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The current research simulates the mass and heat energy transmission model on MHD fluid flow under concentration and temperature deviations on a two-dimensional viscous fluid along an upright facet. Following boundary layer estimations, mathematical simulations for the movement of fluids, the conveyance of heat and mass exposed to radiation, thermophoresis, and Dufour consequences are generated as a set of partial differential equations. The surface's resilient suction was assessed. The built-in solver bvp4c in MATLAB is used for numerically debugging the aforementioned models. Through the inclusion of visualizations and tables, the detrimental effects of influencing variables are examined on the velocity, temperature as well as concentration gradients in conjunction with on the skin friction, Nusselt number, and Sherwood number. Excellent coherence may be shown when comparing between the most present findings and those that have previously been made available in the literature in specific limited circumstances. The Dufour effect, radiation, thermophoresis, and the Grashof number are all factors that influence fluid motion and heat transmission at the interface layer of dirt. Moreover, developments in the Shearing stress, Nusselt number, and Sherwood number coefficient are calculated. The findings are crucial for optimizing a variety of fluid-based technologies and systems, allowing developments in a number of industries including energy-effectiveness, electronics cooling, pursued medicine administration, and many more.

The study of the boiling liquids processes is currently relevant, as it affects many energy areas and can offer new ways to improve the efficiency of energy plants. The properties and the nanolayer formation processes on the heater surface are the area of interest. Modification of the heater surface in power machinery with the formation of a porous layer on them is more promising than using nanofluid as a heat transfer fluid. The research of the nanolayer formation a during boiling provides insights into its properties and its effect on heat transfer during boiling. It has been experimentally established that when the suspension boils, porous deposits form on the heat exchange surface. Initially, the roughness caused by the deposition of nanoparticles increases, but after a while it begins to decrease due to the alignment of the sediment profile.

The current study presents the results of a numerical investigation of thermal radiation's consequences, ohmic heating, and electromagnetic hydrodynamic drag on the Casson fluid flow across a flat surface. By incorporating suitable similarity parameters, the equations that regulate the system are converted into non-linear ordinary differential equations. The MATLAB Bvp4c algorithm is used for computing nonlinear ODEs numerically. To optimize the industrial and ecological processing, it is crucial to study the flow of Casson fluids (including drilling muds, fossilised coatings, different sedimentation, and specific lubricating petroleum products, polyethylene dissolves, and a range of colloids) in the presence of heat transmission. Graphics and tables have been employed to present computational findings for various spans of the tangible variables that dictate the velocity and temperature distributions. The fluid rate decreases when the magnetic and Casson parameters rise, whereas fluid velocity increases as the local electric parameters grow. This exemplifies the intricate relationship between electromagnetic radiation and fluid mechanics. Growing Eckert number, thermal radiation, specific heat, and Biot number boost temperature profiles, whereas growing Casson parameter and local electric parameters diminish them, showing diverse impacts on heat transmission phenomena. Additionally, this inquiry pertains to the coefficient of skin friction and Nusselt values were covered. New experimental studies will benefit from this theoretical work, nevertheless.

Background. The purpose of the work is the numerical modeling of unsteady convective heat exchange of an electrically conductive fluid between two concentric spheres, taking into account the dissipation of Joule heat, viscous, inertial, lifting and magnetic forces at low values of the magnetic Reynolds number. Materials and methods. Foe solving the problem, the finite element method is used. In a dimensionless form, the problem in the variables vortex, stream function, temperature and magnetic induction is solved in a spherical coordinate system, taking into account symmetry in longitude. Results. Nonstationary temperature fields, a stream function field, a vortex field, fields of the radial and azimuthal components of magnetic induction and the distribution of local Nusselt numbers in a spherical layer of an electrically conductive liquid for small values of the magnetic Reynolds number were obtained. Conclusions. The results obtained in the work can be applied in the study of magnetohydrodynamic and thermal processes and their application for the development of new installations and instruments, the creation of new methods and models, and expanding the understanding of the nature of the occurrence of magnetohydrodynamic phenomena taking into account heat and mass transfer processes.

A study to look at how heat and mass transfer affect unsteady MHD flow across an accelerated plate with changing temperature and mass diffusion in the appearance of a heat source (or sink) through a porous medium is presented. Initially, the temperature and concentration of the fluid and plate are considered to be the same at t′ ≤ 0. At t′ > 0, an impulsive uniform acceleration A is applied to the plate in a vertical upward direction. The non-dimensionalised governing equations defining the flow problem are solved using Laplace transform approach. Effect of various physical quantities involved in the velocity, concentration, temperature, the rate of heat transfer and also the rate of mass transfer are investigated through graphs and tables and discussed.

To solve the problem of useful utilization (by combustion in heat generators) of liquid and gaseous industrial waste (that was defined in Part 1 of the present article), heat transfer processes in heat generating units were considered in Part 2. The main equipment for the effective solution of this process is a burner device and a combustion chamber with heat transfer to an external heat carrier, for example, a boiler furnace or a heat recovery boiler. The present article considers an example of calculating such a process for a distinctive mixture of waste from a chemical industry enterprise using modeling of possible schemes of a flame combustion system for a characteristic combination of various types of gaseous and liquid combustible products. For this purpose, the CFD (Computational Fluid Dynamics) computational hydrodynamics method was applied, which is determined to be the most effective one, in analyzing the behavior of media flows and combustion processes. CFD analysis makes it possible to predict hydrodynamic and thermal processes (especially in complex multicomponent systems) and optimize them to achieve the best results. The most important factor in high-quality combustion is the atomization process (fine atomization) of highly viscous liquids with high surface tension coefficients. The ultrasonic me-thod has been adopted as the most effective for such liquids. Besides, the quality of the distribution of flows of combustion mixtures and flue gases in the combustion chamber is considered. For doing this, it is necessary to arrange separate flows of axial and peripheral air, which make it possible not only to change the configuration of the flame, but also to direct convective flue gas flows to the most efficient areas of the combustion chamber. The article considers various options for heat transfer (convective and radial) depending on various factors, taking into account the degree of probability of formation of pollutants (primarily NOx) in combustion products. The results of the numerical solution of the problem are presented. The analysis of the results on the optimal ratio of the shares of primary and secondary air flows for combustion was carried out. In conclusion, a comparative analysis of the options for burning fuel directly in the boiler and in the pre-combustion chamber is presented. The efficiency of direct combustion has been demonstrated.

A Stefan problem of heat transfer in semi-infinite bodies with an arbitrary number of unsteady moving boundaries during phase transitions was solved. Such problems arise when composite materials are heated at high temperatures, causing the binding agents to decompose (destruct) thermally, which leads to the formation of moving boundaries in the onset and end of phase transitions, mass transfer, etc. An analytical solution of the Stefan problem with an arbitrary number of unsteady moving boundaries was obtained. The heat transfer process with two moving boundaries was analyzed.

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

During the dry season, some parts of Indonesia experience drought and a clean water crisis, resulting in scarcity and difficulty in drinking water. One of the solutions to solve this problem is to use an air-water harvester machine that produces water from the air. Since the intake air temperature affected the water yield, the article examined the relationship between the engine intake air temperature and the machine’s performance. The study aimed to determine the performance of the air-water harvester machine at various air intake temperatures. The research was carried out experimentally for a refrigerant working fluid R134a. The rotary-type 1/4 PK compressor was used to realize the research. The air temperatures entering the condensing unit varied between 30, 35, and 40 °C. The results showed that the highest average water mass obtained was 0.34 kg at a temperature variation of 30 °C. The highest total heat absorbed by the condensing unit from the air of 184 W occurred at a temperature variation of 40 °C. Overall, an increase in the air intake temperatures allowed for a decrease in the performance of the air-water harvester machine by more than 5 %.

Relevance. Ensured by well-known theses about energy security and transition to alternative energy sources, reducing environmental emissions and energy saving in various industries through the use of geothermal energy. The study of the thermal regimes of deposits of geothermal energy sources located in zones of permafrost is of particular interest. The operation of geothermal wells in permafrost is associated not only with the danger of collapses in the wellhead zone, but also with the destruction of well structures with the withdrawal of their operation for long periods of time. Aim. Numerical analysis of heat transfer in the area where geothermal wells are located, taking into account the real characteristics of a typical geological section to predict the thawing of permafrost in Eastern Siberia. Object. Typical geothermal well design, the main elements of which (columns, conductor and directions) are made of cement. Methods. The simple iteration cycle was used in conjunction with the methods of two fractional steps according to the splitting scheme and the sweep method to solve the problem by the finite difference method. At nodal points belonging to several areas, the thermophysical characteristics were calculated as arithmetic averages. The adequacy of the results of the numerical analysis is confirmed by varying the grid parameters, the energy balance at the boundaries of the calculation area, and comparing the research results with literature data. Results. The authors have carried out the analysis of heat transfer during the operation of geothermal wells in Eastern Siberia, taking into account the actual characteristics of permafrost rocks that vary with depth. It was revealed that the radii of thawing of permafrost for the conditions of Eastern Siberia are 12–17 meters. The feasibility of taking into account the dependence of the thermophysical characteristics of rocks/soils in accordance with the parameters of the geological section during the design, construction and operation of objects using geothermal energy is shown.

This research delves into the study of heat transfer in nanofluids, which are specialized fluids containing nanoparticles. The investigation focuses on understanding crucial factors affecting heat transfer in nanofluids, such as thermal conductivity, viscosity, flow patterns, and density. Both experimental and computational methods are employed to explore how various nanofluid compositions perform in different scenarios. The outcomes of this study contribute to an improved comprehension of nanofluid behavior and its potential applications in enhancing heat transfer processes

In the search for new magnetically ordered phases of materials, solid-state synthesis technologies in reaction crucibles are used. The final result of the synthesis process in reaction crucibles is conditioned, in particular, by technological factors, the mode of current flow and its density, the achieved temperature in the reaction zone, exposure time, geometrical parameters of the crucible and the reaction zone, etc. The paper presents the results of influence investigation of the reaction volume filling degree with tin melt on the processes of heat and mass transfer during its electrothermal treatment. A model describing diffusion processes in the reaction zone during the synthesis of iron and tin intermetallides under electrothermal treatment has been proposed. The diffusion process in the reaction crucibles of the iron-tin system was investigated by the finite element method in the Comsol Multiphysics software environment. It is shown that the decrease in the degree of filling of the reaction crucible with synthesis components leads to a change in the distribution of current density and a decrease in the temperature in the reaction zone, which affects the mass transfer processes. The results of the work can be used in the analysis of experimental data on the production of intermetallides by reaction synthesis and determination of the necessary technological parameters for the synthesis of new materials.

The paper proposes a modern approach to the automated design of three-dimensional models of wood drying chambers and the study of their operation parameters using the SolidWorks Simulation tool, which makes it possible to create various information models using computer tools. Therefore, in this paper, a three-dimensional model of a wood drying chamber was developed and presented, which includes its main components: walls, ceilings, door, stacks of lumber to be dried, a fresh air supply system, a system for its circulation through fans and heating through heaters. For the automated design of three-dimensional models of all these components, the corresponding algorithms were also developed and programmatically implemented using a specialized SolidWorks application programming interface. At the same time, the developed software application takes into account the parameters entered by the user, including the size, quantity, and type of lumber to be dried. In addition, several thermal calculations were performed across the stack, including with different air velocities. This allows us to analyze the effect of this speed on the distribution of heat transfer across the stack. In general, the obtained results are automatically displayed in one of the windows of the software application. This approach makes it possible to obtain results in the background of SolidWorks with minimal user intervention. Despite the fact that such studies are carried out in SolidWorks Simulation, the graphical results, including the temperature distribution across the stack, are fully automated without user intervention. The software application also makes it possible to automatically change the geometry of a three-dimensional model of a wood drying chamber or stacks within specified limits. In turn, the use of the developed software application in combination with SolidWorks Simulation can effectively speed up the process of creating three-dimensional models of wood drying chambers and studying their operation parameters. In general, this work reflects the trend towards digital transformation in industry, opening up new opportunities for woodworking enterprises and contributing to their market competitiveness and production efficiency.

Introduction. One of the most common ways to save heat energy and money is the use of recuperator units in mechanical ventilation systems. In this article, we will talk about the modernized air recuperator. In the process the design feature, layout and operation algorithm of this heat exchanger device will be demonstrated. In order to increase the choice of type and designs of air heat exchangers, designers will be offered and described the variant of designed combined recuperator with an exhaust air intake device from the room, which in the process will be one of the versions of the device increasing the efficiency factor in mechanical ventilation systems. The recuperator is an indispensable element for modern unique buildings and structures.Materials and methods. The recuperator is proposed as an analogue of existing ones and belongs to the field of energy saving in mechanical ventilation systems.Results. The efficiency increase in comparison with analogues is carried out due to: the use of the recuperator as a combined exhaust air intake unit from the room, an increase in the area of contact of heat carriers, a special internal structure capable of more uniform heat transfer, an atypical arrangement of the recuperator installation to avoid freezing and "defrosting" of condensate at the heat transfer surface. The heating flow of the supply air through the combined recuperator with the exhaust air intake device from the room in the mechanical ventilation system is regulated by automation to maintain a more comfortable supply temperature in the room.Conclusions. The new design acquires an increased efficiency compared to its analogues.

Introduction. Engineering systems are an integral part of all buildings. It is they who provide a comfortable stay and provide vital activity for a person. The role of energy-saving measures used in the construction and operation of engineering systems is very important. With the help of these technologies and their improvements, energy conservation of natural resources takes place. Energy efficiency in technology helps humanity to reduce the cost of energy resources, but at the same time to ensure the necessary level of technological processes in buildings. This article will show the problem of energy saving in mechanical ventilation systems. To implement energy-efficient use of resources, an improved recuperator unit with an increased efficiency is proposed. Currently, for engineers, there should be a greater choice of used recuperator designs with an increased efficiency, which can be used for different types of objects and technical conditions.Materials and methods. The recuperator is offered as an analogue of existing samples and relates to the field of energy efficiency in ventilation systems.Results. An increase in efficiency compared to analogues due to an increase in the area of contact of heat carriers, due to a special internal design capable of more uniform heat transfer, due to a non-standard layout of the recuperator unit to avoid freezing and “defrosting” of condensate at the heat transfer surface. Application in many types of buildings, as there is minimal mixing of supply and exhaust air. The operation of the ventilation system is regulated by automation, in order to obtain a more comfortable microclimate in the room.Conclusions. The new design acquires an increased efficiency compared to analogues.

The article presents a numerical simulation of nonstationary heat conduction problems under complex heat transfer, which includes such heat transfer mechanisms as heat conduction, convection, and radiation. The Stefan-Boltzmann law describes the resulting heat transfer by radiation between two bodies, where the heat transfer coefficient is a function of the body surface temperature. An algorithm and software for solving the heat conduction problem using the finite element method were developed, and the influence of external impacts on the temperature field distribution in the vicinity of an insulated circular hole in the center of the body was studied. The temperature fields were investigated for various boundary conditions in the hole of the plate and the corresponding isotherms were given.

Heating of oil and oil products is widely used to reduce energy losses during transportation. The flow in the annular space of the heat exchanger is complex and depends on many factors. The use of thin tubes in helicoid-type heat exchangers makes it necessary to take into account the transition of the flow regime from laminar to turbulent. The semi-empirical turbulence models traditionally used in numerical calculations do not take into account the laminar-turbulent transition. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant at its outlet in the case of a strong dependence of oil viscosity on temperature, taking into account the possibility of a laminar-turbulent transition. Oil is considered as a heated coolant, and water is considered as a heating component. The novelty of the developed approach lies in the application of the turbulence model, which takes into account the laminarturbulent transition, to the calculation of helicoid-type heat exchangers. For numerical simulation, the Reynolds-averaged Navier–Stokes equations are used which are closed using γ–Reθt turbulence model that takes into account the laminarturbulent transition. The results of numerical calculations are compared with the data obtained on the basis of the logmean temperature difference method at constant and variable viscosity. In the case of variable oil viscosity, a transition from the laminar flow regime to the turbulent one is manifested which has a significant effect on the effective length of the heat exchanger. The results of numerical calculations can be useful in designing helicoid-type heat exchangers.

The purpose of this work is to create a compact supercharger to provide circulation of protective gas medium in a closed circuit. It was proposed to use a thermomechanical compressor to achieve this purpose. The operating principle of such devices is to change cyclically the temperature of the working medium in contact with warm and cold sources. Heating and cooling are carried out sequentially, pushing a part of gas through the regenerator by means of a displacer. The energy consumption for piston displacement is lower by an order of magnitude than that in conventional compressors. This makes it possible to use a seamless displacer movement mechanism. There can be two designs, both with one of the heat carriers close to ambient temperature. In a high-temperature thermomechanical compressor, the temperature is usually does not exceed 800 K. In the second type compressor, by reducing the absolute temperature of the cold "source" it is possible to achieve a high degree of compression at a relatively small temperature difference. The most significant result of the work is the design of the small-sized thermos-compressor that ensures a moderate degree of gas compression. The significance of the achieved results is shown in the compactness and tightness of the prototype for the use as an alternative to traditional machines in the field of inert gases production. The proposed technical solutions were tested during bench tests of the thermomechanical compressor. The experimental dependences were obtained of the flow rate characteristics on temperature mode, discharge pressure and cycle period.

The introduction of new types of heat exchangers with phase transitions and the solution of problems of optimizing the design and operational characteristics are a priority within the framework of the energy saving program. Known methods for calculating the heat-hydrodynamic parameters of the flow of refrigerants often do not take into account the specifics of boiling processes at low temperatures as well as in channels with a small flow area. This paper presents the results of modeling heat transfer during the boiling of refrigerants in the channels of evaporators of heat and cold energy complexes, taking into account the true flow parameters. The proposed mathematical model of the boiling of the working substance in channels of various shapes is based on the true flow parameters which imply knowledge of the channel cross-sectional areas occupied by each of the phases. The value of the true volumetric steam content provides the most correct modeling of two-phase flows in a wide range of regime and geometric parameters. The paper uses the equations of material and heat balance in combination with the equation of heat transfer from the environment to the boiling refrigerant. The map of flow regimes is used as an empirical component. A program has been developed for calculating the proposed system of equations which is solved iteratively at each time step using the finite volume method. Comparison of calculation results with experimental data on models of round and rectangular channels with intracanal boiling of refrigerants at positive and negative saturation temperatures is performed. It is shown that the calculation error does not exceed 10 % for a round and 20 % for a rectangular flow section. The verification results showed the possibility of using the model in the framework of engineering calculations. The proposed mathematical model can be used as the basis for the calculation programs for existing evaporators and for the creation of new types of heat exchangers with in-tube boiling of the working substance. The proposed method allows optimizing both geometric and thermal-hydrodynamic parameters.

The mathematical model to inspect the effects of changeable thermo-physical properties such as thermal conduction, slip effects and viscosity on Maxwellian nanofluid is proposed. The thermal conductivity increases rapidly due to presence of nanoparticles such as metals, carbides, oxides etc. in base fluid. The flow occurs from the stagnated point pass a stretched sheet with slipped conditions. The characteristics of the Brownian motion as well as the thermophoresis processes are also taken into consideration. By means of similarity transformations, the ODEs are reduced from the equations influencing the fluid flow. A built-in solver of MATLAB namely bvp4c which is a collocation formula implementing the Lobatto IIIa finite differences numerical method is applied to solve these transformed equations numerically. The graphs of the numerical outcomes representing impacts of variations in different parameters on the fluid movement, transfer of heat along with mass are analyzed. This investigation leads to an important aspect that as the thermal conductivity in the flow is intensified, the temperature of the fluid reduces with high aggregation of the nanoparticles near the sheet’s surface. Also, the rates of heat and mass transferral depletes due to the relaxation of Maxwellian fluid. Furthermore, the effectiveness of the present numerical computations is determined by carrying out comparisons of heat and mass transferred rates against the previous analytical results for several values of thermophoresis and Prandtl parameters. The effectiveness of its outcomes can be applied in nanoscience technology and polymeric industries for their developments.

Copyright of Renewable Energy / Vidnovluvana Energetyka is the property of Institute of Renewable Energy of NAS of Ukraine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Today, one of the most significant and widely used engineering fields is heat transfer science. Saving energy and increasing efficiency are crucial given the need for energy management. Numerous sectors, including the cooling of machinery in power plants, the car industry, electronic equipment, and heat exchangers, heavily rely on fluid heat transfer. Improved design and functionality of thermal systems are made possible by increased heat transfer rate by fluids. This study presents the production, characteristics, and potential uses of PEG/MgO/SiC-H2O nanofluids as superior heat transfer media. Results indicate that when the quantity of MgO/SiC nanoparticles increased, the melting time reduced. Additionally, when the MgO/SiC NP concentration increased from 3 to 12 weight percent after 15 minutes, the reduction in melting time reached 65.5%. Additionally, when the concentration of MgO/SiC NPs was increased from 3 weight percent to 12 weight percent at photon wavelength (λ=400 nm), the electrical conductivity of PEG/MgO/SiC-H2O nanofluids increased by about 30.6%. At the same time, the absorbance increased by about 66.4% and the transmittance decreased by 58.8%.

To solve the problem of increasing the energy efficiency of thermal networks with heat pipelines located in impassable channels, a schematic and structural solution for the rational utilization of thermal waste generated during the transport of thermal energy has been developed. Due to the complexity of creating a full-scale experimental installation, a virtual experimental installation created by means of the Ansys software package was used in the study, on which an active numerical experiment was performed. Regression equations have been obtained for calculating the intensity of heat transfer from pipelines and channel enclosing structures with a given change in the size, length of channels and pipelines for various outdoor and ground temperatures characteristic of the heating and inter-heating periods. Statistical analysis, verification and validation of the obtained regression correlations were carried out, two-dimensional hypersurface crossections were obtained in the studied range of controlled factors. The results of numerical simulation of the operating modes of forced ventilation of impassable channels of heating mains with determination of the density of heat flows from the ground and mains water pipelines, air flow and the corresponding exhaust fan capacities have been presented. The following conditions in this case were accepted: the air flow rate is not higher than 8 m/s, the length of the heat pipeline section ensures the air temperature at the outlet of the channel at which there is no increase in heat losses from mains water pipelines to the ground under normal operating conditions of heating networks. The energy efficiency of heat utilization dissipated by mains water pipelines as well as ground cooling in impassable heating mains channels was investigated by intensifying their ventilation and using heat pump equipment at the end points of the channels for heating mains water, depending on the geometric characteristics of the heating mains section, air temperature, soil and mains water installations at central heating points or directly at heat sources. The potential of energy saving for district heating systems with various types of heat sources and the combined power system during the utilization of heat flows from the ground and heat pipelines laid in impassable channels has been identified. On the basis of the energy-saving potential, a technical and economic assessment was carried out and the conditions for the economic feasibility of implementing the proposed technical solution were determined.

Background. It is known that during the drop condensation of hydrocarbon vapors, the heat exchange between the vapor and the wall is 5-10 times greater than during film condensation. Therefore, the intensification of film condensation is the task of an efficient process of condensation of hydrocarbon vapors in oil refining. Purpose. To intensify the process of condensation of hydrocarbon vapors with a decrease in film condensation due to the vortex flow and increase the thermal efficiency of the process. Methodology. Technological parameters were measured, using instrumentation, processes of condensation of hydrocarbon vapors. Originality. For the first time, the degree of intensification of the condensation of hydrocarbon vapors in the experimental apparatus due to the circulating supply has been established. Findings. The circulating supply of steam in the apparatus leads to an increase in the heat transfer coefficient by 6.7%, and the amount of heat transferred by 7.8%, which leads to a decrease in the design dimensions, weight and working surface of the condensers. [ABSTRACT FROM AUTHOR]

Introduction. The study of heat exchange in cooled combustion chambers and the influence of various factors on its intensity is a complex and relevant task. The analysis of theoretical and experimental data on heat exchange in combustion chambers of various plants has proven that current methods fail to take into account features of heat exchange in furnaces, having small geometric dimensions and, therefore, they cannot be used for their thermal calculation.Materials and methods. The author presents the experiments and the results of their generalization performed using the criterial equation. Generalization results are of great importance for analyzing heat transfer processes and the thermal analysis of cooled combustion chambers of small capacity heat generators. The contribution of radiative and convective components to complex heat exchange processes in combustion chambers of low-capacity boilers is evaluated using this generalized dependence. The author has identified qualitative and quantitative dependence of integral radiative and convective heat exchange on the main factors of operation of small combustion chambers.Results. The author has obtained generalizing criterial dependence that makes it possible to evaluate the contribution of radiative and convective components to complex heat exchange in combustion chambers of low-capacity boilers.Conclusions.The generalized criterial dependence, obtained by the author, can be used to identify the qualitative and quantitative dependence of integral radiative and convective heat transfer on the main geometric, physical and performance factors of operation of small capacity furnace chambers. The assessment of reliability of the experimental data, obtained by the author, has shown that the value of the limiting mean square error of determining the value of integral heat transfer Kh.t will be 3.24 %. For all experiments, the deviation of the calculated data from the experimental results with a 95 % probability does not go beyond the confidence interval of ±9.52 %.

Introduction. A set of calculations validating the conditions of limit states is to accompany the design of buildings and structures. Calculations of standard and non-standard combinations of loads and impacts are performed. Special loads include temperature effects from explosions and fires. Such effects greatly reduce the bearing capacity of metal structures. To protect metal structures from temperature effects, optimally selected fire proofing materials (varnishes, paints, various types of cladding) should be used. Numerical calculation methods allow analyzing the performance of building structures, exposed to temperature effects, and help select the necessary characteristics and thicknesses of fire proofing materials.Materials and methods.A metal hinged beam is used to analyze the influence of fire proofing, or lining made of fire-resistant gypsum sheets (FRGSh). Analytical and numerical methods of calculations were used to obtain the fire resistance limit of beams with cladding. The analytical method is based on the laboratory studies of fire resistance, as a result of which nomograms were obtained. The numerical method is implemented by Lira 10.12 software package.Results. Analytical and numerical methods were used to identify the fire-resistance limits for a beam that had FRGSh cladding. Temperature field mosaics in the elements along the thickness of the structure, as well as graphs of temperature changes and temperature fields in time were obtained using the numerical method. The obtained results showed good convergence.Conclusions. The use of numerical methods makes it possible to quickly and optimally select the required thickness of fire proofing for a steel structure. Calculation results are highly dependent on the characteristics of the materials in question, as well as the heat transfer environment.

Relevance. At present, there are no general methods for determining temperature of an undisturbed formation from thermometry data in non-equilibrium wells. When drilling a well, the natural temperature distribution in the formation surrounding the well changes significantly and it takes a considerable time to wait for its restoration. This process can last up to a number of months and even more in deep wells. Therefore, the undisturbed formation can only be directly measured in a small number of shut-in wells. Modeling the temperature recovery process in wells after drilling is the only way to predict the undisturbed formation temperature, required to the equilibrium temperature gradient and heat flux density determination in order to provide necessary initial data for basin and hydrocarbon system modeling. Object: drilling wells and preliminary flushed wells before temperature studies. Well diameter changes after drilling due to the presence of cavities. The cavities affect the temperature distribution after the well casing, since the volume of injected cement in these intervals is increasing. Purpose of the research is to determine the temperature field disturbance in the depth intervals with a changed well diameter due to the cavitation process, as well as the cement sheath effect on the temperature distributions. Results. The influence of cavity size (height and depth) on the temperature field in the well was studied. The authors developed the mathematical model describing flushing fluid movement in the well and taking into account changes in well diameter. It was shown that the temperature field opposite the cave intervals is strongly disturbed in an uncased well. It was revealed that with an increase in the flow rate of the flushing fluid the temperature field is most strongly disturbed opposite the bottom of the cavity interval.

The increase in the thermal protection level of the existing buildings enclosing structures, due to the need to comply with the current norms of building heat engineering requirements, leads to increasing in the part of heat losses in the thermal balance of a building due to infiltration and exhaust ventilation operation. After exhaustion of the possibilities for the implementation of technical measures to reduce energy costs by changing in volumetric planning solutions and insulating building envelopes further decreasing heat consumption level should be associated with the use of the secondary and renewable resources potential. The paper presents the results of assessing the technical and economic feasibility of using the exhaust air thermal potential for heating the supply air in the forced supply-and-exhaust ventilation system of a building taking as a low-capacity unit as an example. For a counterflow air-to-air recuperative type heat utilizer finned with ribbed heat pipes in the form of a plurality of continuous sheets, the influence of changes in the physical properties of the exhaust air during the phase transition of the water vapor contained in it into a liquid state on the heat exchanger-utilizer performance and characteristics of its efficiency has been established. The conditions of heat exchange are determined (without condensate, with condensate in the part of the heat exchanger-utilizer, with condensate in the entire heat exchanger-utilizer and with the risk of icing) in the supply air temperature range from (–26) to (+8) °C for three variants of its operation with a balance of the nominal amount of exhaust and supply air and with two variants of imbalance. Variants with imbalances have been investigated in order to find possible combinations of supply and exhaust air temperatures, at which there would be no phase transition of water vapor in the exhaust air flow to the liquid state in the entire volume of the heat utilizer, which would eliminate the need for measures to collect and remove condensate and preventing it from freezing.

A comparative analysis of the methods of approximate thermal calculation of the superheated steam condenser of the steam compression heat pump of the heat supply system is presented. The working substance of the heat pump and the condensing steam is the refrigerant R410a. When the single-zone method is applied, the condenser is calculated by one area with the inclusion of the heat of overheating in the heat of condensation and the use of the overheating coefficient. The two-zone method assumes the calculation of the condenser in two separate areas, viz. the cooling of superheated steam and its actual condensation. The approbation was carried out during a numerical study of a condenser of a low-temperature heat pump system for heating and hot water supply, with a heat exchange surface in the form of a spiral coil pipe in a pipe immersed in a heated liquid. In the first approach, the flow rate and temperature of the heated water are limited by the saturation temperature of the condensing refrigerant, regardless of the flow pattern of the working media. The method of two-zone calculation of the superheated steam condenser with a counter-current or cross-counter-current flow scheme of working media makes it possible to obtain real results of the temperature of the heated water that exceeds the temperature of the saturated refrigerant vapor, taking into account the flow rate of the heated water. In this case, the wall temperature in the cooling area is higher than the saturation temperature, and during condensation it is lower, which further confirms the adequacy of the presented technique. The use of a two-zone technique with a separate averaging of the physical properties of the working media in the areas of superheated steam and condensation cooling, as well as temperature pressures, provides a more accurate value of the heat exchange surface, which in the case under consideration is reduced to 20%. Based on the conducted studies, it is recommended to use a two-zone technique that makes it possible to obtain reliable data on the parameters of the superheated steam condenser.

THE PURPOSE. To carry out mathematical modeling of interrelated physicochemical processes in radiation chambers of tubular furnaces of pyrolysis of hydrocarbons. Perform numerical calculations of heat and mass transfer in the furnace furnace chamber with a multi-tiered arrangement of wall burners on the side lined walls.METHODS. Using our own package of applied programs based on the numerical solution of a system of differential equations of energy conservation and equations of radiation gas dynamics, the fields of velocities and temperatures of natural gas combustion products in the radiation chamber of a hydrocarbon pyrolysis tubular furnace are calculated. Interrelated processes of natural gas combustion, radiant-convective heat transfer, and turbulent flow of flue gases take place in the radiation chamber. These processes are modeled by two-dimensional equations of the combustion model, energy transfer by radiation, and equations of motion. In the side walls of the radiation chamber on both sides in eight horizontal tiers there are wall burners in the amount of 128 pieces. Combustion products emerging from the nozzles of these burners create complex velocity and temperature fields in the chamber volume. Due to the radiation of flue gases, the smallest soot particles and hot lined walls of the radiation chamber, heat flows are formed to the tubular screen, where hydrocarbons are pyrolyzed to produce ethylene.RESULTS. As a result of calculations, the velocity fields, the temperature in the volume of the radiation chamber and the concentration of the main components of the combustion products were obtained. Local values of surface densities of radiant heat fluxes to reaction pipes for methane and propane pyrolysis furnaces are calculated. Comparisons of some of the results obtained with the readings of the devices of existing technological installations are carried out.CONCLUSION. Calculations show that the developed software package makes it possible to obtain realistic values of local velocities and temperatures in the radiation chambers of tube furnaces, surface densities of convective and radiant heat fluxes to boundary surfaces, and other thermal and gas-dynamic parameters in the furnace volume. With a multi-row arrangement of a large number of wall burners of low thermal power, a complex field of temperature and velocities of combustion products in the furnace volume is formed on the side walls of the radiation chamber of the furnace. At the same time, this arrangement of the burners ensures a fairly uniform distribution of heat flows over the surface of the tubular screen of the hydrocarbon pyrolysis furnace.

THE PURPOSE. Improving the energy efficiency of open cell foam materials with different geometries (SC, BCC, FCC, DEM) and with different medium porosities (ε=0.7; ε=0.75; ε=0.8; ε=0.85; ε=0.9; ε=0.95) by numerical simulation. To determine the influence of the geometry and porosity of an open cell foam material on the values of pressure drop, heat flux and energy efficiency factor.METHODS .Numerical simulation was carried out using the ANSYS Fluent 19.2 software package. Geometric models of porous structures are sets of intersecting spheres with different packing structures: periodic Simple Cubic packing (SC), Face Centered Cubic packing (FCC), Body Centered Cubic packing (BCC), and random structure generated by the discrete element method (DEM).The calculations were carried out at the following air flow velocities: 0.01; 0.05; 0.25; 0.5; 0.75; 1; 1.25 m/s.RESULTS. Atair flow velocities of 0.01 m/s and 0.05 m/s, all the studied structures show approximately the same heat flux. With porosity values ε=0.75; ε=0.8; ε=0.85 the highest values of heat flow were shown by the FCC structure, with porosity ε=0.7; ε=0.9; ε=0.95 the BCC structure had the highest heat flux. This is explained by the fact that, at the corresponding porosity values, the FCC or BCC structure had the largest surface area, which provided the largest heat flux. With the porosities of media ε=0.7 and ε=0.75, the BCC and FCC cell packages show a high pressure drop. With the porosities of media ε=0.8 and ε=0.85, the highest pressure drop corresponds to FCC cell packing, and for porosities ε=0.9 and ε=0.95, to BCC cell packing.CONCLUSION. With equal high porosity, the BCC cell packing provides a higher value of heat flux than the FCC structure. The SC package has the lowest heat flux values for all studied porosities. The SC package also has the lowest pressure drop values and therefore the highest energy efficiency values.

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The relevance of the study follows from the high demand for artificial freezing of soils in sinking vertical mine shafts. Analysis of methods for calculating heat transfer between brine in freezing columns and surrounding soil makes it possible to further improve the methods for calculating heat transfer coefficients. The research results will be useful for designing freezing systems in shaft construction. The main aim of the research is to analyze the existing methods for calculating heat transfer between the coolant in the freezing column and the surrounding rocks, to determine the main ways to further improve the methods for calculating heat transfer in conditions of coaxial freezing columns Objects: the system «brine – freezing pipe – frozen soil». Methods: comparative analysis of existing methods for calculating heat transfer, numerical simulation in the Ansys Fluent software package. Results. The authors have carried out the comparative analysis of the existing approaches and methods for calculating the heat transfer coefficient through the wall of the freezing pipe between the brine (coolant) moving along it and the frozen soil. The paper describes the reasons for discrepancy between the results when using various methods for calculating heat transfer. The authors have carried out the comparative analysis of the heat transfer coefficients obtained by various calculation methods, as well as as a result of numerical three-dimensional modeling of the brine flow. The drawbacks of the existing methods for calculating heat transfer are shown and the main ways of further improving the methods for calculating heat transfer under conditions of coaxial freezing columns are determined: taking into account heat transfer between the forward and reverse brine flows in the freezing columns, analyzing the effect of transient velocity and temperature fields in the reverse brine flow at the initial section of the freezing column (near the column shoe), analysis of the sensitivity of the value of the heat transfer coefficient to deviation from the alignment of the supply and freezing pipes.

It is necessary to develop quantitative methods to assess the formation of thermal burns in the morphological parts of coniferous trees. The purpose of the study is mathematical modeling of heat transfer in the layered structure of a coniferous tree branch under the influence of a forest fire front. The heat propagation in the «branch — needles — flame zone» system is described by a system of non-stationary differential equations of heat conduction with the corresponding initial and boundary conditions. As an object of research, a digital model of a branch of a coniferous tree for various species, namely, pine, larch and fir, was used. Temperature distributions are obtained for different variants of the branch structure and conditions of the impact of the forest fire front. Conclusions are made about the need for further modernization of the mathematical model. The developed model is the basis for creating software tools for specialized geographic information systems.

The object of the study is a multilayer foiled material obtained from the waste of the textile industry. The aim of the work is to develop a method for determining the basic thermophysical properties of nonwovens. A method for finding the coefficients of thermal conductivity and thermal conductivity of non-woven fabrics made from textile waste is proposed. The article, describes experimental studies and discusses the dependences of changes in the thermophysical properties of nonwovens under the influence of a stationary heat flow on them. The developed installation and methodology allow us to quickly determine the thermophysical properties of foiled nonwovens, in comparison with materials that do not have a protective coating in the form of aluminum foil. Целью работы является разработка метода для определения основных теплофизических свойств нетканых материалов. Предложена методика нахождения коэффициентов теплопроводности и температуро-проводности нетканых полотен, произведенных из отходов текстильного производства. В статье произведены экспериментальные исследования и установлены зависимости изменения теплофизических свойств нетканых материалов в условиях воздействия на них стационарного теплового потока. Разработанная установка и методика позволяют оперативно определять теплофизические свойства фольгированных нетканых материалов, в сравнении с материалами, не имеющими защитного покрытия в виде алюминиевой фольги.

Deviations of the РТ parameters from the background values, corresponding to the lithostatic pressure and the standard geotherm characteristic of the neighboring crustal blocks of the Yenisei Ridge, were recorded by geothermobarometry in the zones of dislocation metamorphism of the Yenisei regional shear zone (Eastern Siberia). To explain the reason for large deviations from metamorphic conditions for shear and collision, we worked out 3D and 2D thermomechanical numerical models. The paper presents two- and three-dimensional models of dissipative heating during friction and visco-plastic deformations. The modelling results are compared with geological observations on the metamorphic grade and the scale of deformations of the Yenisei regional shear zone. A detailed consideration is being given to the ratio of heat released during friction at the contact of shear fault blocks, or during viscous deformations of the rheologically layered zone of tectonic flow and blastomylonitization. Estimates of the magnitude of dissipative heating are obtained for typical parameters of shear zones. The model of viscous deformation of a shear zone of finite width, taking into account the rheological layering of the crust, predicts dissipative heating by 200–310 °C at strain rates of 2–4 cm/year. The model of obduction of the tectonic plate with a thrusting velocity of 5 cm/year yields estimates of frictional heating of rocks at the contact of blocks no higher than 130–190 °C. The characteristic time period of the stationary dissipative regime formation is 6–8 million years. Dissipative heating could be a heat source for the metamorphic complexes of the Yenisei regional shear zone, though melting conditions of metapelite were not attained.

The paper presents the influence analysis of such uncertainty factors as the heat transfer coefficient calculation method and the working chamber wall temperature on the mathematical modeling of the ammonia compression in a reciprocating compressor stage during the condensation of ammonia vapors. The mathematical model is based on the equation of the first law of thermodynamics for bodies with variable mass, the equation of state for real gases, the Clausius–Clapeyron and Newton–Richman equations. When determining the heat transfer coefficient value, several well-known dependencies for calculating these coefficients for dropwise and filmwise condensation have been considered. The calculation data shows that the instantaneous values of the ammonia pressure and temperature, as well as of the dryness fraction during compression in the wet steam region, significantly depends on the chosen method for calculating the heat transfer coefficient. Moreover, the walls temperature value of the compressor working chamber, where the compression occurs, has a considerable impact on the process under discussion. They are the determining factors and require special attention when the ammonia compression process is mathematically modelled in a reciprocating compressor stage, taking into account its vapors condensation.

The relevance of the study is caused by the decrease in thermal energy consumption to ensure the thermal conditions of local working zones in industrial premises, the characteristic dimensions of which significantly (many times) exceed these zone dimensions. The problems of energy conservation have been relevant for many decades for a number of objective reasons. However, so far there is no occasion to conclude that most of the issues arising in the production and social spheres have been solved. The well-known method of local «heat supply» of a relatively small workplace with the use of gas infrared emitters until recently has been little used due to the lack of a scientific and technical base that provides experimental design work to create systems for ensuring the thermal conditions of local workplaces based on gas infrared emitters. Aim: analysis of the energy efficiency of gas infrared emitters as the main elements of systems for ensuring the thermal conditions of local working zones. Objects: a large room heated by a gas infrared emitter. Methods: experimental measurements of floor surface temperatures with chromel–alumel type thermocouples with a junction thickness of 0,08 mm and data recording using the NI 9214 temperature measurement module from National Instruments; mathematical modeling of heat transfer processes in a multilayer floor. Results. The article presents the results of experimental and theoretical studies carried out to assess the effectiveness of using such systems. The experiments were carried out in a special box that reproduces the conditions for supplying heat from the emitter to a small workplace. The floor surface temperature was measured at ten characteristic points during typical averaged power emitter operation. The experimental results were used as boundary conditions at the «air – box floor surface» interface when solving heat conduction problems. Based on the results of experimental and theoretical studies, the advantages (in comparison with traditional convective heating systems of even small-sized industrial premises) of systems based on gas infrared emitters for ensuring the thermal conditions of local working zones are substantiated. The essence of these advantages lies in the fact that when using emitters, the routine thermal conditions is provided without energy consumption for heating the enclosing structures and air outside the working area (which can be ten times smaller in terms of the entire industrial premise volume).

The article is devoted to the study and development of a mathematical model of the process of electrification of textile materials in the system "man - clothing - environment" in hot climatic conditions. The phenomenon of static electrification, which occurs in the processes of manufacturing textile materials and products from them, as well as during the operation of finished products, leads to a decrease in the quality of products, causes inconvenience in work, and when an electric discharge occurs, it poses a threat to human life. Such interactions of elements in the "person - clothing - environment" system such as friction, compression, tension, shear increase the contact area of two media, and depending on the rate of these processes, they enhance or weaken metabolic processes, which contributes to an increase in the maximum static charge generated on contacting surfaces. temperature values for special clothing of limited length at the nodal points. At the same time, the number of nodal points is 1601, the number of connected elements is 800. In the area of temperature distribution along the length of the garment, in four different versions, it was found that in the I – version , in the II – version , in the III – version , in the IV – version , in the V – version , in the VI - version, the length of the clothes in this area increased by 10% compared to the length of the clothes in the II – version.

It is necessary to develop quantitative methods to assess the formation of thermal burns in the morphological parts of coniferous trees. The purpose of the study can be formulated as follows: mathematical modeling of heat transfer in the layered structure of a coniferous tree branch under the influence of a forest fire front. The heat propagation in the “branch-needles-flame zone” system is described by a system of non-stationary differential equations of heat conduction with the corresponding initial and boundary conditions. As an object of research, a digital model of a branch of a coniferous tree for various species, namely, pine, larch and fir, was used. Temperature distributions are obtained for different variants of the branch structure and conditions of the impact of the forest fire front. Conclusions are made about the need for further modernization of the mathematical model. The developed model is the basis for creating software tools for specialized geographic information systems.

The numerical simulation of turbulent flow and heat transfer, when air moves around a thermal manikin sitting in a model room with mixing ventilation, has been carried out. The calculations were performed on the basis of the RANS approach using the standard k-ε turbulence model. The buoyancy effects were described in the Boussinesq approximation. The obtained calculated data were close to the experimental ones, although there were local differences in the temperature distribution near the surface of the room walls. The impossibility of correct determination of the integral heat removal from the surface of the body without taking into account the radiation heat transfer was established. Along with studies in the ventilation regime with predominant forced convection, corresponding to the experiment, the characteristics of the flow and heat transfer in the free convection regime were analyzed, where the flow structure being caused by an intensive thermal plume forming above the manikin, and the temperature field being stratified in height.

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Background. The study of heat exchange processes in printed circuit assemblies is a fundamental problem for ensuring a high level of reliability and performance of electronic equipment and complex systems in general. Temperature control, obtaining reliable information about overheating temperatures of electronic components, identifying critically unstable elements and developing new technological methods for heat removal – these are the goals that can be achieved to ensure a high level of reliability of modern electronic equipment. Materials and methods. The relevance of the problem posed in the work is due to the widespread use in modern electronic equipment of microelectronic components that have direct contact with the surface of the printed circuit board, which in turn leads to a change in the nature of the temperature distribution, and in combination with the use of multilayer printed circuit boards, completely redefines the existing methods for studying and analyzing thermal processes in printing units. Results and conclusions. The work is aimed at studying heat transfer processes in printed circuit assemblies, and the scientific novelty lies in the development of a new method for predicting the reliability of electronic equipment by measuring and analyzing the thermal regime of printed circuit assemblies, taking into account not only the printed circuit board and components, but also the influence of the topology of printed conductors on its thermal regime , which together form a complex system for measurement and analysis.

Copyright of Refrigeration Engineering & Technology is the property of Odesa National University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Problems of Friction & Wear is the property of National Aviation University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper presents an analytical study of one-dimensional fluxes of ballistic quasiparticles in the presence of scattering centers. Such a situation can be realized at very low temperatures or systems of very small sizes – nanostructures. To describe such a situation, the approach of heat transfer by radiation, which goes back to Casimir, is used, in which the interaction of phonons with image boundaries is taken into account, or, for example, the Landauer approach, where the probability of phonon transition from the initial state to the final state is introduced. At the same time, the intermediate regime, the mean free path of phonons due to their interaction with each other, is comparable to the size of the samples; to this day, it remains a rather difficult problem for a theoretical or numerical solution. In this work, we propose the probabilistic approach in the Landauer model to describe heat transfer in the one-dimensional ballistic motion of quasiparticles. Within the framework of the theory of random walks, a model of successive scattering centers is considered. An explicit analytical expression is obtained for the dependence of the flux of quasiparticles on the probability of scattering and the number of scattering centers. In order to explain the physical sense of the obtained result the comparison with the result of iterative approach is made. As well the results are used for description of the problem of the heat flux in multilayered structures, in which one should take into account not only the thermal resistance inside the layers, but also the Kapitsa resistance between the layers. The practical application of the obtained results to one-dimensional nanostructures and to quasi-one-dimensional heat-conducting systems is discussed, various limiting cases are considered and a comparison with experimental data is made.

The paper presents the simulation results of heat transfer in single-crystal lithium niobate (LiNbO3) in the form of cylinder of diameter mm and height mm in interaction with continuous-wave laser radiation with the output power of W and the wavelength of nm. The density of the LiNbO3 crystal is kg/m3; the thermal conductivity along the [001] direction is W/(m×K); the thermal conductivity in the (001) plane is W/(m×K); the specific heat at constant pressure is J/(kg×K); the absorption coefficient is %/cm @ 1064 nm. The laser beam propagates along the optical axis of the crystal. The laser beam intensity profile is represented as a Gaussian function, and the absorption of laser radiation of the single-crystal lithium niobate is described by Beer-Lambert’s law. The numerical solution of the non-stationary heat conduction problem is obtained by meshless scheme using anisotropic radial basis functions. The time interval of the non-stationary boundary-value problem is 2 h 30 min. The results of numerical calculations of the temperature distribution inside and on the surface of the single-crystal lithium niobate at times s are presented. The time required to achieve the steady-state heating mode of the LiNbO3 crystal, as well as its temperature range over the entire time interval, have been determined. The accuracy of the approximate solution of the boundary-value problem at the n-th iteration is estimated by the value of the norm of relative residual . The results of the numerical solution of the non-stationary heat conduction problem obtained by meshless method show its high efficiency even at a small number of interpolation nodes.

The relevance of the research is caused by the need to reduce the air temperature during mining operations in dead-end workings associated with the release of a large amount of heat. Development of ways to normalize the thermodynamic parameters of mine air in the faces based on the construction of predictive mathematical models of change of the thermal regime is a necessary condition for safety in the mining industry. The aim of the research is to obtain dependences for determining the rate of air temperature increase in a dead-end mine at known values of the intensity of heat release and its removal by a ventilation jet. Objects: dead-end workings and the surrounding rock mass. Methods: solution of the problem of non-stationary heat transfer of mine air and rock mass in the conjugate formulation using Laplace transformations; safety assessment on the gas factor of intensification of heat removal from the production by increasing the air supply to the bottom using recirculation. Results. The authors have analyzed the problem of heat removal, released during the operation of mining equipment in a confined space of mine workings. It is shown that heat absorption by the rock mass and its removal due to ventilation may not be enough to prevent excessive overheating of the air. A mathematical model of the conjugate heat exchange of air and rock is developed, which allows predicting the temperature increase over time depending on the length of production and the total intensity of heat release in it. It is established that heat exchange lasting several hours can be modeled in the approximation of small times, which greatly simplifies the calculated dependences. The calculation of the dynamics of the thermal regime under a set of physical parameters characteristic of mine conditions of the problem, the results of which were the basis of the approximation made and confirmed the danger of a rapid increase in air temperature with insufficient intensity of heat removal from the workings of the ventilation jet. It is proved that if additional heat removal is necessary, it is possible to use traction sources with a large flow rate and air recirculation, without fear of increasing gas content in the bottom hole.

The task of increasing heat transfer of hydrocarbon fuel in the channels of cooling systems of liquid rocket engines is a matter of current interest. The article discusses the results of developing a mathematical model of an engine cooling system operating on super-circulation of fuel between the tank and the nozzle. The model makes it possible to determine the conditions under which the ratio of kerosene circulation in the nozzle cooling circuit would ensure that the selected material is used as the nozzle wall material, to find the minimum amount of kerosene in the tank required for cooling the nozzle by the proposed method.

The problem of determination of temperature fields in the flow and efficiency of heat exchangers with intensification by metal chaotic packings is considered. Results of experimental studies of the heating of industrial oil with hot water in a "pipe-in-pipe" heat exchanger, where a chaotic packing of nominal size 6 mm is placed in the internal pipe, are presented. The packing, due to turbulence in the flow of oil, provides transition from the laminar to the turbulent regime and a significant increase in heat transfer coefficient (by 15-20 times). For calculating temperature profiles in channels, a cell model of the flow structure is written, where the main parameters are thermal number of transfer units and number of complete mixing cells. Expressions are given for calculating these parameters in pipes with chaotic packings. Results of calculating temperature profiles for various flowrates of the heated oil are presented and satisfactory agreement with experimental data is shown. The calculation of temperature fields makes it possible to take into account a change in thermophysical properties of flows along the length of the channels, which is especially important for hydrocarbon mixtures with high viscosity and large Prandtl numbers. The presented mathematical model allows to take into account the structure of heat carrier flows in apparatus with intensifiers and to calculate thermal efficiency of the processes of heating and cooling the media.