Volume 97, №7

LOOP HEAT PIPES: DEVELOPMENT, RESEARCH, APPLICATION

The article presents the basic conditions for the performance of loop heat pipes, criteria for selecting a working fl uid, various design options for such pipes, the results of study of their operating characteristics, and examples of the practical use of these pipes in systems of cooling various technical facilities
Author:  Yu. F. Maydanik, M. S. Chernysheva
Keywords:  loop heat pipe, heat transmission, cooling system
Page:  1653

ADSORPTION THERMAL CONVERTERS OF SOLAR RADIATION AND WASTE THERMAL ENERGY OF VARIOUS DEVICES BASED ON SOLID SORBENTS AND HEAT PIPES

Renewable sources of energy (solar radiation, heat of the ground, etc.) are of substantial interest as an alternative to an organic fuel (coal, oil, and gas). Since the heat-fl ux density is low when renewable energy sources are used, heat exchangers with a large heat-transfer surface should be used to utilize them. Heat pipes and thermosyphons of large length together with heat transformers on solid and liquid sorbents are some of the most effi cient heat-exchange devices intended to utilize renewable energy sources. Solar dryers, water heaters, and demineralized water generators using solar energy are among the most signifi cant applications not associated with electric power stations. Furthermore, the production of hot water is an important consumption of solar energy in the construction industry because of its economic benefi t. The cooling of components of electric and hybrid cars and of aircraft equipment, and also of other transportation vehicles using solar energy on the basis of adsorption thermal converters, heat pipes, and thermosyphons ensures the reliability and economy of operation of onboard equipment.
Author:  L. L. Vasiliev
Keywords:  adsorbents, solar radiation, thermal regulation, heat pipe, thermosyphon, heat exchanger
Page:  1666

SOLUTION TO THE PROBLEM OF THERMAL CONTACT BETWEEN THE WICK AND THE BODY OF A FLAT HEAT PIPE BY MEANS OF A BAROTHERMIC PROCESS

A fl at heat pipe with the dimensions of 150 × 30 × 3 mm with an improved thermal contact between the wick and the body has been developed and fabricated. The body was made using chemical etching of a copper billet; the heattransfer agent was water; the wick was made up of brass meshes soldered to the body by means of a barothermic process. An experimental sample of a fl at heat pipe has been investigated at various heat loads. The hydrodynamic boundary of the pipe is 106 ± 2 W; the optimum transmission capacity is 75.2 ± 1.1 W at the thermal resistance 0.044 ± 0.011 K/W. The paper shows the advantages of the developed technology of wick formation by means of a barothermic process due to a reduction in thermal resistance with increase in the transmitted power of the heat pipe.
Author:  O. L. Voitik, K. I. Delendik, N. V. Kolyago
Keywords:  fl at heat pipe, wick, thermal resistance, porosity, permeability, barothermic process
Page:  1680

HEAT AND MASS TRANSFER IN A LOCAL ENCLOSED OPERATING ZONE UNDER RADIANT HEATING CONDITIONS

The paper presents the results of mathematical simulation of the processes of heat transfer and diff usion of natural gas released during combustion of natural gas in a gas infrared emitter burner, which is a source of heat and carbon dioxide supplied to the local operating zone of a large-sized production area. Numerical studies are carried out taking into account the infl uence of the air exchange systems on the heat and mass transfer processes in the room and the equipment located in it. The problem is solved in a fl at formulation using the approximation of the k–ε model of turbulence for the fl ow of a gas mixture in the local operating zone and its small vicinity on supply of a relatively cold "fresh" air from the air exchange system. The concentration fi elds of CO₂ and the distribution of carbon dioxide values in a locally enclosed small-sized operating area showed an impact of the enclosure of the CO₂ concentration and air exchange intensity. A signifi cant infl uence of local baffl es on the temperature fi elds of operating zones and intensity of air circulation in such zones was also established. The possibility of controlling the composition and temperature of air in a local operating zone by varying the sizes and materials of the local enclosure was substantiated
Author:  G. V. Kuznetsov, B. V. Borisov, V. I. Maksimov, T. A. Nagornova, S. O. Salagaev, F. Yu. Salikhov
Keywords:  gas infrared emitter, temperature regime, CO2 concentration fi elds, local enclosure, air exchange system
Page:  1688

MODELING THE PROCESS OF HEATING OF A THREE-LAYER STRAIN-JOINT FILLER IN A MICROWAVE-RANGE ELECTROMAGNETIC FIELD

The authors have presented a mathematical model of dielectric heating of a three-layer strain joint of a rigid aerodrome pavement, and also the results of a numerical experiment which allow predicting the characteristics of a temperature fi eld as functions of the velocity of motion of a microwave radiator
Author:  V. R. Dornyak, A. B. Nedonoskov, Z. A. Shabunina
Keywords:  microwave heating, mathematical modeling, electromagnetic fi eld, temperature, strain joint
Page:  1697

EFFECT OF VOLUME CONDENSATION ON THE INTENSITY OF HEAT AND MASS TRANSFER

The paper presents the results of solving the problem of liquid evaporation and its vapor condensation in a closed space with regard to the formation of droplets in it as a result of homogeneous vapor nucleation, obtained by jointly solving the Boltzmann kinetic equation and the equations of continuum mechanics. The kinetics of homogeneous vapor condensation is described by the corresponding system of moment equations. Calculations for water have shown that in the case where the evaporation surface temperature exceeds 330 K, volume condensation of vapor occurs with high intensity, which leads to signifi cant changes in the profi les of its parameters
Author:  V. O. Maiorov, V. Yu. Levashov, A. P. Kryukov
Keywords:  evaporation, volume condensation, homogeneous nucleation, Boltzmann kinetic equation, interface
Page:  1704

INFLUENCE OF GROWING DROPLETS ON THE INTENSITY OF THE RECONDENSATION PROCESS

Results of a numerical simulation of the infl uence of the droplets having variable radii on the intensity of transfer process in the problem on the evaporation of liquid and the condensation of its vapor are presented. On the basis of the preliminary estimates, the possibility of formation of droplets at a distance, equal to several mean free paths of vapor molecules from am evaporation surface, was demonstrated. The calculations were perfumed with regard for the formation of droplets at the stationary and nonstationary stages of the recondensation process on the assumption that the droplets are immovable and that their temperature remains unchanged. It was established that the droplets present in a vapor fl ow, whose sizes increase as a result of the condensation of vapor on them, can substantially infl uence the intensity of mass transfer in the vapor fl ow and that this infl uence decreases substantially or disappears in the process of movement of the droplets and with increase in their temperature
Author:  V. Yu. Levashov, I. N. Shishkova, A. P. Kryukov
Keywords:  vapor, droplets, evaporation, homogeneous condensation, Boltzmann kinetic equation
Page:  1710

NUMERICAL SOLUTION OF THE KINETIC EQUATION FOR THE SIZE DISTRIBUTION FUNCTION OF PARTICLES WITH REGARD FOR THEIR COAGULATION

As an alternative to the known sorption methods used for the cleaning of gases from impurities, the volume condensation of carbon dioxide from its mixture with air in the divergent part of a Laval nozzle is considered. This process is defi ned by the kinetic equation for the size (mass) distribution function of particles, in which the Brownian coagulation of particles is estimated in the two-temperature approximation and which, in the one-dimensional form, is solved by the direct numerical method and, in the three-dimensional form, with the use of the special computational module "Volume Condensation" integrated into the computational CFD package. The distributions of parameters of condensing aerosol along the central axis of the nozzle with and without coagulation of its particles have been obtained. It is shown that, as a result of the coagulation of particles in this aerosol, their number in it decreases. In this case, the size of the particles increases, but their mass remains unchanged. It was established that the contribution of the coagulation of particles in a vapor–gas mixture into their growth exceeds 10% and increases with a rate of expansion of a mixture fl ow. The results obtained agree qualitatively with the results of the corresponding experiments.
Author:  A. A. Sidorov, A. K. Yastrebov
Keywords:  volume condensation, coagulation, carbon dioxide, air-separation plant, numerical solution, kinetic equation
Page:  1719

COMPARISON OF THE VIBRATIONS OF THE HELIUM-II–VAPOR INTERFACE IN A U-SHAPED CHANNEL WITH A MONODISPERSE BACKFILL AND WITHOUT IT

Experimental data on the movement of the superfl uid helium in a U-shaped cylindrical channel fi lled with and without a permeable porous backfi ll of metal monodisperse spheres are considered. The results of experiments are presented in the form of the time dependences of the position of the helium-II–vapor interface in the channel. A comparison of the amplitudes and frequencies of vibration of this interface, depending on the pressure in the channel, in the cases of free channel and where it is fi lled with porous backfi ll has been performed. It is shown that, in the channel with a monodisperse porous backfi ll, a stationary state of the interface is possible
Author:  Yu. Yu. Puzina, A. P. Kryukov
Keywords:  superfl uid helium, experiment, channel, vibrations, monodisperse backfi ll, heat fl ow, interface
Page:  1727

HEAT TRANSFER CRISIS IN SUBCOOLED WATER BOILING IN MACRO-, MINI, AND MICROCHANNELS

The paper presents the results of investigation into the crisis heat transfer in subcooled water boiling in macro-, mini-, and microchannels without coating and with porous coating. The equation for calculating the critical thermal load (CTL) in macro-, mini, and microchannels without coating is based on the analysis of arrays of experimental data obtained in investigating critical heat fl ux in subcooled water boiling in wide ranges of diameters, pressures, mass velocities and vapor contents. The calculation of the critical thermal load during boiling in a channel with porous coating has been conducted according to the previously developed formula for a horizontal 8-mm-diameter tube with a one-side heating. A porous coating in a macro-channel results in an almost threefold CTL rise. For a microchannel with a porous nanoparticle coating, CTL, at comparable mass velocities, is 1.5 times higher than without coating. The suggested equations for both channels without coating and channels with a porous coating describe the experimental data on critical thermal loads in macro-, mini-, and microchannels in the considered ranges of regime parameters with a deviation of no more than 30%.
Author:  Yu. A. Kuzma-Kichta, A. S. Komendantov, A. F. Krug, A. S. Kiselev
Keywords:  microchannel, minichannel, macrochannel, critical thermal load, heat transfer enhancement, porous coating
Page:  1735

KINETICS OF CATALYTIC HYDROLYSIS OF AQUEOUS AND AQUEOUS-ALKALINE SODIUM BOROHYDRIDE SOLUTIONS

The infl uence of temperature, as well as NaOH and NaBH₄ concentrations on the rate of catalytic hydrolysis is investigated. Finely dispersed powders of platinum and ruthenium on a titanium oxide carrier were used as model catalysts. The activation energies in an aqueous and aqueous-alkaline solutions of NaBH₄, equal to 60.5 and 53.2 kJ/mole for Pt/TiO₂ and 62 and 64.65 kJ/mole for Ru/TiO₂, respectively, were determined. It was found that with an increase in the concentration of NaOH, the rate of hydrogen generation with Ru/TiO2 decreases, and with Pt/TiO₂ passes through a maximum in the range 0.5–2 M NaOH. It is shown that with traditional processing of kinetic data for determining the activation energy, its dependence on the sorption properties of the surface and the concentration of the solution is revealed.
Author:  V. G. Minkina, S. I. Shabunya, V. I. Kalinin
Keywords:  sodium borohydride, hydrogen, catalytic hydrolysis, platinum, ruthenium
Page:  1744

EVOLUTION OF THE BOUNDARY LAYER IN A CHANNEL DURING NONSTATIONARY COMBUSTION OF A GAS MIXTURE

The article presents the results of the computational and theoretical analysis of the mechanisms of formation of a vortex fl ow during fl ame propagation in a channel fi lled with a combustible gas mixture. It is shown that at the initial stage of combustion development the fl ow formed in the near-wall region can be described in accordance with the Blasius boundary layer theory. It is established that the nonstationary nature of fl ame evolution leads to disturbance of the boundary layer and that under certain conditions the development of the boundary layer instability determines the formation of vortex structures ahead of the fl ame front. In such a case, depending on the composition of the combustible gas mixture, stable fl ow regimes without the formation of vortex structures and regimes with fl ow stabilization are possible
Author:  A. V. Yarkov, A. D. Kiverin, I. S. Yakovenko
Keywords:  combustion of gases, fl ame acceleration, boundary layer, vortex fl ow, numerical simulation
Page:  1751

A SYSTEM FOR ADAPTIVE SUPPRESSING THE IGNITION OF MATERIALS AND SUBSTANCES

By using a model room, the conditions are reproduced for the functioning of the system of early identifi cation of ignition originated due to the statistically most typical causes and its eff ective suppression are represented due to the timely and reliable information on the type of fi re source, its size and position, and on pyrolyzing material and its mass. The response characteristics of diff erent types of fi re detectors are recorded. Specialized software has been developed that allows accumulating statistics on the response of various types of sensors in a model room, analyzing statistical data and issuing recommendations for the fi re safety system operator. Statistical data are used by a neural network to determine the type of combustible material, its mass, material heating mechanism, and the volume of extinguishing agent necessary and suffi cient to localize and suppress combustion of the material. The proposed adaptive approach to fi re extinguishing allows one to signifi cantly reduce the amount of water required to suppress the fi re source and the time of its extinguishing.
Author:  M. I. Glotov, S. S. Kropotova, P. A. Strizhak
Keywords:  thermal decomposition, ignition, low-inertia identifi cation, adaptive fi re suppression
Page:  1760

ASSESSMENT OF THE POSSIBILITY OF MICROWAVE BIOMASS TORREFACTION USING THE HEAT OF AN EXOTHERMIC DECOMPOSITION REACTION

Numerical and natural experiments have been used to show the possibility of implementing microwave torrefaction of biomass (peat and wood) with particles of carbon fi ller (petroleum coke and graphite) playing simultaneously the role of a microwave radiation absorber and a thermal ballast ensuring the controllability of the process temperature regime occurring with heat release. In this case, part of the heat required for maintaining the working temperature in the process of torrefaction is supplied from an exothermic reaction of biomass decomposition.
Author:  M. A. Brich, N. M. Gorbachev, I. A. Koznacheev, D. S. Makarenko
Keywords:  torrefaction, pyrolysis, biomass, microwave radiation, exothermic reaction, modeling, experiment.
Page:  1770

POTENTIAL FOR USE OF MINERAL RESIDUES FROM POTASSIUM SALTS PRODUCTION AS CATALYSTS OF PYROLYTIC RESIN DECOMPOSITION

The paper discusses the results of an experimental investigation into thermal decomposition of pyrolytic wood resin in a homogeneous process and also in the presence of a mineral residue from potassium salts (MRPS) production. The experiments have been performed on a laboratory setup under isothermal conditions at temperatures of 300, 350, and 400^o C using two techniques ensuring two-phase and three-phase contacts with the catalyst respectively. It has been established that under the studied conditions, the pyrolytic wood resin decomposition rate obeys the laws described by the Avrami–Erofeev equation with the varying exponent n. The average value of the exponent n calculated for all variants of the investigation was 0.694. It has been found that the pyrolytic wood resin decomposition rate rises in the case of introduction of MRPS particles into the reaction zone. The Arrhenius parameters of a homogeneous process of resin thermal decomposition and a decomposition process in MRPS presence have been identifi ed. According to the obtained data, the energy of a homogeneous process′s activation was 29.6 kJ/mol, and the preexponential factor was 3.15·10¹ min^–1 respectively. According to the data from the conducted investigations, the Arrhenius parameters of MRPS pyrolytic resin decomposition were 23.0 kJ/mol and 1.81∙101 min^–1.
Author:  S. V. Vasilevich, M. V. Mal′ko, K. V. Dobrego, D. V. Degterov
Keywords:  pyrolytic resins, minimal residue of potassium production, decomposition kinetics, Arrhenius parameters
Page:  1779

DESIGNING A HEAT SHIELD FROM CARBON AEROGEL-BASED COMPOSITE MATERIAL FOR SPACE VEHICLES

An algorithm of optimum designing a multilayer thermal insulation, based on a carbon aerogel reinforced with a highly porous cellular carbon material, with account of the dependence of the thermophysical properties of the composite material on the microstructure of the reinforcing fi ller is presented. The practical application of the indicated algorithm is illustrated by the example of solving the problem on designing a three-layer heat shield for a solar probe
Author:  O. M. Alifanov, S. A. Budnik, A. V. Nenarokomov, M. O. Salosina
Keywords:  optimization, multilayer heat shield, carbon aerogel, highly porous cellular material
Page:  1788

ON THE GAS DYNAMICS OF THE GRANULAR BED

The laws governing the evolution of a shock wave moving along a granular bed are established. Using the methods of similarity theory, a criterion of shock wave stability is formulated, which includes the main characteristics of a granular bed. A generalization of this criterion to the case of a porous layer is proposed.
Author:  Yu. S. Teplitskii, E. A. Pitsukha, A. R. Roslik
Keywords:  gas dynamics, shock wave, compression wave, granular bed, stability criterion, pipe, attenuation, pressure jump, evolution, resistance force
Page:  1799

HEAT AND MASS TRANSFER IN A VIBROFLUIDIZED BED OF VEGETABLE MATERIALS WITH RADIATIVE-CONVECTIVE POWER INPUT

Results are presented for theoretical and experimental investigations into the kinetics of dehydration and heat and mass transfer in a vibrofl uidized bed of vegetable origin materials using the example of potato and carrot particles in convective and radiative-convective heat inputs. A comparison has been drawn between calculation results and experimental data. The contribution of infrared radiation and convective heat fl ux has been determined. The possibility and regimes of dehydration process enhancement and reduction of its duration in a vibrofl uidized bed in radiative-convective heat input have been shown.
Author:  P. V. Akulich, D. S. Slizhuk, A. V. Akulich
Keywords:  heat and mass transfer in a dispersed layer, radiative-convective drying, drying or dehydration of vegetable materials, drying in a vibrofl uidized bed
Page:  1808

ASYMPTOTIC SOLUTION OF THE PROBLEM OF CONVECTIVE-DIFFUSIVE TRANSFER OF SORBABLE WATER-SOLUBLE COMPOUNDS IN DISPERSED MEDIA WITH REGARD TO THE KINETICS OF SORPTION AND DIFFUSION IN THE PORE SOLUTION

An asymptotic solution has been obtained for the equation of convective diff usion of water-soluble compounds with regard to the sorption kinetics at a linear isotherm of their sorption by a solid dispersed phase and molecular diff usion in a pore solution. It is shown that the calculation error can be signifi cantly reduced by using the shift parameters in the distribution of the concentration of transferred compounds calculated using formulas that take into account the parameters of convective-diff usive transfer. The proposed method can be used to improve the accuracy of calculation and analysis of the infl uence of various initial factors on convective-diff usive transfer of heavy metal compounds and radionuclides in dispersed natural environments.
Author:  G. P. Brovka
Keywords:  natural dispersed media, water-soluble compounds, convective-diff usive transfer, hydrodispersion, asymptotic solution
Page:  1814

DEPOSITION OF NANOPARTICLES AND THEIR AGGLOMERATES FROM A LAMINAR GAS FLOW ONTO A SUBSTRATE

Two universal mechanisms of isothermal deposition of nanoparticles from a gas fl ow (Brownian diff usion and gravitational deposition) are investigated. The results of a model experiment on the deposition of nanoparticle agglomerates from a laminar gas fl ow onto a fl at substrate at room temperature are presented. Disintegration of nanoparticle agglomerates on increase in the fl ow velocity is detected.
Author:  E. S. Golomako, V. I. Saverchenko,S. P. Fisenko
Keywords:  Brownian diff usion coeffi cient, nanoparticle agglomerates, gravitational deposition
Page:  1820

MODELING THE INFLUENCE OF BOILING IN THE CORE OF WWER-1200 ON UNIFORM CORROSION OF THE OUTER SURFACE OF FUEL ELEMENTS

The parameters of the coolant moving in the channel between the fuel elements in the WWER-1200 core with a design steam content of 0.1 at the outlet are determined. The corrosion of the outer surface of these elements is modeled taking into account the heat and mass exchange between the near-wall layer of the coolant fl ow (with a thickness of the order of the thickness of the evaporating microlayer under the steam bubble) and its core. It is found that the concentration of ammonia in the near-wall layer of the fl ow is 0.35 of its concentration in the fl ow core, and this concentration level is typical of the upper half of the core. A formula is proposed for calculating the thickness of the oxidized layer of the outer surface of the fuel elements taking into account the concentration of oxidizers in the near-wall layer of the coolant fl ow. An increase in the thickness of the oxidized layer due to the eff ect of boiling is estimated at 30% compared to the thickness observed upon completion of operation during four annual cycles without boiling.
Author:  V. V. Sorokin
Keywords:  WWER, fuel elements, coolant, boiling, primary coolant circuit, corrosion, zirconium alloy
Page:  1825

NOVEL APPROACHES TO MODELING HEAT TRANSFER IN A LATE STAGE OF A SEVERE CORE-MELTDOWN ACCIDENT AT A WATER-MODERATED WATER-COOLED POWER REACTOR

The authors have described the key features of approaches to numerical modeling of the interaction of the core melt of a water-moderated water-cooled power reactor with the NPP structures, that are aimed at accelerating the calculation to preserve the approximation by using 0D + 2D fi nite-element schemes with an adaptive 2D grid for the wall and a 0D grid for the melt. The composition of the melt of interacting components and their properties, and also the properties of the heating material of the wall are determined in the process of calculation. The given examples of calculations of the thermal erosion of the wall by the melt with in-vessel retention of the melt and melt–concrete interaction illustrate the computational effi ciency of the proposed approaches.
Author:  A. S. Filippov, V. D. Ozrin
Keywords:  light-water reactor, severe accident, heat transfer, in-vessel retention of the melt, fi nite-element method, adaptive grid
Page:  1830

HYDRODYNAMICS AND HEAT TRANSFER IN INTRICATELY SHAPED CHANNELS OF POWER UNITS OF TRANSPORTATION SYSTEMS

The authors have presented the results of modeling of the processes of transfer of various working media in intricately shaped channels, including the case of fl ow-rate and pressure pulsations. An approach has been proposed to creating reliable computer models of a lubrication system and a gas-intake system for an in-line six-cylinder engine. Consideration has been given to the channels of lubrication, gas-exchange and cooling systems for diff erent operation regimes of transportation systems with allowance for the features of functioning of an oil pump, a turbocompressor, and a liquid pump. Based on the results of calculations with the reliable computer model, technical solutions have been proposed for changing the geometry of the channels to reduce the hydraulic loss in them and to equalize the distribution of mass fl ow rates in branching channels
Author:  I. A. Popov, V. M. Gureev, M. V. Gureev, Yu. V. Zhukova, A. D. Chorny, T. A. Baranova, I. G. Kukharchuk, I. A. Popov Jr.
Keywords:  nonstationary fl ows, heat transfer, intricately shaped channel, diesel engines, digital twin, reliable computer model, mathematical model
Page:  1840

CHARACTERISTIC FEATURES OF MODELING MULTIPHASE FLOWS IN THE HELE-SHAW CELL

A two-phase fl uid fl ow in a Hele–Shaw cell is considered. A series of experiments on stable displacement from the cell is described. A discrepancy between experimental data and analytical solutions based on the generally accepted mathematical model for describing fl ows in a Hele–Shaw cell is shown. A modifi ed mathematical model with a correcting resistance coeffi cient determined empirically is proposed. The new semiempirical model provides good agreement with experimental data. The results of numerical modeling of unstable fl ow in a Hele–Shaw cell are also presented.
Author:  E. I. Skrylyova, L. A. Paremskaya, A. N. Manakhova, V. V. Tyurenkova, F. Chen, Yu. Mengc
Keywords:  Hele-Shaw cell, multiphase fl ows, fi ltration fl ows, analog modeling
Page:  1854

APPROXIMATION OF FLOW CURVES OF MAGNETORHEOLOGICAL FLUIDS

The authors have investigated, with the rotational viscometer, the rheological characteristics of magnetorheological fl uids with a dispersed phase both on the basis of particles of carbonyl iron only and with additions of a ferrimagnetic oxide fi ller. Flow curves obtained by regression-analysis methods have been approximated by a power function with three parameters dependent on the magnetic fi eld strength and the concentration of the dispersed phase.
Author:  M. Zhurauski, E. V. Korobko, L. V. Markova, L. V. Radkevich
Keywords:  magnetorheological fl uid, tangential stress, control algorithm
Page:  1862

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