Conditions Of Heat Exchange Research Articles

Thermal Runaway Behaviors and Kinetics of NCM Lithium-Ion Batteries at Different Heat Dissipation Conditions

The lithium-ion battery (LIB) thermal runaway is triggered by the exothermic reactions between electrode materials and other active substances such as electrolytes. In this study, the effects of ambient temperature and heat transfer coefficient on the thermal responses and chemical kinetic features of LiNi1/3Co1/3/Mn1/3O2/graphite battery thermal runaway at high-temperature abuse conditions are investigated using a validated 2D axisymmetric model. With varied heat transfer coefficients of the LIB, the corresponding runaway, critical, and safety operation zones at different ambient temperatures are quantitatively distinguished. The results reveal that, with increased heat transfer coefficient, the critical ambient temperature, T c, triggering thermal runaway increases. However, T c almost remains 430 K when the heat transfer coefficient is higher than 25 W/(m2K). Additionally, based on the thermal response of LIB, the ambient heat absorption stage, ambient heat dissipation stage, and dramatic heat release stage in thermal runaway are defined. It is found that a higher heat transfer coefficient efficiently causes a shorter ambient heat absorption stage, which is the primary reason for the reduced delay time for the thermal runaway. Further, kinetic analysis is conducted at different heat exchange conditions, and the correlation between LIB thermal responses and the heat release of side reactions in different operation zones is clarified. Specifically, the reactions between the electrolyte and negative/positive electrodes are the most exothermic and most influential of all side reactions, and their influence on the maximum temperatures and runaway delay times is promoted with an elevated heat transfer coefficient.

The nature of the frequency dependence of the adiabatic temperature change in Ni50Mn28Ga22-x(Cu, Zn)x Heusler alloys in cyclic magnetic fields

This study presents the results of direct measurements of the adiabatic temperature change (∆Tad) in Ni50Mn28Ga22−x(Cu, Zn)x (x = 0; 1,5) alloys in cyclic magnetic fields of 0.62 and 1.2 T at frequencies f= 1, 5, 10, and 20 Hz. The substitution of zinc and copper for the initial composition resulted in a decrease in ∆Tad and a stronger frequency dependence. The strong frequency dependence of ∆Tad near TC in the Ni50Mn28Ga22−x(Cu, Zn)x system is due to the inhomogeneous microstructure and the coexistence of martensite-austenite phases, which give rise to two simultaneously acting mechanisms. Firstly, the addition of Zn and Cu increases the coercive force HC, resulting in an increase in the viscosity coefficient. Secondly, an increase in the frequency of the cyclic magnetic field (i.e., an increase in the field sweep rate) leads to the same effect, increasing the viscosity coefficient. Which, in our opinion, is the reason for the frequency dependences of ∆Tad near TC. The study found that the specific cooling power (SCP) for the Ni50Mn28Ga22 sample in a cyclic magnetic field of 1.2 T increased with frequency, reaching 4.75 W/g at 20 Hz, which is 14.1 times greater than at 1 Hz. This suggests that, under conditions of sufficient heat exchange, the cooling efficiency of a magnetic refrigerator can be greatly improved by increasing the operating frequency.

Simplified Method for Determining Thermal Stresses during the Construction of Massive Monolithic Foundation Slabs

For massive monolithic foundation slabs, the problem of early cracking due to the intense heat release of concrete during the hardening process is relevant. The purpose of this article is to develop a simplified method for determining thermal stresses during the construction of massive monolithic foundation slabs. The proposed technique is based on the hypothesis of parabolic temperature distribution over the thickness of the structure at each moment of time. In addition to the parabolic distribution, the half-wave cosine distribution is also used. A hypothesis is also introduced about the same conditions of heat exchange with the environment on the lower and upper surfaces of the foundation. As a result, formulas are obtained that establish a direct relationship between thermal stresses and the temperature difference between the center and the surface. The solution to the test problem for the foundation slab is presented and compared with an alternative technique that does not use the hypothesis about the character of the temperature distribution over the thickness. Also, the inverse problem of determining the allowable temperature drop between the center and the surface of the structure is solved, at which the stresses on the upper surface at each moment of time will not exceed the tensile strength of concrete.

Numerical Simulation of the Effect of Heat Conductivity on Proton Exchange Membrane Fuel Cell Performance in Different Axis Directions

In this paper, the effect of changes in the thermal conductivity of porous electrodes in three coordinate directions on the capability of proton exchange membrane fuel cells is investigated on the basis of current density versus voltammetry curves, and the temperature distribution and water-carrying capacity distribution of the membrane. The results show that when the cell discharge voltage of the PEMFC is 0.3 V, the thermal conductivity in the Z-direction of the porous electrode has a greater effect on the performance of the PEMFC than in the other directions, with the thermal conductivity in the X- and Y-directions of the porous electrode having less than a 5% effect on the performance of the PEMFC, which can therefore be neglected. When the thermal conductivity of the porous electrode in the Z-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 5.78% and 5.87%, respectively, and when the thermal conductivity of the porous electrode in the X-direction of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), the performance of the PEMFC is improved by 2.09% and 2.89%, and the PEMFC performance is improved by 1.51% and 2.00% when the Y-direction thermal conductivity of the porous electrode of the PEMFC is 500 W/(m·K) and 1000 W/(m·K), respectively. The improvement in performance decreases with increasing thermal conductivity, because the thickness of the porous electrode is too thin. Since the side of the model is set to adiabatic heat exchange conditions, while the top and bottom surfaces are set to natural convection heat exchange conditions, the Z-direction thermal conductivity of the porous electrode plays the most important role in the temperature distribution of the PEMFC. The Z-direction thermal conductivity of the porous electrode causes the temperature distribution of the PEMFC assembly to be more uniform, and the Z-direction thermal conductivity of the porous electrode also causes the area of the high-water-content region on the proton exchange membrane to significantly increase.

Thermoelastic State of a Thermosensitive Half Space and a Thermosensitive Layer in Contact Under the Conditions of Complex Heat Exchange

We solve a nonstationary problem of heat conduction for a thermosensitive half space in contact with a thermosensitive layer under the conditions of complex heat exchange with the medium of constant temperature. To construct the solution, we use a numerical-analytic approach characterized by the application of a version of the method of successive approximations, linearizing parameters, the Laplace integral transformation, and its numerical inversion with the help of the Prudnikov formula adapted to the problems of heat conduction. The thermoelastic state of the outlined thermosensitive piecewise homogeneous structure is analyzed by applying the proposed algorithm.

MATHEMATICAL MODELING OF COMFORTABLE CONDITIONS OF CONVECTIVE HEAT EXCHANGE OF HUMANS AND ENVIRONMENT

Estimating environmental characteristics and determining comfortable conditions is a rather complex task that requires powerful mathematical and computer equipment. The purpose of the article is to build a mathematical model and determine the comfortable conditions of convective heat transfer of man and the environment by temperature in the city of Mykolaiv. The article “Mathematical modeling of comfortable conditions of convective heat exchange of humans and the environment” presents experimental studies of the evaluation of the comfortable conditions of convective heat exchange of the human body and the surrounding environment based on mathematical calculations allow to clearly outline the comfort zones in the cold period of the year. The basis of the research is the mathematical modeling of the comfortable conditions of the human body, which is based on the use of the developed algorithm, the basis of which is the synthesis of two software products. The ability to import data made a significant impact on the synthesized work of the programs, which made it possible to transfer the calculations without loss of content without loss of time. Optimal solutions identified during the creation of the algorithm allowed to create a method of mathematical modeling of the comfortable conditions of the human body. The heat exchange between the human body and the temperature of the atmospheric air is estimated. The graphical dependence of the change of convective heat exchange on the atmospheric air temperature is constructed. An approximation of the curve on the basis of which the derivative of the function is determined. The levels of comfort of convective heat exchange of man with the environment are presented. The optimal temperature conditions for the human body in the cold period of the year are substantiated. The normal temperature threshold is 1.5-0.5 °C, where the human body is in a comfortable state and there is moderate heat transfer. For the middle level, the temperature is determined in the range of 2.0-1.49 and 0.49-0 °C, where the increase in heat transfer begins due to the increase in atmospheric air temperature, which leads to sweating. Lowering the temperature, in turn, leads to heat release from the body to warm up.

Numerical Determination of the Nonsteady Thermal State of a Three-Layer Hollow Thermosensitive Cylinder Under the Conditions of Complex Heat Exchange

By using the straight-line method and conservative difference schemes, we reduce the nonlinear nonstationary boundary-value problem of heat conduction for a three-layer hollow cylinder to a Cauchy problem for a system of ordinary differential equations, which is solved numerically with the help of the formulas of backward differentiation. The conservative discretization of the heat conduction equation and the boundary conditions with respect to the space variable is performed by the integro-interpolation method. We also analyze the influence of temperature dependence of the thermal characteristics of the chosen materials on the temperature field formed in the layers of a three-layer cylinder.

Features of the welded seam material crystalliza-tion in Ti-TiB alloy under electron-beam welding conditions

Natural metal composite materials represent a promising class of modern structural materials that need to be welded. Such materials can be welded by fusion, as has been established with the Ti-TiB alloy as an example. The enhanced operational properties of such materials are determined by the microstructure, which is characterized by the presence of microfibers of borides, carbides, or silicides in the metal matrix. To preserve the mechanical properties of materials in a welded joint, it is necessary to ensure the formation of reinforcing microfibers in the welded seam material. Determination of formation mechanism of boride microfibers, originated in the welded seam material, will become the basis for optimizing of fusion welding modes, in particular, electron beam welding mode.
 The purpose of this study is the determination of formation mechanism of boride microfibers originated in the welded seam material. Two most probable variants of the formation mechanism are analyzed, which involve eutectic decomposition during crystallization from a liquid melt or eutectoid decomposition from a metastable crystallized alloy. The third version is a mixed variant of the two above-mentioned mechanisms.
 In the article the results of metallographic analysis of features of boride phase distribution and an analysis of elemental composition of boride fibers based on local Auger electron spectroscopy are presented. The object of study was a Ti-TiB alloy joint obtained by electron-beam welding. The analysis factors were the features of size, orientation, and nature of the distribution of boride phase microfibers in different areas of the welded seam. The characteristic elemental composition of boride microfibers, which characterizes the correspondence to equilibrium phases, is also studied.
 The degree of deviation of the ratio of boron and titanium in such a phase from the thermodynamically equilibrium in different layers of the material of the welded seam, formed by an electron beam in vacuum, is determined. The dependence of boride phase distribution under various conditions of heat exchange in the welded seam material on the side surfaces and in the central regions is established. It is shown that some of boride microfibers formed in the material of the welded seam are characterized by a deviation from the thermodynamically stable composition ТіВn (n = 1) to ТіВn (n = 0.85). The dendritic nature of boride microfibers distribution and the presence of meta-stable phase formations on Ti and B basis provide the grounds for proposing the predominant mechanism for the formation of structure of the welded seam material in the Ti-TiB alloy during crystallization.
 An analysis of hypothetical variants of the formation mechanism of boride microfibers originated in the welded seam material showed that the formation of a dendritic type of structure is characteristic for the growth of crystals of a new phase in the liquid phase. Such growth is characterized by the formation of equilibrium phases. The presence of a significant amount of non-equilibrium boride phase in the welded seam indicates the residue of non-equilibrium boron in the titanium matrix and continuation of growing of boride fibers in the crystallized welded seam. A determined mechanism for formation of boride microfibers originated in the welded seam material is eutectic decomposition during crystallization from a liquid melt with the formation of TiB microfibers and further growth of such crystals due to eutectoid decomposition from a metastable crystallized Ti-TiB alloy. The results obtained make it possible to understand the mechanism of formation of a welded seam in welded natural-composite metal materials, which permits to develop the recommendations for optimizing the welding technology for such materials.

Study of the Heat Exchange and Relaxation Conditions of Residual Stresses Due to Welding of Austenitic Stainless Steel

The present study presents a numerical prediction of residual stresses (RS) using the single-pass tungsten inert gas (TIG) welding process for stainless steel plates and the two-pass TIG welding process for stainless steel pipes. The effect of heat exchange between welding material and the environment was studied. The work consists of two parts: The first one is based on the determination of the existence of residual stresses numerically using Cast3M software, which has been validated by literature results. The second part addresses the means envisaged to attenuate the amplitudes of these residual stresses by practical methods. Two parameters with significant influence on the residual stresses have been chosen: the welding bead thickness and the torch displacement speed. The finite element model used has been validated experimentally, and the results obtained for the residual stresses have been compared with those given by the numerical study. The results obtained were found to be in agreement with references results. In addition, the microstructural analysis of different areas after welding of the solder joint (base metal, heat-affected zone and solder zone) was carried out using optical microscopy analysis.

The spark plug’s thermal state simulation

BACKGROUND: Spark plugs are among the most important components of the ignition system of an internal combustion engine (ICE). The spark-over produced by the ignition system should have sufficient energy for combustion initiation at any engine operation mode in all the service conditions. Start properties, reliability, power, fuel efficiency and exhaust toxicity of an ICE essentially depend on excellence of design and manufacturing quality of a spark plug. On the other hand, functional properties of spark plugs depend on concordance to ICE with main dimensions, design, heat properties and value of a spark gap. AIMS: Use of the methods of the spark plugs temperature field simulation in order to reduce the amount of experimental studies and to reduce the number of specimen options subjected to laboratory and on-road engine tests.
 METHODS: The simulation model of the temperature field of a spark plug of an internal combustion engine (ICE) was developed in this study.
 RESULTS: The representation of temperature distribution in the insulators thermal cone and other ceramic elements of a spark plug was obtained. The dependence of thermal conductivity and specific thermal capacity of corundum ceramics on temperature was derived. The dependencies of thermal conductivity coefficient of the plugs ceramic insulator are presented. The analysis of thermophysical properties of the substances made of various materials was carried out. The equations of the temperature field of all parts of a spark plug (a contact head, glass sealant, an insulator, a central electrode, a spark plugs body, a heat-sinking washer, a sealing ring, a cylinder head) were developed. The schematic representation of the spark plug geometry, used in the temperature field calculation, was obtained. The requirements for boundary conditions for calculation of the temperature field of a spark plug were determined. The calculation scheme of the spark plug is presented. The condition of heat exchange at the boundary between the selected part of a cylinder head and the cooling system of an internal combustion engine was considered. The study of heat transfer between the structural elements of a spark plug and the air inside the ICE compartment was carried out. The dependencies describing the heat exchange between the structural elements of a spark plug being in thermal contact with each other were determined and the internal boundary conditions were established.
 CONCLUSIONS: The presented methods and algorithms of spark plugs thermal state simulation helped to perform the calculation of dependencies of thermal conductivity and specific thermal capacity of the insulators ceramics as well as the thermal conductivity coefficient of the plugs ceramic elements on temperature.

Methodology for assessing the heat potential recovery regime at food industry enterprises

Areas of improving energy saving and the environmental situation in the processing and food industry In Ukraine are relevant, as technologies and equipment by their nature and degree for efficient use of fuel resources are practically achievable for their improvement, especially today. The purpose of the study is to improve the methodology for the optimisation of the mode of reuse of the thermal potential of exhaust process gases in the implementation of a two-stage cooling process. The indicators of process gas emissions with a volume consumption of 0.54 m3 /s and temperature – 1600°C with the parameters of the furnace operation A2-SHBG were used to construct local temperature characteristics. Their construction is carried out based on the heat balance and heat transfer at short surface intervals, considering the parameters of coolant flows. The results were analysed by the Flow Vision software suite under the structure of the graph, according to the laws of thermodynamics. A method for calculating the amount of cold heat agent for reuse in the technological process is proposed. It is established that under the accepted heat exchange conditions, the required amount of atmospheric air with an initial temperature of -300°Ccan be heated to a temperature of +640°C, and with an initial temperature of +300°C, can be heated to +1450°C. Natural gas consumption will change from 20 m3 / h, without preheating atmospheric air, up to 12.7 m3 /h when heating atmospheric air in the heat exchanger at an initial temperature of + 300°C. It is stipulated that when calculating energy resource savings, it is necessary to consider the initial temperature of the cold heat agent when using the heat of exhaust process gases. The proposed method for calculating the optimal heat recovery mode allows calculating changes in the consumption of the primary fuel and energy resource and creating a database for the effective implementation of energy-saving technologies when reusing waste gas heat into production

SIMULATION OF THE THERMAL MODE IN THE PIGLETS’ LOCATION AREA WHEN USING AN IR IRRADIATION PANEL

It has been shown that the efficiency of engineering systems for creating a microclimate at livestock facilities is determined by the possibility of organizing the required thermal conditions in interaction with external temperature parameters of enclosing structures. (Research purpose) The research purpose is developing a method for calculating and modeling the thermal mode in the piglets’ location zone using an infrared irradiation panel in a system of diffusely absorbing and radiating surfaces. (Materials and methods) Considered the conditions of a comfortable thermal regime for young animals, the physical model of a piglet, the conditions of heat exchange. The areas of temperature change of the irradiating panel and the influence of the configuration of the optical characteristics of the system shell when creating comfortable conditions for keeping piglets, depending on the age and temperature parameters of the enclosing structures, were presented. (Results and discussion) It was found that the computational model of heat transfer of an animal on the example of a piglet in a system of isothermal diffusely absorbing and radiating surfaces serves as an extension of existing computational methods. (Conclusions) It has been shown that the mathematical model of heat exchange of an animal in a system of diffusely absorbing and radiating surfaces more fully reflects the interrelationships in the elements of the biotechnical system, this allows more accurately forming and maintaining the specified temperature conditions for the comfortable maintenance of young animals. We have obtained a functional model reflecting the dependences of the thermal state of piglets, taking into account their age, on the ambient temperature, the design parameters of the radiating panel and its temperature on the surface. The main correlations linking the conditions of thermal comfort of piglets with the temperature of the radiating surface of the panel, with the temperature and optical properties of the enclosing structures of the room were revealed. The scheme of the algorithm for calculating the surface temperature of the radiant panel was given. The range of panel surface temperature values was determined depending on the temperature of the enclosing structures for the conditions of a comfortable thermal condition of animals in the heating zone, taking into account their age.

Intensification of heat-exchange of a direct-flow steam boiler of a coil type based on an educational laboratory stand

In the work under consideration, using an experimental stand formed by a cylindrical coil, the modes of air movement through the flue of a ramjet steam boiler were investigated. Experimental studies have revealed shortcomings in the operation of a direct-flow steam boiler and proposed ways to increase heat transfer in a steam boiler by turbulizing the gas-air flow in the convective part of the boiler flue. The Ansys programmable engineering environment was used to simulate the heat exchange between waste gases and water in the heat exchanger. The Ansys SpaceClaim program was used to design the geometric model. Finite element grid was created using the Ansys Icem CFD program. In the process of creation, materials were selected and designated for each part of the model, water and steam temperatures inside the heat exchanger, exhaust gas temperature, boundary conditions and heat exchange conditions between them were also set. After entering all the parameters the model calculations were carried out and the results were presented in the form of a temperature distribution diagram. In conclusion, a variant of further research of aerodynamic processes in a ramjet steam boiler and a demonstration of the selected option were presented.

Study of the influence of temperature dependent viscosity on fluid flow in annular channels

For all liquids, a change in viscosity depending on temperature is characteristic. In most cases, this dependency is commonly overlooked; however, when studying the flow of liquids under conditions of intense heat exchange, the temperature-dependent viscosity can have a significant impact on mass and heat transfer processes. It should be noted that for some liquids, such as polymer solutions or biological fluids, the temperature dependence of viscosity can be extremely complex and nonlinear. In such cases, ignoring this dependence can lead to inaccurate results and errors. Annular channels find wide applications in various technical systems, including heat exchangers and hydraulic devices. Understanding the factors influencing the fluid flow and discharge in such channels is a key aspect of optimizing their design and operation. One of the main factors influencing the flow process and fluid discharge in annular channels is the temperature-dependent viscosity of the fluid. This work investigates the influence of the thermo-viscous parameter with monotonic and non-monotonic temperature-dependent viscosity, as well as the geometric parameter of the annular channel on the fluid flow process and discharge. The mathematical model includes the continuity equation, Navier-Stokes equations, and the temperature equation. The method of control volume and the SIMPLE algorithm, modified to account for the variable viscosity coefficient, were applied for the numerical solution of these equations. It is shown that in the case of liquid flow in an annular channel with a monotonic dependence of viscosity on temperature, the steady-state discharge closely approaches the discharge at maximum viscosity. However, in the case of a liquid with non-monotonic viscosity dependence on temperature, the discharge significantly depends on the thermo-viscous parameter.

Evaporation of a water layer under local non-isothermal heating

• Water layer evaporation under local heating was investigated. • Gas convection effect was several times greater than diffusion and buoyancy of vapor. • Local heating allowed achieving high values of the heat transfer coefficient. • Obtained results were important for the development of new methods of heat exchange enhancement. The evaporative behavior of a water layer and the heat transfer under local heating were investigated. Non-stationary and non-isothermal heat exchange conditions were created by laser heating. The thermal field on the free surface of the layer was registered using thermal imaging technology. Changes in the liquid mass due to evaporation were determined using the gravimetric method. The key factors affecting water evaporation were estimated and the characteristic heat fluxes associated with evaporation, radiation and convection are compared. The effect of free convection in the gas phase on the evaporation rate of the water film is several times higher than the effect of diffusion and buoyancy of vapor. The local heating allowed achieving high values of the heat transfer coefficient and heat fluxes at considerably smaller liquid temperatures and heating area, which is advantageous from an energy point of view. The obtained results were important for the development of new methods of heat exchange enhancement, as well as for the prediction of heat fluxes and hydrodynamic flows and evaluation of non-isothermal, non-stationary and inhomogeneous heat exchange.

MODES OF ADHESIVE BONDING LAYER FORMATION DURING ROLL MOTION IN THE PROCESS OF SHEET LAMINATION

Novel technologies for the synthesis and processing of materials and products based on these materials, such as additive manufacturing, require the use of mathematical modeling to study the accompanying physical and chemical phenomena. These technologies include sheet lamination, which today has a variety of applications and numerous modifications. This article presents a model of adhesion layer formation in the creation of multilayer composites, which is controlled by a hot roller moving along the surface of the top layer. The dynamics of reagent heating depends on the thermal properties and sizes of all layers, the temperature of the roller, and its pressure against the surface, with characteristic times and spatial scales for different processes. The transition to dimensionless variables allowed the identification of dimensionless complexes to determine different modes of development of the adhesion layer synthesis process. Based on the combustion theory and non-equilibrium thermodynamics, new criteria of the process initiation and transition to a quasi-stationary mode were elaborated. The behavior of various thermodynamic quantities was analyzed in detail, including heat storage in the heated layer, enthalpy excess, and entropy production. The reaction zone is wide in most cases. The dependences of the half-conversion time on the model parameters are plotted for a finite layer size. This is a new characteristic for sheet lamination technology. A controlled mode, a fast bulk synthesis mode, a slow transformation mode maintained by the heat stored in the inert materials, and a quasi-stationary mode are identified. Criteria were established for different modes of reactions under conjugate heat exchange conditions.

Cr2O3 Doping Effect on Silica Glass Cooling Rate

In this paper we present the results on the effect of the SiO2 melt cooling rate on the morphology of its surface. The method of atomic force microscopy explores a surface roughness of the silica glass cooled at different rates after its heating up to more than 2100 °C. The study compares three modes of cooling glass rods with a diameter of 14 mm: convective heat exchange with the surrounding air, quenching with dropping the sample into a vessel with water, and radiation of silica glass doped with 0.1 wt% Cr2O3. The surface roughness of silica glass in the second and third modes of cooling was significantly less than in the conditions of convective heat exchange. Doping the silica glass with Cr2O3 increases the heat exchange coefficient by 2 times and decreases the surface roughness. The results of the research can contribute to improving the mechanical and optical properties of silica glass light guides.

Influence of the conditions of internal heat exchange on the process of thermal decomposition of carbonates in iron ore raw materials

This work considers influence of heating rate of iron ore raw materials on chemical and metallurgical processes of thermal dissociation of carbonates, which occur during its high-temperature roasting. The research was conducted for the temperature ranges of the existing roasting and sintering machines, taking into account macro-kinetics of calcination processes. Substantial influence of heating rate of iron ore samples on kinetics of thermal decomposition of carbonates was revealed. The cause of the effect of internal heat exchange conditions in reacting iron ore sample on macro-kinetics of dissociation reaction for carbonates was substantiated scientifically. Influence of nonisothermal properties on precision of thermal analytical investigations, which were conducted using the methods of non-isothermal kinetics with different heating rates of iron ore samples, was studied. The authors suggested the mathematical model, which allows to take into account wide range of variations of the parameters in kinetic equations and volumetric thermal and chemical-metallurgical dissociation processes for carbonates. A series of calculating experiments, aimed on reveal of the relationship between heating rate of iron ore samples and evolution of concentration fields, transformation rates and temperature gradients, was carried out using the suggested model. The obtained results can be used for development of the optimal operating conditions for sintering and roasting machines, which propose optimization of heat treatment processes for iron ore preparation, owing to intensification of heat and mass exchange processes during high-temperature roasting. These conditions are considered as optimal from the point of view of power- and resource efficiency. Forming of the above-mentioned conditions allows to decrease fuel and power expenses for thermal preparation of raw materials at metallurgical production facilities, as well as to lower total economical production charges due to use of thermal decomposition of carbonates. The reported study was funded by RSF according to the research project № 22-11-00335.

BTA Deep Hole Vibration Drilling for Nickel-Based Alloys: Cooling Patterns and Cutter Tooth Wear Mechanisms.

The high cutting temperature and poor thermal diffusion efficiency of nickel-based alloys during deep hole machining have become technical challenges in the hole machining field. In this paper, a finite element simulation model of Inconel-718 BTA ordinary drilling and vibration drilling processes was established by using Deform-3D finite element simulation software. The variations in the temperatures of the tool teeth and the workpiece at different positions of the nickel-based alloy under ordinary drilling and vibration drilling were investigated. Additionally, the wear pattern of each tool tooth under the two drilling methods was further analyzed by building an experimental platform for workpiece temperature detection, which reveals the wear and cooling mechanism of nickel-based alloy BTA deep hole drilling. The results show that the average temperatures of the external, intermediate, and central teeth were reduced by 18.1%, 21.1%, and 17.8%, respectively, during vibration drilling. In addition, the workpiece hole wall and hole bottom temperatures were reduced by 5.7% and 4.6%, respectively. To conclude, the experimental tests were consistent with the simulated temperature trends. BTA vibration drilling optimizes the heat exchange conditions between the cutter teeth and the workpiece during the drilling of nickel-based alloys, which effectively reduces the cutting temperature and, thus, improves the wear resistance of the cutter teeth.

About Calculation and Forecast of Temperature in the Layer Cell of Self-Heating of Raw Materials in a Silo

The article clarifies an approximate variant for calculating the temperature in an inhomogeneous layer cell without a clear boundary under the assumption of significant distance in its center between the upper and lower ends of the silo when heat exchange conditions have little effect on the development of temperature in the layer cell due to poor thermal conductivity. The normal Gaussian law concerning distribution of thermal sources in the cell on an axis of a silo is accepted. The integral cosine of the Fourier transform is used to construct the analytical solution of the nonstationary thermal conductivity problem. A compact formula for calculating the increase in excess temperature in the center of the self-heating cell over time is derived and used to identify the parameters of the cell. The change in temperature at other points of the raw material is expressed through incomplete gamma function that is reduced to the probability integral. Calculations show that for the selected distribution of thermal sources, the temperature increase slows down rapidly with separation from the center of the cell. The possibility of determining the pattern distribution of the localized field of excess ambient temperature over time is proved. Examples of density identification of thermal sources are given. After identification, the calculation formulas become consistent with the experiment and suitable for the theoretical prediction of temperature rise in the raw material. The approbation of the proposed mathematical expressions to identify the parameters of the self-heating process of raw materials showed high accuracy relative to experimental data with a deviation of 0.01–0.015%. It is possible not only to determine the parameters of the self-heating cell but also to predict the time of reaching a flammable temperature in it.