Volume 92, №1
ON THE MECHANISM OF COMBUSTION OF THIN NANOSTRUCTURIZED SILICON PLATES IN OXYGEN AT AN ELEVATED PRESSURE
The physical mechanism of combustion of thin nanostructurized silicon plates in oxygen at an elevated pressure is considered. Based on the analysis of experimental data, it has been established that in combustion wave propagation over a nanostructurized silicon fi lm, the liquid silicon droplets resulting from thermochemical destruction of etched silicon undergo combustion, and that the dominant process is the process of heterogeneous combustion of a gas suspension of silicon particles in oxygen. A physicochemical model is presented that describes the speed of combustion wave front propagation in a gas suspension of silicon particles in a liquid phase depending of the oxygen pressure and silicon particle diameter. Dependences of the combustion front speed and of the time of particle combustion on oxygen pressure and size of particles in a gas suspension have been calculated. It has been established that combustion of silicon particles follows the kinetic mechanism with inverse dependence of combustion time on pressure and its proportional dependence on the particle diameter. The dependence of the degree of fragmentation of particles in the combustion wave front on the structure of a nanostructurized sample and oxygen pressure has been calculated. Practically important recommendations for obtaining higher rates of combustion of nanostructurized silicon fi lms at a lower oxygen pressure have been formulated.
Author: S. I. Futko, I. A. Koznacheev, O. S. Rabinovich, O. G. Penyazkov, and P. N. Krivosheyev
Keywords: silicon, combustion of silicon, nanoporous silicon, thin fi lm, nanostructurized silicon plate, nanomaterials, solid composite fuel, heterogeneous combustion, combustion rate, combustion of a gas suspension of particles, time of particle combustion, kinetic regime of combustion, combustion of solid fuels, structure of solid fuel, two-phase mixture, mathematical simulation, elevated pressure, oxygen
PHYSICOMECHANICAL CHARACTERISTICS OF CONCRETE MODIFIED BY A NANOSTRUCTURED-CARBON-BASED PLASTICIZING ADMIXTURE
The concentration of a nanostructured-carbon-based plasticizing admixture in a concrete mix has been determined, which is optimum for ensuring required technological properties of the mix and physicomechanical characteristics of the concrete. It has been shown that adding this admixture to the concrete mix makes it possible to substantially improve the operating characteristics and longevity of the concrete
Author: S. A. Zhdanok, E. N. Polonina, S. N. Leonovich, B. M. Khroustalev, and E. A. Koleda
Keywords: concrete, plasticizing admixture, nanostructured carbon, placeability, strength characteristics
DETERMINATION OF THE PROTEIN LAYER THICKNESS ON THE SURFACE OF POLYDISPERSE NANOPARTICLES FROM THE DISTRIBUTION OF THEIR CONCENTRATION ALONG A MEASURING CHANNEL
Detection of biomarkers in picomolar or subpicomolar concentrations for revealing marker proteins at the early stage of neurodegenerative diseases is an urgent problem. One of the stages of its solution is determination of the marker’s protein layer thickness adhering to the surface of magnetized nanoparticles. In this work, we present an algorithm for determining the protein layer thickness on the surface of magnetized polydisperse nanoparticles having logarithmically normal size distribution of the magnetic core, as well as the results of the analysis of the error in the determination of the thickness of this layer. The analysis is based on an analytical solution of the equation of diffusion of nanoparticles. With the aid of this solution, in the computational experiment the concentration profi les along the length of the measuring channel have been imitated at the given values of the ″measurement″ duration, protein layer thickness on the nanoparticles surface, and of the relative accidental error of ″measurements.″ It is shown that at the protein layer thickness above 10 nm the proposed technique allows one to determine this thickness with a relative error 5–10 times lower than the error of measuring their concentration
Author: A. Makhaniok, V. A. Goranov, and V. A. Dediu
Keywords: diffusion, concentration, nanoparticles, protein layer thickness, measurement error
INTENSIFICATION OF MATHEMATICAL MODELS OF THE HEAT EXCHANGE IN SPACE VEHICLES
We have investigated the problem of identifying mathematical heat exchange models with lumped parameters for the computing-experimental method for thermal trial of space vehicles on the ground. We have developed a modifi ed variational method of iteration regularization of the solution of identifi cation problems and a combined method for determining the regularization parameter on the basis of minimizing the smoothing functional and the functional-residual of temperature for solving nonlinear problems. The mathematical models of individual systems of thermoregulation of space vehicles have been identifi ed.
Author: A. G. Vikulov and A. V. Nenarokomov
Keywords: mathematical modeling, heat exchange, identifi cation, iteration regularization, variational method, space vehicles
INTEGRAL TRANSFORMATIONS FOR THE GENERALIZED NONSTATIONARY HEAT CONDUCTION EQUATION IN A LIMITED REGION
The mathematical theory of integral transformations has been developed for fi nding analytical solutions of the generalized nonstationary heat conduction equation for a limited canonical-type region (infi nite plate, solid cylinder, sphere) simultaneously in the Cartesian, cylindrical, and spherical coordinate systems. Improved solutions in the form of Fourier–Hankel′s series are suggested that absolutely and uniformly converge up to the boundary of the region and represent fundamentally new constructions of the analytical theory of thermal conductivity of solid bodies very convenient for conducting numerical experiments in the practical thermal physics. The Green′s function method has been developed: an integral relation is suggested for writing analytical solutions of boundary-value problems for the generalized equation of nonstationary heat conduction in terms of inhomogeneities in the equation and boundary-value conditions in the initial formulation of the problem, and the corresponding Green′s functions are presented
Author: É. M. Kartashov
Keywords: generalized equation of nonstationary heat conduction, limited regions, integral transformations, Fourier–Hankel series, Green′s function method
HEAT TRANSFER IN A HALF-SPACE WITH TRANSVERSAL ANISOTROPY UNDER THE ACTION OF A LUMPED HEAT SOURCE
The authors have obtained a novel analytical solution to the problem of the theory of heat conduction in an anisotropic half-space with an anisotropy of the transversal type when the anisotropy takes place in planes formed by two coordinate axes, whereas in the direction of the third coordinate axis guided deep into the body, the material is isotropic. The solution was obtained by two applications of the variablewise Fourier transformation in the anisotropy plane and of the specially developed method of substitution in the direction of the third coordinate. The obtained results point to the drift of the heat fl uxes and temperature fi elds toward the principal axis with a larger coeffi cient of the thermal-conductivity tensor, with this coeffi cient being the larger the higher the degree of anisotropy in the indicated direction. It has been established that isothermal surfaces have the shapes of elliptic paraboloids.
Author: V. F. Formalev and S. A. Kolesnik
Keywords: thermal-conductivity tensor, transversally anisotropic body, nonstationary temperature fi eld, analytical solution, degree of anisotropy, curvature of the temperature fi eld
EFFECT OF HEAT FLOW ON THE STRESSED STATE OF A THREE-LAYER ROD
This paper considers the change in the stressed state of a three-layer elastoplastic rod with a compressible fi ller in a heat fl ow. The temperature change was calculated with the help of the formula obtained by averaging the thermal properties of the materials of the layers over the rod thickness. To describe kinematically the thickness asymmetric stack, broken line hypotheses were assumed: in thin bearing layers Bernoulli hypotheses hold; in the thin thickness-compressible fi ller the Timoshenko hypothesis with a linear approximation of displacements in the layer thickness holds. The work of the fi ller in the tangential direction is taken into account. The physical relations between stresses and deformations agree with the theory of small elastic deformations. The system of differential equilibrium equations was obtained by the variational method. At the boundary, kinetic conditions of rest of rod ends on rigid supports fi xed in the space are assumed. The solution of the boundary-value problem was reduced to the obtaining of four sought functions — bendings and longitudinal displacements of median surfaces of the bearing layers. The analytical solution was obtained by the method of elastic solutions in the case of uniformly distributed continuous and local loadings. Its numerical analysis has been carried out. The change in stresses on the outer planes of the rod layers and in the cross section in the middle of the rod under the action of the heat fl ow has been investigated.
Author: É. I. Starovoitov and L. V. Leonenko
Keywords: three-layer rod, stressed state, plasticity, compressible filler, heat flow.
CFD MODELING OF OPERATING PROCESSES OF A SOLAR AIR HEATER IN ANSYS FLUENT
Rapid development of the technologies of use of renewable energy sources in the recent decade has opened up prospects for satisfying our society′s ever growing needs for fuel and power resources. In the present work, the author has shown results of investigation into the thermal and aerodynamic characteristics of a solar air heater. A computer model whose adequacy has been confi rmed using experimental data was developed in the ANSYS Fluent software product. It has been determined that for the end of calendar autumn, the operating effi ciency of the solar air heater is the highest at the angle of inclination of the absorption surface to the earth α = 60o . The dependence of the value of heating of air in the solar heater during daylight hours has been determined in the physical and computer experiment; it has been established that for the city of Samara (GMT + 4) the maximum air heating is observed in the interval between 13.00 and 14.00. The infl uence of transverse ribs on the heat exchange between the light-absorbing surface and the air has been shown. A curvilinear shape of the temperature contour is formed in the immediate vicinity of the ribs due to the formation of vortices and reverse-current zones.
Author: D. I. Pashchenko
Keywords: ANSYS, CFD modeling, renewable energy sources, solar air heater, energy efficiency
POTENTIAL OF COCONUT OIL FOR TEMPERATURE REGULATION IN TROPICAL HOUSES
The use of a thermal mass is a well-known technology for conditioning the indoor thermal environment in tropical houses. Architects and builders generally used heavy-weight building materials, such as concrete and bricks, for walls and fl oors to ensure thermal comfort of rooms; however, it is diffi cult to make a good composition of thermal masses that can result in thermally comfortable conditions. This paper discusses the potential of coconut oils (co_oil) as an indoor thermal energy storage (TES) material for improving the thermal performance of rooms in addition to the existing thermal masses used in tropical houses in Bandung, Indonesia. Co_oil is a very promising organic phase-change material (PCM) due to its high thermal capacity storage in sensible and latent phases. In this paper, the application of co_oil for temperature regulation is considered in the light of two important aspects, such as the use of addition of a co_oil mass and the effect of room air circulation. The role of PCM in the form of co_oil as a TES material to regulate indoor air temperature is reported.
Author: S. Wonorahardjo, I. M. Sutjahja, and D. Kurnia
Keywords: temperature regulation, thermal energy storage, coconut oil, building component.
DEVELOPMENT OF ELEMENTS OF REUSABLE HEAT SHIELDS FROM A CARBON–CERAMIC COMPOSITE MATERIAL 1. THEORETICAL FORECAST
For the new generation of space vehicles with a reusable heat shield, it is promising to use carbon-ceramic composite materials resistant to powerful heat fl ows arising by the descent of such a vehicle in the atmosphere. This paper presents the results of the theoretical forecast of characteristics of a heat shield from a porous carbon–ceramic composite made on the basis of testing specimens of this composite on a gas-dynamic stand simulating real operating conditions of the heat shield. Methods have been developed for simulating the heating and ablation of specimens of carbon–ceramic composites under their convective heating in a plasmatron. It has been established that the diameter of the nozzle of the gas-discharge channel of the plasmatron and its distance to the frontal surface of the specimen infl uence the temperature regime of tests. We propose an experimental procedure for attaining a temperature of 273 K on the frontal surface of a cylindrical specimen of a carbon–ceramic composite material of diameter 70 mm and height 70 mm.
Author: S. V. Reznik, P. V. Prosuntsov, and K. V. Mikhailovskii
Keywords: reusable heat shield, composite porous carbon–ceramic material, thermal tests, gas-dynamic stand, convective heating
ESTIMATION OF ELECTROKINETIC PARAMETERS FOR ROCKS IN SINGLE-PHASE AND TWO-PHASE FLOW EXPERIMENTS
The authors has conducted experiments on estimation of electrokinetic parameters of porous permeable rocks using sandstone samples have been conducted in the regimes of stationary single-phase fl ow of an aqueous electrolyte solution and stationary two-phase fl ow of a water/ kerosene mixture in a 50:50 ratio. The values of the ζ potential of the electric double layer and also of the coeffi cients of streaming potential and electroosmosis have been estimated. The results, on the whole, are in agreement with the known estimates obtained by traditional methods. In the two-phase fl ow experiments, a monotonic reduction in the electrokinetic parameters with growth in the pressure gradient was recorded on a model with the change of sign of the charge. This effect is attributed to the specifi c adsorption of potential-forming ions and, probably, to the partial hydrophobization of the surface of the mineral phase.
Author: V. L. Barabanov
Keywords: rocks, electrokinetics, streaming potential, single-phase fl ow, two-phase fl ow, electric double layer, ζ potential, laboratory experiments
ANOMALOUS NONISOTHERMAL TRANSFER OF A SUBSTANCE IN AN INHOMOGENEOUS POROUS MEDIUM
Consideration has been given to nonisothermal anomalous transfer of a substance in an inhomogeneous porous medium consisting of two parts with different porosity and permeability properties and characteristics of transfer of the substance. In contrast to the approaches that are used in the theory of interpenetrating continua for the problems of fi ltration and transfer of a substance and heat, here the authors consider one medium; the transfer of a substance and heat to the other medium in relevant equations is only taken account of by the source (sink) term in the form of a fractional time derivative of the concentration of the substance and the temperature. Account for the dependence of the diffusion coeffi cient of the substance on temperature leads to coupled systems of equations for the concentration of the substance and the temperature, which are solved numerically
Author: B. Kh. Khuzhayorov, T. O. Djiyanov, and T. R. Yuldashev
Keywords: anomalous transfer, anomalous heat transfer, fractional derivatives, concentration of the substance, temperature, numerical solution
SIMULATION OF HEAT AND MASS TRANSFER IN ADSORPTION OF GAS MIXTURES IN A TRANSITION REGIME
The problems of simulating heat and mass transfer of the process of adsorption in a stationary adsorbent layer are considered. At elevated concentrations of gaseous mixtures, the thermal effect exerts a substantial infl uence on the progress of the adsorption process and requires it to be taken into account. The adsorption heat, while increasing the internal temperature of the adsorbent and adsorptive layer, exerts a negative effect on the absorption of undesirable gaseous mixture components. Attainment of the rate of equilibrium state in heat and mass transfer processes is very important in determining the effi ciency of operation of adsorption apparatuses. In the case of nonisothermal adsorption, it is very important to be able to predict the behavior of the stationary adsorbent layer temperature in time, because it turns out to be most advantageous economically to carry out abstraction of the product from an industrial adsorber prior to the establishment of equilibrium state, i.e., in a transition regime. A mathematical description of heat transfer of industrial adsorbers has been obtained. A mathematical model has been developed allowing one to determine the temperature in a stationary adsorbent layer at each instant of time (using as an example the process of adsorption refi ning of gaseous mixtures CO2, H2S, NO2 on NaX zeolite). To model heat and mass transfer, the heat conduction equation is used, i.e., a differential equation of parabolic type. Heat and mass transfer was investigated for each moment in a stationary layer, and heat and mass transfer between the gaseous fl ow and the stationary layer of NaX zeolite has been determined.
Author: F. V. Yusubov and A. S. Bairamova
Keywords: heat and mass transfer, adsorber, zeolite, gaseous mixtures, simulation
HEAT AND MASS TRANSFER IN MHD POISEUILLE FLOW WITH POROUS WALLS
An exact solution of the problem of a steady MHD Poiseuille fl ow with heat and mass transfer in the presence of a transverse magnetic fi eld has been obtained with consideration for the induced magnetic fi eld and thermal diffusion. The walls are assumed to be isothermal, porous, and subjected to suction/injection at a constant velocity. The effects of the Hartmann number and the magnetic Reynolds number on the velocity, temperature, and concentration fi elds, as well as on the volumetric and magnetic fl uxes per unit width across the normal section of the channel and on the current density are studied. The present analysis includes also the effect of the Soret number on the transport characteristics. The novelty of the analysis is that the viscous and magnetic Reynolds numbers are unrestricted.
Author: N. Ahmed
Keywords: current density, magnetic fl ux, volumetric fl ux, pressure gradient, isothermal wall, induced magnetic field
CONJUGATE PROBLEM ON NONSTATIONARY HEAT EXCHANGE IN SUPERSONIC FLOW OVER A BLUNT-NOSED CONE
A conjugate problem on the nonstationary heat exchange in the supersonic gas fl ow past a conic body with a nose blunted over a sphere at a zero angle of attack was solved for the case where the stagnation fl ow temperature is as high as 2500 K. The possibility of control of the temperature regime of such a body in the case where a laminar fl ow is realized in the boundary layer on its surface was investigated. The results of calculations were generalized in the form of criterion dependences allowing one to determined the maximum temperature on the surface of the body with a good accuracy, including for a nonstationary fl ow over it, which makes it possible to estimate the ranges of thermophysical and geometric parameters of the body in which the temperature of its surface can be decreased to a required level.
Author: V. I. Zinchenko and V. D. Goldin
Keywords: aerodynamic heating, heat exchange, heat-insulating material, laminar boundary layer
INTERACTION OF SOLID PARTICLES WITH VORTEX STRUCTURES AND CONCENTRATION DISTRIBUTION OF SUCH PARTICLES IN A COMBINED VORTEX
The interaction of solid particles with vortex structures was investigated, and the scattering of such particles by a combined vortex was numerically simulated using the Euler–Lagrange approach. The concentration distributions of particles in the region of a gas fl ow occupied by a vortex at different instants of time have been obtained. The dependence of the time for which these particles escape from the central zone of the vortex on their size was determined. The results obtained can be used for increasing the effi ciency of measurement of the parameters of the disperse phase in a fl uid fl ow by optical methods.
Author: K. N. Volkov, V. N. Emel′yanov, and I. V. Teterina
Keywords: numerical simulation, vortex, particle, concentration, optical method.
SIMULATION OF THE FLOW OF A GASEOUS HYDROCARBON COMPOUND AND ITS THERMODESTRUCTION IN A HEAT-LOADED CHANNEL OF LARGE LENGTH
A two-dimensional mathematical model is proposed for calculating the parameters of a nonequilibrium fl ow of a gaseous hydrocarbon compound in a heat-loaded cylindrical channel of large length on the basis of the system of Navier–Stokes equations for a multicomponent mixture of heat-conducting viscous gases with a reduced mechanism of chemical kinetics. On the basis of processing of the results of calculations by this model, an integral one-dimensional mathematical model of a viscous fl ow of a gaseous hydrocarbon compound decomposed in an endothermic gross reaction, allowing one to perform a large number of computer calculations for a minimum time, has been developed. The results of calculations of the nonequilibrium fl ow of a gaseous hydrocarbon compound in a channel of large length by these models were compared with experimental data. Results of a parametric investigation of the cooling of channels having a large length by gaseous hydrocarbons in different regimes of their fl ow in them and at different heat loads on the channel walls are presented. The mathematical models developed and the data obtained with them can be used for estimating the effi ciency of cooling of the channels of process installations and power plants by gaseous hydrocarbon compounds.
Author: K. Yu. Aref′ev, K. V. Fedotova, L. S. Yanovski V. Yu. Aleksandrov, and P. D. Toktalieva
Keywords: hydrocarbon compound, decomposition, gross reaction, reduced mechanism, chemical kinetics, channel of large length
AN INVERSE PROBLEM OF ACOUSTIC FLOW
A one-dimensional mathematical model is suggested for nonstationary incompressible fl ow in a cylindrical tube under the action of a sonic wave propagating in it. Within the framework of this model, a problem of determining the acoustic energy density at the beginning of the tube from the given volumetric fl ow rate of the fl uid in the tube is posed. This problem relates to the class of inverse problems associated with the restoration of the dependence of the right-hand sides of parabolic equations on time. A computational algorithm is proposed for solving the problem posed.
Author: Kh. M. Gamzaev
Keywords: sonic wave, acoustic energy density, radiation pressure gradient, inverse problem
MAGNETOHYDRODYNAMICS AND HEAT TRANSFER IN ROTATING FLOWS
The motion of a viscous conducting medium caused by the rotation of an extended dielectric disk in an axial magnetic fi eld in the presence of an axial temperature gradient is considered. For the case of a strong magnetic fi eld, the values of the Nusselt number on the disk surface are estimated. A comparison of the obtained results with the well-known data of numerical calculation is made. Based on the calculated profi le of the azimuthal velocity of the medium in the boundary layer on the disk, the motion of liquid is investigated in the space between two dielectric disks rotating in the same direction with different angular velocities in the presence of suction and blowing through their solid porous surfaces. The results of calculation of the angular rotational velocities of an inviscid core depending on the suction and magnetic fi eld parameters are given.
Author: V. D. Borisevich and E. P. Potanin
Keywords: rotating disk, heat transfer, magnetic fi eld, suction, boundary layer, conducting gas
INTERACTION OF A WATER MEDIUM AND A SOLID COMPOSITE GAS-PRODUCING FORMULATION BASED ON BUTYL RUBBER
The authors have given experimental data on the change in the mass of a cylindrical specimen of a solid composite gas-producing formulation based on butyl rubber and ammonium perchlorate as a function of the holding time in seawater. The depth of surface washout of the oxidant has been assessed for these conditions. Consideration has been given to the questions of reduction of the gas-producing power of relevant full-scale blocks as applied to their possible use for blowing of deep-sea ship-raising pontoons depending on the residence time in the water medium, which is determined by the period of preparatory work.
Author: V. D. Barsukov, S. V. Goldaev, N. P. Min′kova, and L. A. Savel′eva
Keywords: composite gas-producing formulation, butyl rubber, ammonium perchlorate, water medium, oxidant, washout depth, gas-producing block, ship-raising pontoon
SIMULATION OF THE CONVECTIVE HEAT EXCHANGE IN THE SPHERICAL LAYER OF AN ELECTRICALLY CONDUCTING LIQUID
Results of numerical simulation of the convective heat exchange in the electrically conducting liquid fl owing in the space between two concentric isothermal spheres are presented. The infl uence of the Joule heat dissipation, the electromagnetic forces, and the Grashof number on the structure of the liquid fl ow, its temperature and magneticinduction fi elds, and the distribution of Nusselt numbers in it was investigated.
Author: S. V. Solov′ev
Keywords: mathematical simulation, convective heat exchange, Joule heat dissipation, magnetic hydrodynamics, spherical layer
HYPERBOLIC MODEL OF A ONE-VELOCITY VISCOUS HEAT-CONDUCTING MEDIUM
A modifi ed, generalized-equilibrium model of a one-velocity heterogeneous medium is presented, which accounts for the viscosity and thermal conductivity of the mixture, as well as for interfractional heat transfer. A characteristic analysis of the model′s equations has been carried out, and their hyperbolicity is shown. A description is given of Godunov′s method with a linearized Riemann solver intended for calculating mixture fl ows on curvilinear grids, with the use of which a number of problems for a vapor–air mixture has been investigated.
Author: V. S. Surov
Keywords: hyperbolic model of a viscous heat conducting mixture, interfractional heat transfer, Godunov′s method, linearized Riemann solver
MATHEMATICAL MODELING OF SWIRLING HERSCHEL–BULKLEY PSEUDOPLASTIC FLUID FLOW IN A CYLINDRICAL CHANNEL
Results of investigations into the swirling fl ow of a pseudoplastic fl uid with a Herschel–Bulkley yield stress in a cylindrical channel have been presented. It has been established that a growth in the rates of shear strains in fl ows with a swirl causes the values of effective viscosity to decrease. It has been shown that at one and the same Rossby number, the recirculation strength is the greater the smaller the values of the limiting shear stress, the consistency, and the nonlinearity index.
Author: O. V. Matvienko, V. P. Bazuev, and A. E. Aseeva
Keywords: rheology, pseudoplastic media, viscoplastic fl uid, Herschel–Bulkley fl uid, swirling fl ows, computational hydrodynamics
COMPUTATIONAL AND EXPERIMENTAL INVESTIGATIONS OF THE WORKING PROCESS IN A RECOVERY BURNER
The authors have presented computational and experimental investigations into the burning of sulfur-containing oil gases of heterogeneous composition and calorifi c power in a burner whose combustion products are the working medium for the recovery-power-plant′s turbine drive. The equations of the working process have been written in the context of a generalized law of conservation. The results of numerical modeling have been obtained with the ANSYS FLUENT software package. The experimental data have been derived during the burning of the oil gas stored in cylinders directly at a marginal fi eld. A comparison of the calculated and experimental data has shown the adequacy of the computational model. The calculation results allow the conclusion on the correctness of the technical decisions adopted earlier on creation of a domestic recovery gas-turbine plant of the blocked-module type for marginal fi elds.
Author: N. L. Bachev, O. O. Matyunin, O. A. Betinskaya, N. Yu. Bacheva, and R. V. Bul′bovich
Keywords: mathematical model, equations of the working process, boundary conditions, generalized law of conservation, comparison of theoretical and experimental data, sulfur-containing gas, casing-head oil gas.
IGNITION OF HOVERING DROPLETS OF ORGANIC COAL WATER FUELS
An experimental study has been made of the ignition of droplets of organic coal water fuels prepared from moist waste (obtained by the fl otation technique) of coal washing and used industrial oils with the use of a high-speed system of video recording of the processes proceeding in a model combustion chamber. A comparison has been made between the ignition inertias characteristics of a single droplet of organic coal water fuels, a group of three droplets, as well as of a polydisperse fl ow of a slurry fuel. All experiments were performed for hovering droplets (upon dehydration of the surface layer they are considered as particles) of organic coal water fuels in a model combustion chamber fi lled with heated air (the temperature was from 800 to 900 K). The established differences between the ignition characteristics of the slurry fuels in the three investigated schemes illustrate the possibility of prognostic evaluation of ignition characteristics of droplet aerosols of organic coal water fuels with the example of a single droplet. We present the dependences of ignition characteristics of single hovering droplets of organic coal water fuels of various component compositions on the group of diagnostic variables (temperature and fl ow velocity of the oxidizer, initial sizes of droplets, and concentration of the component composition). The prospects of using the obtained experimental results to optimize the performance of power-generating plants are shown.
Author: T. R. Valiullin, K. Yu. Vershinina, V. V. Medvedev, and I. P. Ozerova
Keywords: organic coal water fuels, single droplet, polydisperse fl ow, hovering, ignition
MODIFIED CONSTANT OF COMBUSTION OF POROUS COAL PARTICLES
Time dependences of the diameter and density of burning single porous coal particles have been investigated. Using as an example a coke particle of the Nazarovsk coal, it is shown that in the course of combustion of such a particle the product of its density by the square of its diameter decreases linearly. A new combustion constant of coal is suggested. An analytical substantiation of the empirical dependence of the time of combustion of coal coke particles on their initial dimensions and densities, oxygen content in them, and on the gaseous mixture temperature has been carried out.
Author: V. V. Kalinchak, A. S. Chernenko, and M. N. Korchagina
Keywords: combustion, arbitrary extinction, porosity, coal particle, reactivity index.
CONDITIONS AND CHARACTERISTICS OF HIGH-TEMPERATURE PROCESSES OF EBULLITION AND DISINTEGRATION OF DROPLETS OF WATER EMULSIONS
Experimental investigations into the high-temperature (700 to 1200 K) heating, evaporation, ebullition, and subsequent disintegration (breakup) of droplets of water emulsions (with a volume concentration of petroleum products to 70%) have been performed using high-speed video recording. Consideration has been given to the emulsions based on water, oil, mazut, kerosene, and industrial oil. A study has been made of two schemes of supply of energy to the droplet: local heating due to the contact with a heated metallic rod with variation in the cross section of its tip and evaporation on a massive heated substrate, i.e., a steel platelet of diameter 50 mm and thickness 5 mm. From the results of an analysis of the frames of videograms illustrating different schemes of implementation of the investigated processes of transformation of the surface of the emulsion droplet and of its heating, evaporation, fi lling with vapor bubbles, ebullition, and breakup, the authors have established the infl uence of basic factors (temperature and surface area of heating, concentration of the components, droplet dimensions, and properties of petroleum products) on the time of full evaporation of the emulsion droplet. Distinctive features of the processes of evaporation and ebullition of emulsion droplets in high-temperature superheating have been determined. The authors have singled out different regimes of heating of the droplets, which differ not only by the time of full evaporation but also by the effects (preservation of a monolithic state, explosive disintegration accompanied by the formation of a fi ne aerosol, and ignition of the emulsion).
Author: R. S. Volkov, G. V. Kuznetsov, and P. A. Strizhak
Keywords: emulsion, water, impurities, petroleum products, droplet, evaporation, boiling, disintegration, hightemperature heating, rod, substrate
MATHEMATICAL SIMULATION OF CONVECTIVE DIFFUSION IN AN ENERGY-SAVING MODE OF DEGASSING OF A METAL MELT BY A COMPLEX ACTION
On the basis of the developed model, the authors have made a numerical analysis of the convective diffusion of hydrogen in a liquid bath (degree of its degassing) as a function of the technological parameters of the process. It has been established that the effi ciency of the diffusion processes decreases with increase in the diameter of the purger pores and in the pressure in a vacuum chamber, and increases with liquid-bath depth and blowing rate, but to a certain level, after which the process′s effi ciency ceases to grow. It has been shown that the reduction in the rate of blowing to an optimum level saves expensive argon
Author: N. I. Zakharov and I. V. Tupilko
Keywords: convective diffusion, mathematical model, liquid bath, hydrogen, rate of blowing, vacuum chamber, energy saving
TECHNOLOGY OF ELECTRIC MELTING OF BASALT FOR OBTAINING MINERAL FIBER
The basalt electric melting advantages in application of basalt fi ber in industrialized construction and heat power engineering are shown. The results of thermodynamic calculations of the process of Kazakhstan basalt melting are given. The calculations have shown that in gaseous and condensed products of the process there are no harmful substances. Experiments on electric melting of basalt in a reactor with electromagnetic mixing of the melt were carried out. The prospects of electric melting of basalt and obtaining mineral fi ber with the use of small-size module installations involving an electromagnetic reactor are shown. The specifi c energy consumption for obtaining a homogeneous basalt melt does not exceed 1.1 kW·h/kg, which is superior to the widely used SHF-reactors in which the specifi c energy consumption is several times higher
Author: V. G. Luk′yashchenko, V. E. Messerle, A. B. Ustimenko, V. N. Shevchenko, S. Kh. Aknazarov, Z. A. Mansurov, and K. A. Umbetkaliev
Keywords: basalt, electromagnetic reactor, electric melting, specifi c energy consumption, gas-dynamical installation, centrifuge, mineral fiber
RELATIONSHIP BETWEEN THE THERMAL CONDUCTIVITY AND VISCOELASTIC PROPERTIES OF POLYVINYLCHLORIDE FILLED WITH NANODISPERSED METAL
The authors have given results of an investigation of the thermal conductivity and viscoelastic properties of metalnanodispersed systems based on polyvinylchloride at 298 ≤ T ≤ Tg + 10 K which contains 0 ≤ φ ≤ 1.0 vol.% Cu and NiCr. Using the Alfrey–Maxwell model, an analytical correlation has been established between the properties of the composite in ultrasonic and thermal fi elds and the ways for their directional control have been pointed
Author: B. B. Kolupaev and B. S. Kolupaev
Keywords: polyvinylchloride, dissipation, structural element, quasi-equilibrium, irreversibility criterion
CALCULATION OF GAS FLOW BETWEEN TWO COAXIAL CYLINDERS IN A FREE-MOLECULAR REGIME UNDER SPECULAR-DIFFUSE BOUNDARY CONDITIONS
Using the method of characteristics, within the framework of the kinetic approach, an analytical solution of the problem on gas heat and mass transfer in a long channel formed by two coaxial cylinders in a free-molecular regime has been constructed. As the basic equation describing the kinetics of the process, use is made of the Boltzmann kinetic equation for a collisionless gas and as a boundary condition of the channel walls — a model of speculardiffuse refl ection. The profi le of the heat fl ux vector in the channel has been constructed, and the gas heat and mass fl ows through the channel cross section have been calculated as functions of the accommodation coeffi cients of the gas molecule pulses tangent to the surfaces of the cylinders
Author: O. V. Germider, V. N. Popov,and A. A. Yushkanov
Keywords: coaxial cylinders, gas fl ow, free-molecular regime, specular-diffuse boundary conditions.