- Browse by Author

### Browsing by Author "Zhevzhyk, Oleksandr V."

Now showing 1 - 11 of 11

###### Results Per Page

###### Sort Options

Item Analysis and Ways for Advancing of Mathematical Model of Pulverized Coal Ignition and Combustion(Інститут геотехнічної механіки ім. М.С. Полякова НАН України, 2022) Zhevzhyk, Oleksandr V.; Potapchuk, Iryna Yu.; Pertsevyi, Vitalii O.; Sekar, ManigandanShow more ENG: An analysis of mathematical models of ignition and burning of a single particle and a coal cloud is given. Models which take into account the presence of ash in particles, the influence of the ratio of the amount of coal and primary air (excess coefficient) and the size of coal particles on the ignition process are presented and analyzed. It is shown that simplifications in mathematical models in most cases lead to a loss of accuracy and therefore the results cannot be used for practical purposes. Simulation of complex air supply processes by approximation of uniformity also leads to questionable results. A significant influence on the ignition and combustion of coal particles affects the content and intensity of the release of volatile substances and the chemical reactions that occur in this case. The rate of volatiles yield is proposed to be calculated according to the Arrhenius law, and the activation energy and frequency factor are considered to be those that do not depend on the type of coal, but are determined only by the temperature of the particle. Taking into account heat transfer by radiation and a decrease in the particle diameter during combustion has a positive effect on the results obtained. According to the results, the reactivity and losses with underburning significantly depend on the initial diameter of coal particles. Most models do not take into account the change in temperature inside the particles during heating, ignition and combustion in the apparatus, but there are works that are specifically devoted to the study of temperature fields inside the particles and the influence of the particle shape on the combustion rate. Modeling showed that motion relative to the gas leads to an intensification of heat transfer between the particles and the environment, while the volatile matter yield time decreases at a high ambient gas temperature. A decrease in the rate of combustion chemical reactions is noted with an increase in the concentration of water vapor in the gaseous medium around the particle, i.e. oxygen diffusion is the limiting factor in particle combustion. The most complete and physically correct gas dynamics during combustion is calculated in models where known turbulence models are used, such as the standard k-ε model, RNG k-ε model, BSL model and SST model. At the end of the article, the concepts for improving the model of ignition and combustion of coal particles are outlined.Show more Item Experimental Study of the Thermal Reaming of the Borehole by Axial Plasmatron(НТУ «Дніпровська політехніка», 2019) Voloshyn, Oleksii I.; Potapchuk, Iryna Yu.; Zhevzhyk, Oleksandr V.; Yemelianenko, Volodymyr; Zhovtonoha, Mykola M.; Sekar, Manigandan; Dhunnoo, NishthaShow more EN: Purpose. To study rock spallation dynamics in the process of the borehole thermal reaming and analyze energy consumption of the borehole thermal reaming process by plasma jets of the axial plasmatron. Methods. Field experimental study of rock spallation by plasma jets is carried out with the view to measuring the thermal power of plasma, weight of rock spalls and duration of plasma jets impact on the borehole. VT-200 scales were used to measure the rock spalls weight. In the experimental study, plasma jets flow out directly into the borehole in the granite block. The borehole and plasmatron nozzle parameters are geometrically similar. Findings. Experimental data are processed in the form of a table that shows the following parameters of individual experiments: duration of the borehole surface treatment by a plasma jet; thermal power of a plasma jet; heat release of a plasma jet, weight of the rock spalls, energy efficiency of the rock spallation process; productivity of the rock destruction. Experimental data are processed in the form of the dependence of energy consumption of the borehole thermal reaming on the duration of the borehole inner surface thermal treatment. The range of thermophysical and plasmodynamic parameters of the plasma torch that allow to achieve rock spallation is determined. Originality. The linear relationship between the energy consumption in the process of the borehole thermal reaming by low temperature plasma and the duration of the reaming process is revealed, with energy consumption of the reaming process decreasing dramatically with the increase in the process duration. Practical implications. Methodology of the experimental research into the borehole thermal reaming by plasma jets rock spallation is developed. The results of the study could be applied to borehole drilling processes.Show more Item Experimental Study of the Thermochemical Treatment of the Low-Grade Coal Prior to Boiler Combustion at Coal-Fired Power Station(EDP Sciences, 2019) Yemelianenko, Volodymyr I.; Pertsevyi, Vitalii A.; Zhevzhyk, Oleksandr V.; Potapchuk, Iryna Yu.; Lutai, OleksandrShow more EN: Abstract. Analysis of the perspectives of the coal fuel for thermal power plants is carried out. The necessity of the experimental study for temperature measurement in the boiler furnace. The results of the experimental study are presented: temperature change over time at the burner outlet for different constant pressure value of the backlighting gas, dependence of the temperature at the burner outlet from the backlighting gas pressure for constant concentration value of pulverized coal in coal-air mixture, dependence of the temperature at the burner outlet from the concentration of pulverized coal in coal-air mixture for constant value of the backlighting gas pressure, temperature measurements for constant backlighting gas pressure value, constant value of the concentration of pulverized coal in coal-air mixture when plasmatron is switched and operates for some time range. The results of the study could be applied to the solid fuel treatment for different thermal units.Show more Item Influence of the Heat-Transfer Stream Pressure on the Surface of the Rock in a Process of the Thermal Reaming of the Borehole(Національний гірничий університет, Дніпро, 2018) Voloshyn, Oleksii I.; Potapchuk, Iryna Yu.; Zhevzhyk, Oleksandr V.Show more EN: Purpose. Experimental research on the high-speed interaction of the heat transfer medium jet with the surface of the borehole in the process of fragile rock destruction with the purpose of determination of the heat transfer medium velocity along the borehole surface and the heat transfer coefficient from the heat transfer medium to the rock surface. Methodology. Methods of comparative analysis, mathematic and physical simulation modelling as well as experimental research are used. Findings. The methodology of experimental research on high-speed interaction of the heat transfer medium jet with the surface of borehole as the lateral surface of the cross duct imitated the rock surface in a borehole is developed. Experimental research that consisted of pressure measurement on the lateral surface of the cross duct at the air jet impingement on the lateral surface is conducted. Experimental research treatment is executed as dependence of absolute pressure at the lateral surface of the cross duct, i.e. absolute pressure on the rock surface, from relative pressure of air before a nozzle and relative diameter of the cross duct. Dependences between the values of pressure before a nozzle and values of pressure on the rock surface, values of relative diameter of the cross duct, nozzle outlet diameter, inner diameter of the cross duct and values of air pressure along the lateral surface of the duct are determined. Originality. The work presents physical imitational modelling of high-speed interaction of the heat transfer medium jet with the surface of the borehole in a certain range of geometrical parameters of the cross duct and the nozzle, that is accepted in accordance with geometrical similarity to the technological and processing parameters of plasmatron and borehole diameter before the beginning of thermal reaming process. Practical value. Expediency of high-speed plasma jets application as a thermal tool in the processes of fragile rock destruction and, in particular, in the processes of thermal reaming of the boreholes is substantiated.Show more Item Influence of the Leakage in Air Supply Networks on the Efficiency of Application of Pneumatic Backfill Equipment(Dnipro University of Technology, Dnipro, 2023) Ponomarenko, Serhii; Potapchuk, Іryna; Zhevzhyk, Oleksandr V.; Kabakova, Liudmyla; Potapchuk, AnnaShow more ENG: Purpose. Determining the influence of the degree of pneumatic energy losses in the non-hermetic air supply network on the efficiency of using installed equipment in the pneumatic method of waste utilization from mining and beneficiation of minerals. To achieve this purpose, a tightness control device was developed using the method of fixed volumes. Methods. Using the molecular-kinetic theory of gases, the thermodynamics and hydrodynamics laws, the characteristics of an open thermodynamic system under excess pressure and with a degree of a capillary-type leakage are investigated. Pneumatic energy losses in the pneumatic supply pipeline are determined by the mass of compressed air leaked due to its poor tightness. Findings. The peculiarities of the tightness control of hollow products by the method of fixed volumes have been summarized. The dependences of non-production losses of compressed air and the corresponding pressure drop on the geometric characteristics of the air supply pipeline, the leakage in supply pipeline, and the time of assessing the degree of leakage have been determined. Originality. For the first time, the relationship between the parameters of compressed air in an open thermodynamic system under excess pressure during air leakage and its heat exchange with the environment has been revealed. The influence of compressed air leakage in air supply networks on the efficiency of using vibration-pneumatic machines with an annular ejector in backfill technologies has been determined. Practical implications. The research results can be used to improve the existing or develop the new technological schemes of air supply equipment that use pneumatic energy at mining and metallurgical enterprises. Minimization of energy consumption can significantly expand the scope of application of pneumatic backfilling method.Show more Item Mathematical Modeling of Rocks Plasma Disintegration Process at Borehole Reaming(IOP Publishing Ltd, 2023) Potapchuk, Iryna; Zhevzhyk, Oleksandr V.; Kholiavchenko, Leonid; Pertsevyi, Vitalii; Bosyi, Dmytro O.; Drubetskaya, Tanya; Potapchuk, AnnaShow more ENG: The mathematical model of thermal disintegration of rocks during the reaming of boreholes, which takes into account the compatibility of the thermogas dynamic problem for a high-temperature heat transfer agent and the thermal problem for the rock heated by this heat transfer agent, has been developed. The mathematical model is based on the laws of conservation of mass, quantity of motion and energy and takes into account the dependences for determining the thermal stresses and the temperature of brittle fracture of rocks. As a result of solving the equations of the mathematical model, the temperature distribution in the rock mass (magnetite quartzite) during heating in the process of borehole plasma reaming and productivity of the borehole plasma reaming process are obtained. Calculated and experimentally determined productivity of the process of plasma reaming of the borehole were compared.Show more Item Mathematical Modeling of the Borehole Heating Process by Means of Axial Plasmatron(Інститут геотехнічної механіки ім. М.С. Полякова НАН України, 2022) Zhevzhyk, Oleksandr V.; Potapchuk, Iryna Yu.; Yemelianenko, Volodymyr I.; Sekar, Manigandan; Pertsevyi, Vitalii O.Show more ENG: The article presents a mathematical model that allows determining the main parameters of the plasmadynamic coolant jet in the process of thermal heating of the borehole inner surface. The mathematical model of lowtemperature plasma motion along the wellbore consists of the k-ε turbulence model equations, the continuity and energy equations for the gas flow, and the non-stationary heat conduction equation for calculating the temperature of a cylindrical flange pipe, which models the rock mass around the borehole. The equations are written in a cylindrical coordinate system for the radial and longitudinal components of the velocity of a low-temperature plasma flow. The differential equations of the mathematical model were supplemented with the corresponding initial and boundary conditions. The initial conditions were the known gas temperatures in the borehole and the initial temperature of the cylindrical flange pipe. The boundary conditions, in addition to the corresponding relations for the turbulence model, were the known parameters of the plasma flow at the inlet to the cylindrical pipe and the conditions for stabilization of the flow at the outlet. Noslip conditions for the flow and boundary conditions of the third order for the energy equation and the heat equation were used on the fixed boundary of the flanged pipe. To calculate the equations of the mathematical model, the numerical finite element method was used. The adequacy of the model of the borehole heating process by the plasma flow was verified by comparing the numerical calculation with experimental data. Experimental data confirm the adequacy of the proposed mathematical model. The difference between numerical and experimental data does not exceed 4.1 %. The proposed mathematical model can be used to calculate the temperature of the inner surface of the borehole before it is chipped during heating.Show more Item Mathematical Modeling of the Gas Dynamic Parameters of Impinging Heat-Transfer Medium Jet in Borehole Thermal Reaming Process(National Academy of Sciences of Ukraine (NAS of Ukraine), 2019) Bulat, A. F.; Voloshyn, Oleksii I.; Potapchuk, Iryna Yu.; Yemelianenko, Volodymyr I.; Zhovtonoha, Mykola M.; Zhevzhyk, Oleksandr V.; Manigandan, S.Show more EN: Introduction. As compared with other ways of thermal destruction of rocks, the rock destruction by low temperature plasma jet has advantage in terms of distribution of cracks in rock at a considerable depth, high heat transfer coefficient and high specific heat flux, simplified system of automation and remote control, and compactness of thermal tool. Problem Statement. Thus, the possibilities of analytical determination of optimal parameters of thermal effect on rocks are limited by solution of thermoelasticity equations and contact problems of strength theory. Such formulation of the problem is unacceptable due to complication of taking into account substantial changes in the physical and thermos-physical rock properties while heating and applying mechanical load. Due to abovementioned facts it is obviously necessary to develop a mathematical model that enables to define basic gas dynamic jet parameters of heat-transfer medium in the process of borehole thermal reaming. Purpose. The purpose of this research is to develop a mathematical model for calculating the gas dynamic characteristics (pressure, density, and velocity) of the heat-transfer medium while it is moving along the surface of the borehole in the thermal reaming process. Materials and Methods. Mathematical modeling of the flow process for free and impact jets of heat-transfer medium using a PC. Results. Experimental studies have confirmed adequacy of the developed mathematical model for calculation of gas dynamic characteristics (pressure, density, and velocity) of the heat-transfer while it is moving along the surface of the borehole in the process of its thermal reaming. Conclusions. The obtained results can be used for modeling the gas dynamic characteristics in the case of applying a thermal tool with electric discharge in other technologies of heat treatment and destruction of materials.Show more Item Results of the Experimental Research of the Heat-Transfer Jet Pressure to the Rock Surface During Thermal Reaming of the Borehole(НТУ « Дніпровська політехніка», 2018) Voloshyn, Oleksii I.; Potapchuk, Iryna Yu.; Zhevzhyk, Oleksandr V.; Zhovtonoha, Mykola M.Show more EN: Abstract. The performed analysis of scientific sources confirms the existence of a small number of publications devoted to the experimental research of the gasdynamics and plasmodynamics of jets used as a heattransfer medium in the thermal methods of mine rocks destruction. There are almost no experimental and theoretical publications related to the multiple-jet plasmotrons research. The expediency of own experimental researches performing has been substantiated concerning the lateral inflow of heat-transfer medium high-speed jets on the borehole surface. An experimental research has been made of the interaction between the heattransfer medium high-speed jets and the surface of the borehole imitated by the through duct. The further prospects of this work are the following: to determine the gas velocity along the lateral surface of the through duct and the value of the heating capacity coefficient from the heat-transfer medium to the lateral surface of the through duct, which imitates the rock surface in the borehole. These parameters are required for creating a mathematical model of the brittle destruction of rocks.Show more Item Study of the Plasma Flow Interaction with the Borehole Surface in the Process of its Thermal Reaming(НТУ «Дніпровська політехніка», 2018) Voloshyn, Oleksii I.; Potapchuk, Iryna Yu.; Zhevzhyk, Oleksandr V.; Horiachkin, Vadym M.; Zhovtonoha, Mykola M.; Yemelianenko, V.; Semenenko, Yevhen; Tatarko, L.Show more ENG: Purpose. Study of the plasma flow interaction with the borehole surface in the process of its thermal reaming for determination of transient temperature distribution along the borehole surface and the average coefficient of heat transfer from the plasma flow to the borehole surface. Methods. Experimental study of the plasma flow interaction with the flange union with internal lateral surface simulating the rock surface in a borehole has been carried out. The essence of the experimental study is in measuring temperature of the flange union external side while the plasma flowing inside the flange union. To measure temperature on the external surface of the flange union, a chromel-alumel thermocouple with thermoelectrodes of 1.2 mm in diameter was used. In experimental research, plasma flows out through a nozzle directly to the flange union made of copper. The parameters of the flange union and the nozzle of plasmatron are geometrically similar. Findings. Experimental data are processed as a relationship between the temperature of the copper flange union lateral surface, i.e. borehole surface, and the time of the copper flange union heating by the heat carrier. Experimental data are processed as a dependence of temperature of the tin pipe side surface, i.e. surface of the borehole, on the location of temperature measurement point along the tin pipe and the time of the tin pipe heating by the heat carrier. Originality. Physical simulation modeling of the heat carrier (low temperature plasma) flow interaction with the borehole surface simulated by the copper flange union and the tin pipe in a certain range of geometrical parameters of the copper flange union, tin pipe and the plasmatron nozzle as well as thermophysical properties of the heat carrier assumed in accordance with geometrical similarity to the technological and design parameters of the plasmatron and borehole diameter before the beginning of thermal reaming process. Practical implications. Methodology of experimental research of the heat carrier (low temperature plasma) flow interaction with the borehole surface that was simulated by the copper flange union of the tin pipe is developed. The results of the influence by high-temperature heat carrier jets on the processes of fragile rock destruction are rather useful in the borehole drilling processes.Show more Item Thermodynamic Analysis of the Gas Parameters Distribution under Leakage from a Closed Volume with Rigid Walls(EDP Sciences, 2019) Ponomarenko, S.; Zhevzhyk, Oleksandr V.; Vuginshteyn, Alex; Lutai, O.Show more EN: Abstract. The work deals with the thermodynamic analysis of the parameters of the gas in a closed volume with rigid walls, during its leakage and heat exchange with the environment. Based on the first law of thermodynamics, the law of Fick and the equation of the gas state, we obtained an equation that characterizes the effect of temperature gradient on the mass gas leakage in parallel processes of leakage and heat transfer. The regularity of the leakage coefficient change, determined by the diffusion coefficient, depending on the mass-average temperature in a closed thermodynamic system, is established. The variation of the leakage coefficient for the corresponding ranges of temperature gradients are shown. The research results can be implemented in the development of techniques and technologies for monitoring the tightness of hollow products under excessive pressure of the gas medium.Show more