASE TRANSITION BOUNDARY IN THE MOTION OF A HEATED NON-NEWTONIAN FLUID IN A CHANNEL
A. V. Basteev,a A. V. Dashkov,b O. V. Kravchenko,c
O. N. Repalova,d and V. V. Forfutdinova
The process of growth of the boundary crystallized phase in the motion of a heated non-Newtonian fluid in a channel with a cold wall has been studied experimentally. As the fluid, polypropylene with pseudoplastic properties was used. Experimental curves of the growth of the wall crystallized phase as a function of time were obtained for different values of the initial fluid melt temperature. The experimental value of the Nusselt number at the solid-liquid interface has been computed.
Keywords: crystallized layer, wall layer, crystallized phase, non-Newtonian fluid, nonlinear-viscous fluid, pseudoplastic.
NONEQUILIBRIUM PHASE TRANSFORMATIONS INDUCED BY DISLOCATION GLIDE IN PLASTIC DEFORMATION OF ALLOYS
I. K. Razumov UDC 669.112
It has been shown that in intense plastic deformation of alloys, dislocation glide gives rise to nonequilibrium phases or disperse structures. The phenomenon is due to the joint action of two factors: acceleration of diffusion and change in the chemical potential of the alloy components in the region of the dislocation core.
Keywords: intense plastic deformation, spinodal decomposition, Cottrell atmospheres, diffusion cutting, dissipative
TEMPERATURE FIELDS IN THIN WIDE-PROFILE PLATES OBTAINED FROM A MELT BY THE STEPANOV TECHNIQUE UNDER NONSYMMETRIC CONDITIONS OF GROWTH
A. V. Zhdanov,a A. V. Borodin,b
and M. V. Yudinb
A mathematical model is suggested allowing one to determine the temperature fields in thin wide-profile plates when growing them from a melt by the Stepanov technique depending on the asymmetry in the position of a growing crystal relative to the nearby screens, as well as on the difference between the surface temperatures of the left and right screens. The model contains the heat conduction equation and a system of integral
equations that connects the densities of radiant and temperature fluxes.
Keywords: Stepanov’s technique, temperature fields, radiation heat transfer.
CORRELATION BETWEEN THE SUPERCOOLING PARAMETERS OF A FREEZING MOIST MATERIAL AND THE TEMPERATURES OF TRANSITIONS TO THE PLASTIC- AND SOLID-FROZEN STATE AND ITS LONGEVITY
A. A. Konovalov UDC 624.139
The dependence of supercooling parameters of a freezing moist material on its properties and cooling temperature is discussed (using soil as the example). It has been shown that there is an approximate correlation between the supercooling temperature and the temperature at the interface between the solid-frozen and the plastic state, and between the supercooling period and the longevity in the frozen state. A formula for calculating the longevity by the supercooling parameters has been obtained.
Keywords: frozen soil, supercooling temperature, supercooling period, longevity, long-term strength.
MECHANISMS OF BOILING OF AN EMULSION WITH A LOW-BOILING DISPERSE PHASE
IN A TURBULENT FLOW OF A HOMOGENEOUS EMULSION
A. K. Rozentsvaig and Ch. S. Strashinskii UDC 532.529+536.24
A theoretical analysis of the time delay in the boiling of overheated drops in a turbulent flow of a homogeneous emulsion with a low-boiling disperse phase has been performed. Model relations determining the influence of the fluctuations of the velocity of a turbulent flow of an overheated emulsion on the formation of critical vapor bubbles in the disperse-phase drops have been derived. The initiation of formation of stable centers of nucleation of the vapor phase in an overheated emulsion by the factors determining the deformation and fragmentation of drops in it has been considered. The results obtained were compared with the corresponding
Keywords: emulsion, turbulent flow, disperse phase, overheated drops, vapor phase, initiation of nucleation.
INFLUENCE OF THE GROUND CAPILLARITY AND OF EVAPORATION FROM THE FREE
GROUNDWATER SURFACE ON FILTRATION FROM CANALS
E ′. N. Bereslavskii and N. V. Zakharenkova UDC 532.546
Mathematical models of certain groundwater flows from a canal in the presence of free-surface evaporation are considered on the basis of the two-dimensional theory of steady-state filtration. Mixed boundary-value problems of analytical-function theory are formulated and solved with the Polubarinova-Kochina method for studying such flows. Algorithms of calculation of the dimensions of the saturation zone in situations where, in filtration of water from a canal, the capillarity of its ground or the level of water in it are allowed for are based on these models. Using the obtained exact analytical dependences and numerical calculations, we made a detailed analysis of the structure and characteristic features of the modeled processes and of the influence
of all physical characteristics of the models on the dimensions of the saturation zone.
Keywords: filtration, groundwater, ground capillarity, evaporation, Polubarinova-Kochina method, Fuks linear differential equations, complex flow velocity, conformal mappings.
MATHEMATICAL SIMULATION OF METAL SOLIDIFICATION IN A WEDGE-LIKE
CASTING MOLD WITH ALLOWANCE FOR NATURAL CONVECTION
V. D. Aleksandrov,a N. N. Golodenko,a
V. V. Dremov,a and F. V. Nedopekinb
Using the finite difference method, a nonstationary problem of metal solidification in a wedge-like casting mold has been solved in a two-dimensional statement with allowance for natural convection. For isolated instants of time the positions of the solidification front, the profiles of temperature, horizontal and vertical velocity components, and of the stream function have been obtained.
Keywords: convection velocity, solidification, temperature profiles, casting mold, liquid phase, solid phase, heattransfer equation, phase transition, characteristic dimensions, velocity curl.
HYDRO- AND GAS DYNAMICS IN TECHNOLOGICAL PROCESSES VERIFICATION OF CHEMICAL REACTION RATE MODELS IN TURBULENT REACTING FLOWS AT SCHMIDT NUMBER CONSIDERABLY EXCEEDING 1
A. D. Chornyia and V. L. Zhdanovb UDC 532.517.4, 532.526.5
Relations widely used in numerical modeling describing the average rate of a chemical reaction have been analyzed. The spontaneous distributions of the mixture fraction and reaction products measured simultaneously in different cross-sections of the jet mixer under turbulent mixing of chemically reacting incompressible liquid media served as the basis for verification.
Keywords: laser-induced fluorescence, turbulent jet, cocurrent flow, mixture fraction, segregation coefficient, chemical reaction rate, probability density function.
CONTROL OF THE SELF-OSCILLATION OF AMPLITUDE OF VIBRATION COMBUSTION IN A LIQUID-PROPELLANT ROCKET ENGINE BY SOLVING THE SYSTEM OF EQUATIONS
THAT DESCRIBE THIS REGIME OF COMBUSTION
V. V. Gotsulenko UDC 629.7:533.6.001
Periodic solutions of the degenerate system of equations of nonstationary motion of a medium in a liquid-propellant rocket engine were obtained, with the aid of which the possibility of lowering the amplitude of the longitudinal self-oscillations of vibration combustion or their complete removal has been substantiated.
Keywords: degenerate system, limiting cycle, control of the amplitude, vibration combustion.
TRANSONIC FLOW OVER AIRFOILS AT ENERGY INPUT AND WITH ACCOUNT FOR THE REAL
PROPERTIES OF THE AIR
S. M. Aul’chenko, V. P. Zamuraev,
and A. P. Kalinina
We have investigated the influence of molecular (thermodynamic and transfer) properties of the air on the qualitative and quantitative characteristics of the gas-dynamic effects of pulsed-periodic energy input in transonic flow over airfoils. The influence of the transfer properties (viscosity) has been taken into account approximately within the boundary layer. It has been shown that qualitative estimates of the above effects do not depend on the account of molecular properties of the air, but the existence of internal degrees of freedom leads to a marked lowering of the temperature level as compared to the ideal gas model. Account of the viscosity somewhat decreases the energy input estimates. The influence of the airfoil shape on the aerodynamic characteristics at energy input has been investigated.
Keywords: transonic flow, airfoil, molecular properties of air, aerodynamic characteristics, energy input.
INFLUENCE OF THE GEOMETRICAL AND GASDYNAMIC PARAMETERS OF A MIXER ON THE MIXING OF RADIAL JETS COLLIDING WITH A CROSSFLOW
M. G. Ktalkherman, V. A. Emel’kin,
and B. A. Pozdnyakov
Results of investigation of the mixing of a system of axisymmetrical jets with a subsonic carrying flow in a cylindrical channel are presented. The main characteristics of the mixer were varied in wide ranges in the process of experiments. The regime of colliding jets was realized in the majority of experiments. The influence of individual factors on the quality of the mixing was considered. A combination of the mixer parameters within the ranges investigated, optimum for a high-quality mixing, has been determined. The experimental results
obtained were compared with the corresponding data of other authors.
Keywords: mixer, jets in a carrying flow, long-range interaction of jets, quality of mixing.
ON LOCALIZATION OF CONTACT SURFACES IN MULTIFLUID HYDRODYNAMICS
V. S. Surov UDC 532.529.5
Within the framework of the unified-equilibrium model of a multicomponent mixture that accounts for the forces of interfractional interaction, the problem of localization of contact surfaces is solved numerically in Euler variables. A finite-volume conservative scheme with the approximate Riemann solver HLLC was used in the calculations.
Keywords: single-velocity multicomponent medium, contact boundaries, approximate Riemann solver HLLC, numerical
OPTIMIZATION OF THE DEFLAGRATION-TO-DETONATION TRANSITION
A. A. Vasil’ev UDC 534.222.2+536.46+661.215.1
An analysis has been made of the methods of the optimizing the deflagration-to-detonation transition in fuel mixtures. Engineering formulas for designing accelerators of this process have been proposed. Certain experimental results on its optimization in plane and diverging waves, which were obtained with highly efficient accelerators, have been presented.
Keywords: combustion, detonation, deflagration-to-detonation transition, optimization.
HEAT AND MASS TRANSFER IN DISPERSION MEDIA HYDROGEN PRODUCTION WITH THE USE OF AN INDIRECT-HEAT-INPUT GASIFICATION SCHEME
V. A. Borodulya, G. I. Pal’chenok,
and S. V. Vasilevich
An experimental plant of productivity up to 10 kW for obtaining synthesis gas with a high content of hydrogen has been developed and realized. Experimental studies have been made, and the dependence of the composition of produced synthesis gas on the gasification chamber temperature, the catalyst content, and the moisture content of the raw material has been revealed.
Keywords: gasification, dolomite, experimental plant, synthesis gas.
HEAT TRANSFER IN GRANULAR BEDS IN RADIATIVE HEAT SUPPLY
Yu. S. Teplitskii and V. I. Kovenskii UDC 532.5
The basic regularities of stationary heat transfer throughout the space of an infiltrated granular bed in radiative heat supply in cocurrent-flow (solar collector 1) and counterflow (solar collector 2) regimes have been investigated within the framework of a two-temperature model. The boundary layer of the third kind for the skeleton of particles at exit from the bed has been formulated; this condition allows for the degree of turbulence of the heat-transfer-agent flow. A quasihomogeneity criterion making it possible to evaluate the thermal state of a two-phase system has been introduced. The approximation dependences for calculation of the active- portion length, the bed’s resistance, the solar-collector efficiency, and the average relative phase-temperature
difference have been established.
Keywords: granular bed, quasihomogeneity criterion, cocurrent flow, counterflow, radiative heat supply, bed’s resistance, degree of attenuation of radiation, degree of turbulence, heat-transfer agent.
DIA- AND PARAMAGNETOPHORESIS OF MICROPARTICLES
NEAR A SHORT MAGNETIZED CYLINDER
A. M. Zholud’ and B. E ′ . Kashevskii UDC 577.3
The motion of dia- and paramagnetic microparticles near a short magnetized cylinder and the conditions of registration and of spatial separation of diamagnetic particles by the value of magnetic susceptibility have been studied.
Keywords: magnetic separation, magnetophoresis, numerical simulation.
KINETIC AND STATISTICAL METHODS IN TRANSPORT THEORY MACROSCOPIC DESCRIPTION OF THE DYNAMICS OF DISTURBANCES OF A WEAKLY IONIZED
PLASMA UNDER HIGH-NONEQUILIBRIUM CONDITIONS
E. N. Perevoznikov and G. E. Skvortsov UDC 621.453/467.015.2
Consideration is given to the dynamics of disturbances of a charged weakly ionized plasma on exposure to a fairly strong electric field in the presence of high velocities and disturbance gradients. Equations for macroscopic description of the plasma are constructed by the projective-kinetic method; the general expressions for correlation functions and their related nonequilibrium kinetic coefficients are obtained. With the example of the correlation density function and the diffusion coefficient of a highly nonequilibrium plasma, the asymptotics
of its kinetic coefficients is considered.
Keywords: weakly ionized plasma, macroscopic description, disturbance dynamics, strong electric fields, highnonequilibrium
UNIVERSAL ALGORITHM FOR TESTING STATISTICAL HYPOTHESES WITH RESPECT TO THE DISTRIBUTION
E. V. Chernukho UDC 519.226
On the basis of the comparison principle, we have developed a universal algorithm for testing hypotheses,
making this procedure simple and transparent. The algorithm is based on the formula for calculating the
probability of filling the bucket of the experimental histogram by the probability distribution of the random
process source. It has been established that the probability of filling the bucket is described by the binomial
distribution. The relation of this formula to the order measure formula has been shown.
Keywords: testing of hypotheses, comparison principle, repetitive experiment, order statistics.
HEAT CONDUCTION AND HEAT TRANSFER IN TECHNOLOGICAL PROCESSES
INFLUENCE OF THE HEAT EXCHANGE BETWEEN THE OUTER SURFACE OF A PLANE-PARALLEL STRIP-FOUNDATION TRIBOUNIT AND THE ENVIRONMENT ON ITS TEMPERATURE
A. Yevtushenko and M. Kuciej UDC 536.12:621.891529.3
Asymptotics (for small and large times) for solving the thermal friction problem for a tribosystem consisting
of a plane-parallel strip sliding at a constant velocity on the surface of a semi-infinite foundation have been
found. The thermal strip-foundation contact is ideal, and on the outer surface of the strip convective heat exchange
with the environment takes place. The corresponding thermal problem of friction under braking has
also been solved. Numerical analysis has been performed for the materials of the frictional pair cermet layer–
cast iron foundation.
Keywords: heat generation by friction, temperature, heat exchange, drag braking.
TRACKING OF THE PRESET PROGRAM OF WEIGHTED TEMPERATURES AND RECONSTRUCTION OF HEAT TRANSFER COEFFICIENTS
V. T. Borukhov, O. I. Kostyukova,
and M. A. Kurdina
An approach to numerical solution of problems of reconstruction of heat transfer coefficients in nonlinear
nonstationary initial boundary-value problems based on a preset sum of weighted temperatures has been developed
Keywords: inverse problems, optimum control, nonlinear heat conduction equation, reconstruction of heat transfer
coefficients, sum of weighted temperatures, regularizer.
TEMPERATURE AND STRESS IN A CT3 STEEL PLATE DURING AIR-ARC CUTTING AND WELDING PROCESSES
F. I. Panteleenko and A. Heidari Monfared UDC 669.1
Although the air-arc cutting process has been widely used in material processing engineering, little is known
about the temperature and stress in the air-arc cutting of plates. Here, a three-dimensional finite element model
including the material removal and thermal effect of the arc is developed to study the temperature and stress
fields of a CT3 steel plate during the air-arc cutting and welding processes. The influences of the air-arc cutting
process on the initial stress field and of the welding process on the initial residual stress are of primary
importance. It is very important for researchers to clarify the temperature and stresses during welding and cutting
processes and to fully understand the mechanism of the influence of cutting and welding on the plate.
Keywords: welding, residual stress, finite element, numerical simulation.
ELECTRODYNAMIC PROCESSES IN A SURFACE LAYER IN MAGNETOABRASIVE POLISHING
N. N. Grinchik,a O. P. Korogoda,b
and N. S. Khomichb
A consistent physicomathematical model of the propagation of an electromagnetic wave in a heterogeneous
medium has been constructed with the use of the generalized wave equation and Dirichlet theorem. Twelve
conditions at the interfaces between adjoining media were obtained and substantiated without using, in an explicit
form, the surface charge and surface current. The conditions are fulfilled automatically in each section
of the heterogeneous medium and are conjugate, thus making it possible to use schemes of through counting
for calculations. The effect of the concentration of "medium-frequency" waves with length of the order of hundreds
of meters at the fractures and wedges of domains of size 1–3 μm has been established for the first time.
Keywords: polishing, electromagnetic field, electric double layer, induced surface charge, domains, vacancies,
DETERMINATION OF THERMOPHYSICAL PROPERTIES STRUCTURIZED SURFACE LAYERS OF NORMAL ALKANES
B. A. Altoiz and S. V. Kiriyan UDC 539.2:541.18
The elevated viscosity of micron interlayers of certain normal alkanes compared to their viscosity in the "volume"
is determined experimentally in shear flow using a rotational viscometer. The observed difference is
considered to be caused by the manifestation, in such interlayers, of structural inhomogeneity due to the presence
of structurized polymolecular surface layers on the substrates bounding them. The structural parameters
of such layers, i.e., their equilibrium initial thickness and "hydrodynamic strength," are calculated in the
model of a constant-viscosity layer. The measured effective viscosity of the interlayers diminishes with growth
in the shear-flow velocity, which is attributed to the "cutting" of the structurized layer. Surfactant doping of
the liquids leads to an increase in the effective viscosity of the interlayers, which is produced by the strengthening
of the layer structure.
Keywords: structurized surface layers, epitropic liquid crystals, viscosity, rheological model, normal alkanes.
IDENTIFICATION OF THE THERMOPHYSICAL CHARACTERISTICS OF MATERIALS
V. G. Zverev,a V. A. Nazarenko,b
and A. V. Teploukhovb
From a unified methodological standpoint, the coefficient of the inverse problem of determining the thermophysical characteristics of a material from temperature measurements at its depth in the approximation of a semi-infinite body, single-layer and two-layer (with a layer of an ideal conductor) plate of finite thickness has been solved. The proposed technique does not employ operations of the smoothing of experimental data and allows one to remove the restrictions on the choice of the heating regime of the specimen of the material and to expand the range of measurements by the Fourier number.
Keywords: thermophysical experiment, thermophysical characteristics, inverse heat conduction problem, semi-infinite
body, single- and two-layer plates.