Volume 93, №4
ON REALIZATION OF IDEAL MULTIFLOW HEAT EXCHANGE
It is shown that the conditions of ideal heat exchange, according to which at the given heat load and overall heat transfer coeffi cient the entropy production in the system attains its lower boundary, can be realized in a set of countercurrent heat exchangers on coordinated selection of temperatures and heat capacities of fl ows. The parameters of fl ows and the distribution of heat transfer coeffi cients and heat loads between two-fl ow heat exchangers for the Newtonian kinetics have been determined. The value of the minimal dissipation and the profi le of the distribution of the overall heat transfer coeffi cient for the case where the temperature profi le of one of the fl ows is fi xed have been obtained.
Author: A. M. Tsirlin
Keywords: ideal heat exchange, heat transfer coeffi cient, entropy, heat loads, Newtonian kinetics
ON THE THERMAL REGIME OF THE PROTECTIVE GRANULAR BED OF A GAS DISTRIBUTOR
A numerical solution of a two-temperature problem on the thermal state of an aerated granular bed, constituting the thermal protection of the gas distributor of a high-temperature bubbling bed, is carried out. An equation is obtained for the coeffi cient of the effi ciency of cooling the gas distributor. It is shown that on the side of the bubbling bed the surface temperature of the granular bed is independent of its thermal conductivity and thickness
Author: Yu. S. Teplitskii, E. A. Pitsukha, and A. R. Roslik
Keywords: bubbling bed, thermal protection, granular bed, gas distributor, cooling effi ciency
HEAT AND MOISTURE TRANSFER IN A STATIONARY DISPERSED LAYER OF VEGETABLE MATERIALS WITH COMBINED POWER INPUT
The results of modeling and investigating heat and moisture transfer in a stationary dispersed layer of vegetable materials with convective and cyclic SHF-convective power input are presented. The mathematical model is made up of equations for conservation of gas-phase mass, fi ltration, and heat and moisture transfer in phases accounting for internal resistance to transfer of heat and moisture in particles in calculating the processes of heat and mass transfer and on the basis of deepening the evaporation zone. The conformity of the calculated results with the experimental data using the example of drying sliced potato particles and the possibility of stepping up the process of dehydration is shown.
Author: P. V. Akulich and D. S. Slizhuk
Keywords: heat and moisture transfer in a stationary layer, drying of vegetable materials, SHF-convective drying
FORMATION OF CRACK ON HYDRAULIC FRACTURING OF BED IN A MEDIUM WITH DOUBLE POROSITY
A study is made of a two-dimensional bound problem on slow motions of a liquid in a hydraulic fracturing crack and on deformations and fi ltration caused by these motions in a poroelastic medium with double porosity involving two components — the porosity proper and jointing. The motions are induced by the pumping of a liquid into a well. The motion inside the crack is described by hydrodynamics equations in hydrostatic approximation. Some ordered sequence of interdependent geomechanical processes occurring on hydraulic fracturing is established in conformity with the principle of incomplete connection. In the main space surrounding the crack, the liquid moves in the porous component of the two-phase medium. In the boundary layer the motion dominates in the jointy component. In distinction to the classical problem with double porosity, the indicated problem is solved rigorously with account for elastic deformations of the skeleton. The motion regimes in the main volume and in the boundary layer differ signifi cantly due to the permeability of the medium
Author: A. V. Karakin
Keywords: jointing, porosity, poroelasticity, double porosity, hydraulic fracturing crack
TURBULENT DRIFT OF FINELY DISPERSED PARTICLES IN EMULSIONS AND SUSPENSIONS IN PRESSURE HYDROCYCLONES
Consideration has been given to a mathematical model of turbulent drift of fi nely dispersed particles in the liquid phase of a hydrocyclone. With the two-layer model of a turbulent boundary layer and the coeffi cient of turbulent diffusion of the particles, the authors have obtained an expression for calculating the coeffi cient of the rate of particle transport from the fl ow core to the boundary of a viscous sublayer on the apparatus wall. On the basis of the expression for shear stress on the wall, which was written with a momentum-transfer coeffi cient, an expression has been obtained for calculating the average circular velocity in the hydrocyclone. The basic parameter of these expressions is the dynamic velocity, which is determined from the average rate of energy dissipation. Results of calculations of the coeffi cient of transport of particles, the average circular velocity, and the effi ciency of separation of particles of diameter 6 μm (sand particles in oil) have been presented; a comparison of the results with experimental data has been made.
Author: A. G. Laptev, M. M. Basharov, and E. A. Lapteva
Keywords: hydrocyclone, turbulent diffusion, transfer coeffi cients, separation effi ciency
APPLICATION OF ELECTROSTATIC EFFECT FOR CLEANSING FINELY DIVIDED AEROSOL FROM AIR
The possibility of intensifying the processes in gas-dispersed systems with coagulated particles of different dimensions and the effi ciency of air purifi cation depend on the characteristics of the fi eld created by electrodepositing plants. This work was carried out with a view of optimizing the parameters of electrodepositing systems to increase the rate of aerosol cloud deposition in an air medium. The theoretical and experimental studies are oriented to improving the methods of removing harmful aerosol formations in the air space by exposure to external electrostatic fi elds. This paper describes experimental investigation of coagulation and deposition of aerosol particles by inducing external fi elds in a closed volume with account for different technical parameters of devices for trapping different kinds of fi nely divided particles. To obtain the dispersed and concentration characteristics of aerosol, use is made of the method of searching for the solution in the form of a multiparameter function of the size distribution of particles realized as part of a laser measuring complex.
Author: M. Yu. Stepkina, O. B. Kudryashova, A. A. Antonnikova, and A. A. Zhirnov
Keywords: finely divided aerosol, drift velocity, deposition, coagulation, critical voltage of corona discharge, multiparameter distribution function
THERMAL STABILITY AND PHASE COMPOSITION OF STRATIFYING POLYMER SOLUTIONS IN SMALL-VOLUME DROPLETS
Within the framework of the thermodynamic approach the characteristic features of the phase equilibria and of thermal stability of liquid polymer solutions in small-volume systems are considered. Using as an example a stratifying solution of oligomer fractions of polybutadiene and polystyrene in coarsely disperse droplets of different volumes with core–shell confi guration, the regions of thermal stability of various heterogeneous states of the core– shell structure that differ by the compositions of core phases and of homogeneous state are obtained . It is shown that these regions of temperatures depend substantially on the droplet volume, with the compositions of the coexisting phases in different states of the core–shell structure being different. A decrease in the droplet volume is accompanied by a substantial change of the mutual solubilities of components, as well as by a decrease of the upper critical temperature of solubility and by the expansion of the temperature region, in which solutions of any composition up to the equimolar one are dynamically stable.
Author: A. V. Shishulin and V. B. Fedoseev
Keywords: disperse systems, dimensional effect, solutions of polymers, phase transformations, solution stratifi cation, metastable states
MODELING IMPREGNATION OF POROUS MATERIALS IN A FORCE FIELD WITH ACCOUNT OF THE DIFFUSION OF TRAPPED GASES
It has been shown that a nonuniform electric fi eld can have a signifi cant effect on the kinetics of diffusion capillary imbibition of liquids into thin dead-end capillaries that are a model of pore strictures. The results of calculations are in satisfactory agreement with experimental data
Author: I. N. Karpovich
Keywords: cylindrical dead-end capillary, liquid column, gas diffusion, nonuniform electric fi eld, mass transfer, porous body
STUDY OF THE MOISTURE SORPTION ISOTHERMS AND ISOSTERIC HEAT OF SORPTION OF THE MEDICINAL PLANT Launeae Nudicaulis FROM ALGERIAN SAHARA
The aim of this work is to determine the sorption isotherms of Launeae nudicaulis, a medicinal plant growing in south-west of Algeria. The equilibrium moisture content was measured, using the static gravimetric method, with the water activity from 6.3 to 89.8% at 30 and 40o C. It was shown that at higher water activities the moisture content increases sharply with the temperature, resulting in crossing of the isotherm curves. Four models were applied for analyzing experimental data (namely, the Peleg, GAB, Henderson–Thompson, and the BET modifi ed ones). The desorption and adsorption data showed the best correlation with the Peleg model. The isosteric sorption heat of water was determined from the equilibrium data at different temperatures. This heat was shown to decrease as the moisture content increases and to be a polynomial function of the moisture content.
Author: A. Fedol, A. Cheriti, and M. R. Ouahranib
Keywords: Launeae nudicaulis, equilibrium moisture content, modeling of sorption isotherm, isosteric heat of sorption
MATHEMATICAL SIMULATION OF THE SWIRLING FLOW OF A THERMOVISCOUS, PSEUDOPLASTIC SISCO FLUID IN A CYLINDRICAL CHANNEL
The swirling fl ow of a thermoviscous, pseudoplastic Sisco fl uid in a cylindrical channel was investigated. It was established that, in the case of irrotational fl ow of a pseudoplastic fl uid in such a channel, the effective viscosity of the fl uid in the neighborhood of the channel axis is substantially increased. A swirling of this fl ow leads to an increase in the rate of shear deformation of the fl uid in the axial region of the fl ow and to a decrease in its effective viscosity. As the swirling of the fl ow in the channel increases, the fl uid near the channel walls and the fl uid at the boundary of the recirculation zone are subjected to a dissipative heating leading to a decrease in their effective viscosity. The intensity heating of the fl uid in the channel increases with increase in the rate of swirling (the Rossby number) of its fl ow.
Author: O. V. Matvienko and A. E. Aseeva
Keywords: rheology, non-Newtonian fl uid, thermoviscous fl uid, pseudoplastic Sisco fl uid, heat exchange, swirling fl ow, viscous dissipation, computational hydrodynamics
EXCLUDED VOLUME IN MICRORHEOLOGICAL MODELS OF STRUCTURED SUSPENSIONS
An exact solution of rheology equations, which is possible for a layered two-phase material simplest of structure, is used as a tool for testing concepts and rheological equations obtained on the basis of the existing structural models of disperse systems and for ranking the models by the extent to which the excluded-volume effect is taken account of in them. Consideration has been given to the features of fl ow of layered systems in which the dispersed phase is a continuous impermeable medium, an elastic material, and a coagulation structure permeable to a dispersion medium. In the context of the model of fl ow of layered systems, the authors interpret the fl ow regime observed experimentally, the so-called "stress plateau," which is characteristic of liquid crystalline structures and polymer melts
Author: E. E. Bibik, E. V. Sivtsov, and V. D. Rodinova
Keywords: rheology, viscosity, free volume, shear, elastoplasticity
ON THE REFRACTIVE INDEX OF A GAS UNDER HIGH-THERMAL-NONEQUILIBRIUM CONDITIONS
An analysis has been made of the infl uence of the excitation of internal degrees of freedom of molecules on the refractive index (n – 1) under the conditions of high thermal nonequilibrium using the problem on relaxation of molecular nitrogen and oxygen behind the front of a strong shock wave as an example. It has been shown that the processes of vibrational relaxation and the processes of electronic translational relaxation and dissociation alike may exert a substantial infl uence on the refractive index of the gas. The change in the refractive index has been shown to occur primarily because of the change in the gas density in the course of these processes. Also, it has been found that a slight but detectable infl uence (about 1–2% for n – 1) on the refractive index is exerted by the change in the polarizability of the gas as a result of the change in vibrational temperatures of the mixture′s molecules and due to the excitation of electronic states and the dissociation of the starting components
Author: B. I. Lukhovitskii, A. S. Sharipov, I. V. Arsent′ev, V. V. Kuzmitskii, and O. G. Penyazkov
Keywords: thermal nonequilibrium, molecular vibrations, electronically excited states, polarizability, refractive index, Gladstone–Dale constant, optical diagnostics of fl ows, oxygen, nitrogen
MODELING THE MOTION OF SUPERCAVITATING STRIKERS IN A GROUP GUN-START
The investigation is devoted to an experimental and theoretical research into the high-velocity motion of a group of supercavitating kinetic strikers in water. An experimental launching technique has been developed, and investigations have been conducted into the high-velocity motion of a group of supercavitating strikers on a hydroballistic testing facility, and a calculation procedure has been developed for modeling possible deviations of the strikers′ motion in water in a group start. Experimental data have been obtained on the motion of one and two supercavitating strikers on the initial portion of the path at velocities of the order of 1200 m/s, which serve as initial conditions for identifying the strikers′ deviation from the target at a distance of up to 100 m.
Author: A. N. Ishchenko, S. A. Afanas′eva, S. S. Bondarchuk, V. V. Burkin, A. S. D′yachkovskii, M. V. Khabibullin, and A. V. Chupashev
Keywords: water, supercavitating kinetic striker, cavitator, group launching, mathematical modeling, hydroballistic path
SEPARATING LOSS IN AXIAL-FLOW-TURBINE CASCADES
The use of a system of basic hydrogasdynamic equations, which was written for the portion of contraction of the fl ow at entry into a cascade of axial-fl ow turbine profi les at large angles of reattachment to the walls of a blade passage, has enabled the authors to obtain analytical dependences (characteristics) of the loss on the angles of entry of the fl ow into the cascade. The obtained procedure of calculating the loss permits taking account of the radius of rounding of the profi les at entry, on which the region of insensitivity to the angle of attack is dependent, and also determining relevant fl ow-entry angles limiting the insensitivity region. The authors have proposed variants of the procedure for both an incompressible-fl uid model and a compressible gas, where use is made of the gasdynamic functions of the reduced velocity. The calculated characteristics of the turbine cascades are in good agreement with the existing experimental data in a wide range of angles of attack and radii of rounding of the profi les′ leading edges. The infl uence of the fl ow compressibility on the loss has been shown. To test the procedure under the conditions of pulsed fl ow through the turbine where the angles of attack are particularly large, the authors carried out investigations whose results are also in good agreement with the results of corresponding calculations.
Author: Yu. A. Grishin and V. N. Bakulin
Keywords: turbine, angle of attack, separating loss, system of equations, characteristics, gasdynamic functions
ON CALCULATION OF FLOWS OF HETEROGENEOUS MEDIA IN A BODY-FORCE FIELD
With the generalized equilibrium model of a gas-liquid mixture that was proposed by the authors earlier, the spreading of a liquid column in the presence of gravity forces is calculated using the nodal method of characteristics, which is generalized to a multidimensional case.
Author: V. S. Surov
Keywords: gravity, hyperbolic model of a medium, multidimensional nodal method of characteristics
INFLUENCE OF THE WATER FEED TO THE BODY OF A ROCKET-ENGINE EXHAUST JET DURING ITS FLOW INTO A SUBMERGED SPACE
Elements of a homogeneous algorithm for numerical simulation of the thermogasdynamic parameters of a viscous two-phase nonequilibrium chemically reactive nonisobaric rocket-engine exhaust jet have been formulated within the framework of a two-velocity and two-temperature continuum model on the basis of "viscous-layer" and "narrowchannel" equations. By numerical calculation, the authors has established the basic regularities of the infl uence of the water feed, the mixing of the jet with air, and the afterburning of the high-temperature rocket-engine jet in the air oxygen on the fl ow structure and thermogasdynamic and thermophysical parameters of the jet
Author: V. I. Timoshenko
Keywords: viscous two-phase jet, combustion products, water injection, marching methods of solution
FEATURES OF HIGH-VELOCITY PULSATING LIQUID JETS
Processes proceeding in a pulsed liquid-jet generator were investigated in the acoustic and gasdynamic approximations. In the acoustic approximation, the problem on the one-dimensional movement of the liquid in the generator with no movement of its piston and no liquid outfl ow from it was considered. In the gasdynamic approximation, the problems on one-dimensional and axisymmetric liquid fl ows in the generator were solved numerically with regard for the movement of the generator piston, the liquid outfl ow from the generator, and the cavitation of the liquid in it. A onedimensional liquid fl ow in the generator was calculated using the potential method, a scheme with introduction of artifi cial viscosity, the Godunov method, and modifi cations of this method. Results of calculations of the movement of the liquid in the generator by different models were compared, and corresponding conclusions have been made.
Author: A. N. Semko and O. V. Kazak
Keywords: pulsed liquid-jet generator, liquid compressibility, wave process, cavitation, numerical simulation, velocity pulsations, liquid outfl ow, liquid disks
SPHERICAL SHOCK GENERATED BY A MOVING PISTON IN A NONIDEAL GAS UNDER GRAVITATION FIELD WITH MONOCHROMATIC RADIATION AND MAGNETIC FIELD
Similarity solutions for the propagation of a spherical shock wave generated by a moving piston in a nonideal gas under the infl uence of a gravitational fi eld and azimuthal magnetic fi eld with monochromatic radiation are obtained. The gravitational fi eld is due to a central mass at the origin, i.e., the Roche model is valid. The gravitational effect of the gas itself is neglected in comparison with the attraction of the central mass at the origin. We considered that the radiation fl ux moves through an electrically conducting nonideal gas with constant intensity and energy is absorbed only behind the shock which moves in the direction opposite to the radiation fl ux. The results are discussed and compared with ones for a perfect gas, as well as for the cases of the infl uence of the gravitational fi eld and of the absence of this fi eld. The effect of the variations of the Alfven–Mach number, gravitational parameter, adiabatic exponent, and of the parameter of gas nonidealness are discussed in details.
Author: G. Nath
Keywords: shock wave, monochromatic radiation, gravitational fi eld, magnetic fi eld, nonideal gas, interstellar medium
UNIQUENESS OF A SOLUTION TO PROBLEMS OF IDENTIFICATION OF MATHEMATICAL HEAT-TRANSFER MODELS WITH LUMPED PARAMETERS
An analysis has been made of the problem of identifi cation of mathematical heat-transfer models with lumped parameters that have a nonunique solution. The authors have investigated the possibility of restoring conditionally the uniqueness of a solution to such a problem with supplementary conditions for the selection of solutions in the form of linearly independent time functions of temperature that can be obtained in one experiment with relevant designing, Consideration has been given to the applicability of iteration-regularization methods with a vector regularization parameter to identifying a full set of functions of a thermal-state matrix of mathematical models with lumped parameters. On the basis of computational experiments, the capabilities of a variational principle of selection of solutions for conditionally correct identifi cation problems have been demonstrated.
Author: A. G. Vikulov and A. V. Nenarokomov
Keywords: mathematical models, inverse problems, identifi cation, uniqueness and stability of a solution, regularization, variational method, heat transfer
COMBINED METHOD OF SEPARATION OF VARIABLES. 1. CRITICAL ANALYSIS OF THE KNOWN APPROACH
For the purpose of development of a new high-accuracy method of separation of variables, allowing one to effectively use the method of differential transformations in combination with the method of weighted residuals, by the example of the problems on the nonstationary heat conduction of an unbounded plate, an unbounded cylinder, and a sphere with the fi rst-kind boundary conditions, a critical analysis of the known solution technique based on the combined use of the Fourier method of separation of variables, the method of differential transformations, and the method of weighted residuals has been performed. It is shown that the computational scheme realized with the indicated technique has a very low approximation accuracy, especially in the case where it is used for bodies of cylindrical and spherical symmetry. The main reasons for the low accuracy of the solutions obtained by this scheme were revealed.
Author: V. A. Kot
Keywords: heat conduction equation, boundary-value problem, method of separation of variables, weighted residual method, eigenvalues, eigenfunctions, method of differential transformations
EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER OF PLANE HEAT-REMOVING SURFACES WITH PLATE FINNING
Heat transfer of promising heat-removing surfaces with plate-slit fi nning intended for use in the case of air cooling of heat loaded radio- and microelectronic facilities in forced convection regime has been investigated experimentally. The infl uence of the depth of slitting fi ns and of the turning angle of their slit parts relative to the cooling fl ow direction on the intensity of heat transfer of the fi nned surface is shown. It has been established that the greatest intensifying effect is observed at the relative depth of the slitting of fi ns equal to 0.6, which leads to an increase in the intensity of heat release by 20–25%. The turning of the slit parts of the fi ns leads to heat transfer growth by 50–60% compared with traditional plate-fi nned surfaces. Improved dimensionless equations are suggested for calculating average heat transfer of surfaces with plate-slit fi nning under the conditions of forced convection in the range of the Reynolds number values from 2000 to 10,000. The results of investigation can be used in designing new systems of cooling radio- and microelectronic facilities.
Author: A. V. Baranyuk, V. A. Rogachev, Yu. V. Zhukova, A. M. Terekh, and A. I. Rudenko
Keywords: radiator, heat-removing surface, fi nning, convective heat transfer, experiment
STRESSES IN A LUMBER PILE IN THE PROCESS OF DRYING IN A CONVECTIVE DRIER
Numerical calculation of the three-dimensional stress–strain state of a lumber pile in the process of drying in a convective drier is presented. The solution is obtained with the aid of the program complex ANSYS allowing one to develop and visualize three-dimensional geometric constructions. The results of the work can be used for carrying out computational experiments on drying materials in chambers and in developing the regimes of drying lumber piles by analyzing their stress–strain state and for designing drying facilities
Author: V. A. Sychevskii
Keywords: convective drier, lumber pile, numerical calculation, computational experiment
ULTRASONIC INTENSIFICATION OF LOW-TEMPERATURE PLASMA SYNTHESIS OF CERAMIC-LIKE COATINGS OF VALVE METALS
The authors have presented a method of ultrasonic intensifi cation of anode–cathode interactions during the formation, in water–alkali electrolytes, of ceramic-like coatings on the surface of valve metals in the process of lowtemperature plasma synthesis. An algorithm of directional infl uence of high-energy fi elds on the distinctive features and rate of chemical reactions at the electrolyte–metal–coating interface through changing the solution′s state by ultrasonic pulses in the process of anodic microarc oxidation has been developed. The authors have elucidated the mechanism and have determined the character and level of effect of the proposed intensifi cation on the dynamics of growth of a coating under low-temperature-plasma conditions of a liquid medium. It has been shown that mechanical (ultrasonic) activation of the electrolyte is responsible for the intensifi cation of the process of transfer of charge carriers, which are primarily electrolyte ions. Procedures and equipment have been described using which the values of an ultrasonic signal formed under various conditions were recorded. The nature of more intense buildup in the thickness of a ceramic-like coating with reduced energy expenditure to form it has been elucidated. This is explained by the appearance in the electrolyte, during its ultrasonic activation, of the great number of high-frequency damped oscillations of irregular waveform with a high amplitude as far as the current is concerned (5 A or higher), which is attributable to the occurrence of a synergetic effect
Author: N. M. Chigrinova and V. E. Chigrinov
Keywords: ultrasonic intensifi cation, high-frequency damped oscillations of irregular waveform, oscillograms, sweep
RECYCLING OF ORGANIC WASTE IN A PLASMA REACTOR
Thermodynamic calculations and experiments on plasma gasifi cation of wood waste have been conducted. On the basis of a verifi ed TERRA universal thermodynamic-calculation program, the authors have conducted an experiment on plasma recycling of agricultural waste. No detrimental impurities were found in the products of plasma recycling
Author: V. E. Messerle A. L. Mossé, A. B. Ustimenko, N. A. Slavinskay and Zh. Zh. Sitdikov
Keywords: organic waste, agricultural waste, plasma treatment, plasma reactor
ESTIMATION OF THE PARAMETERS OF COMBUSTION OF THE SURFACE OF NATURAL COMBUSTIBLE MATERIALS BY THE THERMOGRAPHY METHOD
The results of an experimental investigation into the parameters of combustion of peat and wood using thermography have been presented. The mechanism of propagation of smoldering over the peat surface has been identifi ed. The temperature fi eld on the surface of peat during its combustion under the infl uence of a local heat source has been obtained, and the velocity of propagation of the smoldering front has been estimated. Using the IR-diagnostics method, temperature distributions have been obtained over the surface of wood specimens exposed to heat action under conditions of a ground fi re with and without fi re-retardant treatment.
Author: M. V. Agafontsev and D. P. Kasymov
Keywords: thermography, wood, fi re retardant, combustion, peat
IGNITION OF COAL MICROPARTICLES IN AN AIR ATMOSPHERE AND THEIR INFLUENCE ON THE INFLAMMATION OF METHANE
The spontaneous combustion of the coal microparticles of fractions 1–20 μm and 20–32 μm in an air atmosphere and the infl ammation of the coal microparticles of fraction 20–32 μm in a methane–air mixture at temperatures of 700–1100 K were investigated with the use of a rapid compression machine. A contactless measurement of the temperature of the coal particles ignited spontaneously in a gas has shown that this temperature can reach 2500 ± 200 K and substantially exceeds the temperature of the gas at the end of its compression stroke. It was established that the coal microparticles burning in a stoichiometric methane–air mixture are local hotbeds of fi re in this mixture at a temperature as high as 1400 K and that the gas is ignited in the neighborhood of these hotbeds. The limiting temperatures of ignition of the coal microparticles in an air atmosphere free of methane and in a methane– air mixture were determined. The measured times of delay in the ignition of the methane by the coal microparticles in a hybrid methane–air mixture agree with the delay times of ignition of a pure methane–air mixture under the same conditions to within the experimental error.
Author: V. V. Leshchevich, O. G. Penyazkov, and S. Yu. Shimchenk
Keywords: ignition, hybrid mixture, methane, coal microparticles, rapid compression machine
TENSILE STRENGTH OF NANOFIBROUS CONCRETE
Results of testing nanofi brous-concrete test beams for axial tensile strength, for cleavage tensile strength, and for compressive strength have been given. Concrete matrices covering a broad spectrum of compressive-strength classes of concretes of construction grade were used as a basis. A macrolevel fi ber (steel or polymeric) or a nanolevel fi ber (carbon nanotubes) was made part of a concrete matrix. An increase of 80% in the axial tensile strength and of 145% in the cleavage tensile strength was recorded in the nanofi brous-concrete test pieces. Diagrams of axial tensile straining of the test pieces have been obtained.
Author: E. A. Sadovskaya, S. N. Leonovich S. A. Zhdanok, and E. N. Polonina
Keywords: nanostructured carbon, nanotubes, fi ber, nanofi brous concrete, axial tensile, cleavage, and compressive strength
HIGH-EFFICIENCY SELECTIVE SOLAR ABSORBER FROM NANOSTRUCTURED CARBONIZED PLANT RAW MATERIAL
The results of investigation into the absorptivity of carbonized rice-husk plant material with regard to solar radiation have been given. It has been shown that an absorber based on leached carbonized rice husk has higher solar absorptivity than an absorber based on carbonized apricot pits with an Apricus coating and an absorber based on a commercial Chinese-made coating. The results of investigation into the physical and chemical properties of carbonized rice husk have been presented. It has been shown that the carbon content in the initial unleached rice husk powder is 82.3%, and after leaching, the percentage of carbon rises up to 93.3%. Based on the results of a BET (Brunauer–Emmet–Teller) analysis, it has been established that leached rice husk has a more developed specifi c surface (447–641 m2 /g) and a higher specifi c volume of pores (0.27–0.392 cm2 /g) than unleached rice husk (127–160 m2 /g and 0.054–0.127 cm2 /g respectively). The advantage of the considered plant-based carbon materials compared to the exiting coatings lies in their porous structure. Cavities are known to be a model of a blackbody, which is a decisive factor in using a material as an absorber, and, simultaneously, a porous structure has a heatinsulating property.
Author: N. G. Prikhod′ko, G. T. Smagulova, M. Nazhipkyzy, N. B. Rakhymzhan, T. S. Temirgalieva, B. T. LesbaevA. A. Zakhidov, and Z. A. Mansurov
Keywords: carbonized rice husk, solar absorber, carbon maternal, solar collector, effi ciency of absorption of solar energy
ICE FORMATION AND FILM FLOW OF WATER ON VERTICAL AND INCLINED PACKINGS
This paper presents the results of studies on the formation of ice on vertical and inclined packings manufactured from a cord of diameters 2 and 5 mm or a wire. Water was sprayed by a rotating disk onto the walls of a pipe of diameter 200 mm where it was cooled and fell on the cord packings without the action of special distributing devices. Periodic protrusions and troughs appeared on the packings just as in the case of formation of icicles. The presence of the cord made it possible to obtain long stalactites as opposed to icicles that grow due to the freezing of their tips and cease to grow at large wetting densities. At the lower parts of the packings tilted at angles of 20–25o , a toothed ice was formed without separation of drops and icicles. The thicknesses of water fi lms and heat transfer coeffi cients were calculated for air fl ow across the packings. Good agreement of the results of calculations with corresponding experimental data has been obtained.
Author: I. I. Pukhovoi
Keywords: cord packings, water fi lms, heat transfer, ice formation, ice accumulation, ventilation, heat pumps.
ACTIVATION ENERGY OF THE CONDUCTANCE OF p–n-4H-SiC Al STRUCTURES DOPED WITH ALUMINUM BY THE METHOD OF LOW-TEMPERATURE DIFFUSION
A study has been made of the activation energy of the conductance of a p–n-4H-SiC Al structure created through the doping of silicon carbide with aluminum. The doping was implemented by a novel method of low-temperature diffusion, in which the diffusion of aluminum in silicon carbide is stimulated by a carbon- and silicon-vacancy fl ux produced by the oxidation of the silicon surface.
Author: Kh. N. Zhuraev, A. Yusupov, A. G. Gulyamov, M. U. Khazhiev, D. Sh. Saidov, and N. B. Adilov
Keywords: 4H-SiC, p–n junction, low-temperature diffusion, activation energy.