HEAT AND MASS TRANSFER IN COMBUSTION PROCESSES KINETIC MECHANISM OF COMBUSTION OF HYDROGEN–OXYGEN MIXTURES
G. Ya. Gerasimov and O. P. Shatalov
Based on the analysis of the databases published in the scientifi c literature and concerned with the reaction rate constants in the H2/O2 system, a new kinetic mechanism is suggested for describing the processes of ignition, combustion, and detonation in ydrogen–oxygen gaseous mixtures. Attention is mainly focused on consideration of a low-temperature region (T < 1000 K) where a chain of reactions of the formation and subsequent decomposition of hydrogen peroxide plays the major role in the system ignition. The proposed mechanism has been tested by comparing computational results with available data on measurement of the ignition-delay time in shock tubes.
Keywords: hydrogen–oxygen mixtures, combustion, kinetic mechanism, induction time, databases on reaction rate constants.
ON THE DEEPENING MECHANISM OF THE SITE OF PEAT COMBUSTION
A. M. Grishin, V. P. Zima, and D. P. Kasymov
The present paper considers, on the basis of the available data and experimental studies, a variant of deepening of
the combustion site with account for the botanical composition.
Keywords: combustion process, peat, botanical composition, combustion conductors.
METHANE-TO-HYDROGEN CONVERSION IN A REVERSIBLE FLOW FILTRATION COMBUSTION REACTOR AT A HIGH PRESSURE
Yu. M. Dmitrenko and P. A. Klyovan
The noncatalytic process of partial oxidation of methane to syngas in a reversible fl ow fi ltration combustion reactor at high pressures has been considered. The infl uence of the operating pressure in the reactor on the main parameters of the conversion process — the maximum temperature in the combustion wave and the composition of reaction products — has been investigated experimentally. Investigations were carried out for fuel mixtures of different calorifi c powers at pressures of up to 6.0 bars. It has been shown that at a fi xed value of the specifi c mass fl ow of the fuel mixture the effi ciency of the process of methane-to-syngas conversion decreases with increasing pressure in the reactor.
Keywords: conversion of methane, syngas, partial oxidation reaction, superadiabatic effect, fi ltration combustion wave, inert porous packed bed, reversible reactor.
NANOSIZED SUBSTRUCTURE OF HEAT-TREATED HIGH-STRENGTH CAST IRON
S. A. Chizhik,a T. A. Kuznetsova,a A. L. Khudolei,a A. I. Komarov,b V. I. Komarova,b and M. S. Vasilenkoc
This paper presents the results of investigating the microstructure of high-strength VChTG cast iron by the methods of scanning electron and atomic-force microscopy and x-ray phase analysis. A nanosized substructure of ferrite, perlite, and graphite phases of the cast iron has been revealed. An ordered sandwich multilevel structure of ferrite in the initial VChTG in the form of steps of width 400–600 nm and height about 100 nm consisting of bands of width 30 nm and interband height 3–10 nm has been established. It has been shown that the width of cementite lamellae in perlite varies from 200 to 400 nm, and the lamellae themselves consist, in turn, of sublamellae of width 30 nm. Graphite inclusions consist of layered crystallites of diameter 5–200 nm with a thickness of individual layers of 0.7–1.4 nm. Upon heat treatment the size of bainite subgrains is 100–300 nm. It has been shown that there is s relation between the size of the shift of subgrains for heat-treated VChTG revealed by atomic-force microscopy and microdistortions of the ?-phase lattice determined by x-ray analysis.
Keywords: high-strength cast iron, heat treatment, phase composition, morphology, bainite structure.
DEPOSITION OF CU AND AL NANOSIZED FILMS IN A VACUUM BY A LASER METHOD
V. K. Goncharov, G. A. Gusakov, and M. V. Puzyrev
Copper and aluminum nanosized fi lms have been obtained. The fi lms were deposited on substrates in a vacuum by a laser-plasma method. The structure of the fi lm surfaces has been determined depending on the power density of the laser radiation acting on metal targets. The thresholds of evaporation for aluminum and copper under the action of a nanosecond laser pulse have been found.
Keywords: laser-plasma deposition, nanosized metal fi lms, erosive laser plasma.
CONTROLLING THE PROCESS OF TITANIUM DIOXIDE NANOPARTICLE GROWTH IN A CONTINUOUS-FLOW PLASMA-CHEMICAL REACTOR
S. M. Aul'chenko
The formation and growth of titanium dioxide nanoparticles in the working zone of a plasma-chemical reactor were modeled and the effect of the hardening air jet parameters in the reactor on the size of the particles formed in it has been studied. The results of modeling were compared with relevant experimental data.
Keywords: titanium dioxide, titanium tetrachloride, plasma-chemical reactor, one-velocity multicomponent medium, quasi-gas-dynamical system of equations, homogeneous and heterogeneous reactions, coagulation.
INVESTIGATION OF THE SORPTION ACTIVITY OF MULTILAYER CARBON NANOTUBES AND AMORPHOUS CARBON FORMED FROM REGENERATIVE VEGETABLE RAW MATERIALS
D. V. Onishchenko,a V. P. Reva,b V. V. Chakov,b and V. V. Petrovc
Complex studies of the sorptive properties of carbon materials obtained from regenerative vegetable raw materials have been made. The possibility of using such materials as enterosorbents has been considered.
Keywords: regenerative vegetable raw material, peat moss, pyrolysis, amorphous carbon, mechanoactivation, multilayer carbon nanotubes, sorption capacity, enterosorbents.
BROWNIAN DIFFUSION AND TRANSFER OF NANOPARTICLE BEAM BY A GAS FLOW
D. A. Takopulo and S. P. Fisenko
The infl uence of the cooling of a gas-carrier fl ow in a cylindrical channel on the spreading of a beam of nanoparticles moving in this fl ow was theoretically investigated.
Keywords: free-molecular approximation, thermophoresis, aerodynamic focusing.
HEAT CONDUCTION AND HEAT TRANSFER IN TECHNOLOGICAL PROCESSES
SIMULATION OF CONVECTIVE HEAT EXCHANGE IN THE SUBDUCTION ZONE
S. V. Solov'ev
Results of the mathematical simulation of the convective heat exchange in the process of movement of a lithospheric plate colliding with a continental plate and submerging into the mantle in the subduction zone under conditions where the free fall acceleration in the mantle changes by the linear law are presented.
Keywords: convective heat exchange, subduction, lithosphere, earth’s mantle.
OPTIMIZATION OF THE REQUIRED TEMPERATURE OF CONTACT SOLDERING OF ELECTRONIC DEVICES
V. N. Shtennikov and V. D. Seleznev
UDC 621.372; 621.791.3
This paper presents the results of a complex of experimental and theoretical studies aimed at improving the quality of soldering electronic devices by optimizing the design-technological parameters.
Keywords: engineering physics, devices, soldering, temperature, heat conduction, time.
OPTIMIZATION OF THE RIBBING OF A NEW HEAT EXCHANGE SURFACE OF FLAT-OVAL TUBES
E. N. Pis'mennyi, P. I. Bagrii, A. M. Terekh,and A. V. Semenyako
We propose a method for determining the effi ciency and optimum dimensions of ribs of a new highly developed heat exchange surface in the form of fl at-oval tubes with partial transverse ribbing. We used an approximate approach based on simplifi ed equations for right rectangular ribs on a fl at base.
Keywords: heat exchange surface, ribbing, effi ciency coeffi cient, optimization.
HEAT AND MASS TRANSFER IN NATURAL DRAFT COOLING TOWERS
M. M. Hemmasian Kashania and K. V. Dobrego
Cooling towers (CTs) are important units in the vast majority of power plants. They have been intensively investigated for the last 70 years. The abundance of works makes diffi cult to "see" the total area of investigations of CTs and to fi nd the most urgent and important results. This article contains a compact overview of contemporary publications (for the last 11 years) in the area of heat and mass transfer in CTs, especially in natural draft wet cooling towers (NDWCT), and of related phenomena. Attention is specially paid to modern numerical computational investigations.
Keywords: heat and mass transfer, cooling tower, thermal performance.
HEAT AND MASS TRANSFER IN DISPERSED AND POROUS MEDIA
ANALYSIS OF THE OPERATION OF A PACKED RECTIFYING COLUMN IN THE PROCESS OF BINARY MIXTURE SEPARATION
A. I. Moshinskii
On the basis of a continuum mathematical model, the operation of a packed rectifying column in the stationary (continuous) and nonstationary (periodic) regimes in the process of binary mixture separation under certain conditions has been analyzed. We have considered examples of the realization of the above process, for which analytical expressions convenient for calculations have been obtained.
Keywords: mass transfer, equilibrium function, approximation, rectifi cation.
ON FILTRATION OF A LIQUID FROM A FOUNDATION PIT FENCED WITH SHEET PILES
E. N. Bereslavskii
Liquid fl ow from a foundation pit fenced with symmetric Zhukovskii sheet piles in the presence of a well-permeable head water-bearing horizon and infi ltration onto the free surface is considered within the framework of plane steadystate fi ltration. For studying this fl ow, a mixed multiparametric boundary-value problem of the theory of analytical functions is formulated and solved with the Polubarinova-Kochina method. An algorithm of calculation of the characteristic dimensions of the fl ow diagram is developed based on this model. Results of numerical calculations and an analysis of the infl uence of all physical parameters of the model are given. Limiting cases of motion are noted which are related to the absence of upthrust in the well-permeable underlying bed and to the transformation of the foundation pit into a submergence band semiinfi nite on the left.
Keywords: fi ltration, groundwater, Zhukovskii sheet pile, infi ltration, complex-fl ow velocity, conformal mappings, Polubarinova-Kochina method.
MOISTURE EXCHANGE IN DRYING NATURAL FABRICS IN A MICROWAVE ELECTROMAGNETIC FIELD
A. I. Ol'shanskii, V. I. Ol'shanskii, and S. V. Zhernosek
We present the results of investigation of the kinetics of drying fabric by a superhigh-frequency current. Experimental dependences are given for determining the time of drying and heat fl ux densities.
Keywords: electric fi eld intensity and frequency, permittivity, loss tangent, Pomerantsev number.
MIXED CONVECTION IN NON-NEWTONIAN FLUIDS ALONG A VERTICAL PLATE IN A LIQUID-SATURATED POROUS MEDIUM WITH MELTING EFFECT
A boundary-layer analysis is presented for the problem of mixed convection in a fl ow of a non-Newtonian fl uid from a vertical plate in a liquid-saturated porous medium in the presence of the melting effect. Aiding and opposing external fl ows are considered. The power-law model for non-Newtonian fl uids is used. After a suitable coordinate transformation, the governing boundary-layer equations are reduced to nonlinear coupled differential ones which are solved numerically by employing an implicit fi nite difference scheme. A discussion of the effect of the viscosity index and melting parameter on the surface heat transfer rate, as well as on the temperature and velocity distributions, is presented. It is shown that melting decreases the local Nusselt number. A comparison with previous published results at various values of the governing parameters for a Newtonian fl uid reveals an excellent agreement.
Keywords: melting, non-Newtonian fl uid, phase change, aiding and opposing fl ows, porous medium, mixed convection.
HYDRODYNAMICS IN TECHNOLOGICAL PROCESSES
THEORETICAL PREREQUISITES FOR MAGNETODYNAMICAL DETERMINATION
OF THE VISCOELASTIC PROPERTIES OF A FLUID
S. B. Kashevskii
A study has been made of the magnetic dynamics of high-coercivity low-magnetic microspheres suspended in a Maxwell–Voigt viscoelastic fl uid subjected to the action of an a.c. magnetic fi eld which is small compared to the coercive force of the microspheres. It is shown that the character of the response of these microspheres to the action of magnetic fi eld depends basically on the rheological properties of the fl uid — this serving as a basis for the magnetodynamic method of rheometry.
Keywords: magnetodynamics, viscoelasticity, high-coercivity low-magnetic microspheres.
ANALYSIS OF ERRORS OF MULTIBLOCK COMPUTATIONAL TECHNOLOGIES BY THE EXAMPLE OF CALCULATING A CIRCULATION FLOW IN A SQUARE CAVITY WITH A MOVING COVER AT RE = 103
S. A. Isaev,a A. G. Sudakov,b P. A. Baranov,b Yu. V. Zhukova,c and A. E. Usachovd
The errors of multiblock computational technologies realized in different versions of the VP2/3 package and involving the use of structured computational meshes of the H and O types with superposition were methodically investigated by the example of solving the problem on a circulation fl ow of an incompressible viscous fl uid in a square cavity with a moving cover at a moderate Reynolds number of ~103. A comparison of the numerical estimations of the integral and extremum local characteristics of the indicated fl ow, made with the use of composite and multiblock meshes with varying densities and near-wall steps, has shown that it is reasonable to use multiblock computational technologies with linear interpolation in the calculations with conversion of parameters from mesh to mesh.
Keywords: circulation fl ow, cavity, calculation, procedure of pressure correction, Rhie–Chow approach, multiblock computational technologies, VP2/3 package.
NODAL METHOD OF CHARACTERISTICS IN MULTIFLUID HYDRODYNAMICS
V. S. Surov
Within the framework of a generalized equilibrium model of a multicomponent mixture in which the forces of interfractional interaction are taken account of, the problem of localization of contact surfaces is solved in Euler variables with the nodal method of characteristics.
Keywords: one-velocity multicomponent mixture, contact boundaries, hyperbolic systems of partial differential equations, nodal method of characteristics, numerical simulation.
NODAL METHOD OF CHARACTERISTICS FOR CALCULATING FLOWS OF A MULTIVELOCITY HETEROGENEOUS MEDIUM
V. S. Surov
This paper describes a nodal method of characteristics intended for integrating one-dimensional equations of the model of a multivelocity multicomponent mixture with a gas-dynamic spatial grid.
Keywords: multivelocity multicomponent medium, hyperbolic system of equations, nodal method of characteristics, numerical modeling.
EXPERIMENTAL STUDY OF NONSTATIONARY REGIMES OF ASCENT OF A SINGLE BUBBLE
V. A. Arkhipov, I. M. Vasenin, and A. S. Usanina
Results of experimental study of the dynamics of ascent of a single spherical bubble in a viscous fl uid at small Reynolds numbers (Re < 1) have been presented. A refi ned empirical dependence has been obtained for the resistance coeffi cient in a stationary regime of motion of the bubble. The infl uence of nonstationary and "hereditary" effects on the dynamics of ascent of the bubble has been evaluated. A substantial infl uence of the Basset force on the characteristic of a nonstationary regime of motion of the bubble, in particular, on the characteristic time of dynamic relaxation, in the region of small Reynolds numbers has been shown.
Keywords: bubble, viscous fl uid, Reynolds number, nonstationary regime, Basset force, experimental study.
METHOD OF MEASURING THE QUANTITY OF AIR LIBERATED IN AVIATION FUEL FLOW AT LOW PIPELINE PRESSURE
E. L. Kitanin,a E. E. Kitanina,a V. A. Zherebtsov,b O. A. Merkulov,b,* M. M. Peganova,b D. A. Bondarenko,c and D. Morrisond
This paper presents the results of experimental studies of the quantity of air liberated in the fl ow of aviation fuel in the pipe at a low pressure. Experiments were carried out in the pressure range from 0.2 to 1.0 bar, and the temperature was varied from –20 to +20oC. We propose a method for determining the mass concentration of air dissolved in the fuel measured with the help of a chromatograph. An attempt to use an optical method for measuring the gas content of the fl ow has shown that it is useful in combination with a chromatographic method needed to calibrate the optical scheme.
Keywords: experiment, method, air liberation, chromatograph, aviation fuel, low pressure, two-phase fl ow, gas content.
STUDY OF THE EXACT ANALYTICAL SOLUTION OF THE EQUATION OF LONGITUDINAL WAVES IN A LIQUID WITH ACCOUNT OF ITS RELAXATION PROPERTIES
I. V. Kudinov and V. A. Kudinov
A mathematical model of elastic vibrations of an incompressible liquid has been developed based on the hypothesis on the fi nite velocity of propagation of fi eld potentials in this liquid. A hyperbolic equation of vibrations of such a liquid with account of its relaxation properties has been obtained. An exact analytical solution of this equation has been found and investigated in detail.
Keywords: wave equation, Hooke?s law, Newton?s second law, vibration of an elastic medium, infi nite and fi nite velocities of propagation of disturbances, relaxation properties of a medium, method of separation of variables, exact analytical solution.
EFFECT OF WATER COMPRESSIBILITY ON NONSTATIONARY CHARACTERISTICS OF HYDRAULIC TURBINES
V. B. Kurzin
We have investigated the effect of water compressibility on the nonstationary characteristics of turbines connected with the ability of the liquid to execute natural hydroacoustic vibrations in the setting of hydroelectric units. We have constructed a model of the setting up of forced hydroacoustic vibrations in the water conduit due to the precession of the vortex core running off the turbine. The conditions for the possibility that low-frequency hydroacoustic natural vibrations will arise have been considered.
Keywords: hydraulic turbine, setting, spiral chamber, compressibility, forced natural hydroacoustic vibrations.
MELTING EFFECT ON STEADY LAMINAR FLOW OF A MICROPOLAR FLUID OVER A STAGNATION POINT ON A VERTICAL SURFACE
A. Rasekh,a D. D. Ganji,b S. Tavakoli,b and S. Naeejeec
UDC 536.25 Steady laminar fl ow of a micropolar fl uid towards a stagnation point on a vertical melting surface is investigated. The external velocity is normal to the wall, and the wall temperature is assumed to vary linearly with distance from the stagnation point. The transformed nonlinear ordinary differential equations describing the fl ow are solved numerically by a cubic spline collocation method. The skin friction coeffi cient, local Nusselt number, as well as the velocity and temperature profi les for different values of the governing parameters, are presented. The effects of the melting and material parameters on the fl ow and heat transfer characteristics are examined thoroughly. The results show that both the material and melting parameters reduce the heat transfer rate on the fl uid–solid interface.
Keywords: melting effect, micropolar fl uid, stagnation fl ow, Nusselt number, skin friction coeffi cient, vertical surface.
KINETIC THEORY OF TRANSFER PROCESSES
MULTICOMPONENT SEPARATION POTENTIAL. ELEMENTARY KINETIC THEORY
O. E. Aleksandrov and V. M. Gadel'shin
A molecular model of a multicomponent separation process has been constructed. A general expression for the multicomponent separation potential (value function) has been derived from fi rst principles. The general expression is not tied to a concrete cascade scheme and coincides with the classical expression for the case of a binary mixture. A peculiarity of the separation process, which leads to an infi nite value of the potential for pure components of the mixture, has been revealed.
Keywords: multicomponent separation potential, kinetic theory, isotope separation.
THERMAL DIFFUSION IN BINARY MIXTURES OF MODERATELY DENSE GASES
A. F. Bogatyrev, V. R. Belalov, and M. A. Nezovitina
The thermodiffusion separation of six pairs of gases was measured depending on their pressure and concentration at different temperatures by the two-fl ask method. A comparison of the experimental results with the results of calculations performed using the dimer theory and the thermodynamics of irreversible processes has revealed qualitative and quantitative differences between the experimental and theoretical data. It is shown that the data of calculations performed by the formula obtained within the framework of the elementary kinetic theory agree with the corresponding experimental data within the experimental error.
Keywords: gas mixture, thermal diffusion, experiment, thermal-diffusion constant, molecular-kinetic theory.
MECHANISM OF CHANGE IN THE PHYSICOMECHANICAL PROPERTIES OF POLYIMIDE COMPOSITE FILMS AS A FUNCTION OF THE CONCENTRATION OF AN YBa2Cu3O6+x FILLER
F. F. Komarov,a A. D. Muradov,b A. I. Kupchishin,c and A. V. Leont'eva
A study has been made of the physicomechanical and structural properties of polyimide composite fi lms as functions of the concentration of a YBa2Cu3O6+x fi ller in the range 0.05–0.5 wt.%. A strong infl uence of the concentration of the fi ller on the elastic, plastic, and strength properties of the polymer matrix has been shown. A phenomenological model has been proposed that explains the change in the physicomechanical properties of the composite and is based on a four-layer structural scheme.
Keywords: polyimide composite fi lms, fi ller, polymer matrix, phenomenological model.
EVALUATING THE NATURE OF THE PRESSURE DISTRIBUTION IN A POWDER IN ELECTRIC-IMPULSE SINTERING UNDER CONDITIONS OF UNIAXIAL TWO-SIDED ELASTIC PREPRESSING
O. O. Kuznechik,a D. V. Min’ko,b K. E. Belyavin,b and E. G. Grigor'evc
We have substantiated the phenomenological model of pressure distribution in a powder in the process of electricimpulse sintering taking place under conditions of uniaxial two-sided elastic moulding called prepressing. We recommend using the developed procedure of modeling in calculations related to the optimization of the regimes of electric-impulse sintering that ensure obtaining permeable powder materials with a relatively uniform porous structure.
Keywords: electric-impulse sintering, uniaxial two-sided elastic prepressing.
EFFECT EXERTED BY A RADIO WAVE ELECTROMAGNETIC FIELD ON THE RHEOLOGICAL PROPERTIES OF WATER AND PORTLAND-CEMENT SYSTEMS
V. V. Azharonok,a N. Kh. Belous,b S. P. Rodtsevich,b V. D. Koshevar,b V.G. Shkadretsova,a S. V. Goncharik,a N. I. Chubrik,a and A. I. Orlovichc
We have studied the effect of the regimes of high-frequency (radio wave) electromagnetic treatment of gauging water on the process of structurization and on the technological characteristics of portland-cement systems. It has been established that the radio wave electromagnetic activation of water leads to a reduction in its surface tension, dynamic viscosity, and shear stress, as well as intensifi es the formation of coagulation structures in a portlandcement slurry and aids in increasing the mobility of cement-sand mixtures.
Keywords: gauging liquid, portland-cement slurry, concretes, structurization process, high-frequency electromagnetic fi eld, fi eld effect, shear stress, shear rate, dynamic viscosity, yield point, mobility, placeability, surface tension.