Gas-dynamic Processes Research Articles

Gas-dynamic processes and causes of accidents at mines

Geodynamic phenomena that occur during the exploitation of a coal-bearing massif lead to human casualties, reduce the speed of penetration, and significantly complicate the operation of the mine.The article analyzes existing views on geodynamic processes occurring within mining fields located in coal-bearing formations. A safe technology for identifying potential outburst locations during coal mining is characterized. The technology has been tested during prospecting and environmental studies within the mining workings at active mines and abandoned mining fields. The results of profile and planar investigations in he areas exhibiting geodynamic outbursts in coal deposits and mines are presented.When sampling subsoil air using the technology of structural-thermo-atmospheric-hydrogeochemical research (STAHGS), which is carried out on the surface of the earth in profile and planar versions, the authors came to the conclusion about the possibility of predicting fault zones of increased permeability and zones of low fluid permeability. The first affect the rate of destruction of rocks under pressure, and in the second case, the possibility of gas emissions into the mine, which can be accompanied by an explosion and fire. Such zones are dangerous, because the most destructive events occur in places of collision. Early identification of places of geodynamic stress of rocks, fault zones of increased permeability, accumulation of gases – all this will allow to make a decision in advance about changing the conditions of conducting mining operations and degassing of the coal massif.In addition, the authors draw attention to hydrogen gas as one of the causes of initiation of explosions and fires during underground mining operations in mines, which is not taken into account at the current stage of safety control of mining operations. The possible cause of a hydrogen explosion is not taken into account in coal mine accidents. The appearance of hydrogen and helium in coal samples taken from the mine may indicate the deformation of the massif, which leads to the opening of cracks and the outflow of gas from deeper horizons. And then an increase in the concentration of hydrogen, not methane, creates the conditions for explosions and fires.

STUDY OF THE PROGRAMMABLE ISOKINETIC SAMPLER EFFICIENCY FOR OF ECOLOGICAL DIAGNOSTICS SYSTEMS OF HEAT ENGINES AND BOILER PLANTS

The work is devoted to the solution of the actual scientific and practical task of creating a universal sampling device for systems of environmental diagnostics of heat engines and boiler plants of various purposes. Ensuring the isokinetic mode of sampling from the exhaust pipe (EP) of the engine is a more difficult task than carrying out a similar sampling process in the chimney of the boiler plant, since the exhaust gases of the engines are characterized by fluctuations of static pressures in the HT with an amplitude of up to ±500 Pa, which must be taken into account in the operation of the sampling equipment. In the course of research, based on the analysis of global and domestic experience in the production and use of equipment for environmental certification of internal combustion engines and boiler houses, a programmable isokinetic sampler (ICT) was created, which allows you to take a proportional part of the gas sample from the full flow of exhaust gases in the EP of the power plant with accuracy ±3%. Motorless and motorized test stands have been developed for modeling and research of gas-dynamic processes in the exhaust systems of engines and boiler plants, which provide the possibility of varying the parameters of gas flows - mass flow rate, speed, temperature, static pressure, velocity pressure in the ranges: 15 - 55 g/s; 5...30 m/s, 20...180 °С, 0...2.5 kPa, 10 - 550 Pa, respectively. On the basis of the created test stands, empirical dependences were established to determine the static pressure differences between the ICP and EP pipelines, in which the isokinetic mode of sampling is ensured, from the dynamic pressure of the gas flow in the EP. With the help of these dependencies, SMART control of the programmable ICP is carried out. An experimental development of the programmable ICP was carried out as part of the MT-1 minitunnel during environmental tests of the 1СН12/14 diesel engine in separate modes and according to the ESC cycle established by the UNECE Regulations R-49. The research results confirmed the compliance of the created sampling device with regulatory requirements for its design and the accuracy of determining the sampling coefficient.

Limits of self-ignition in the process of hydrogen-methane mixtures release under high pressure into unconfined space

The promising way for the storage of gaseous combustible mixtures based on hydrogen is the use of high-pressure vessels. However, as a result of accidental release of such mixtures under high pressure into atmosphere the self-ignition could arise. In the paper a series of numerical simulations of hydrogen/methane mixtures release from the high-pressure vessel into the open space is carried out in order to investigate safe conditions for storage and pumping of such mixtures. The storage pressure is varied in the range from 350 to 700 atm, that correspond to the pressure range promising for hydrogen storage. Main attention in the paper is paid to the variation of methane content in its mixture with hydrogen. It is shown that under any pressures considered there is a limit of methane content in its mixture with hydrogen providing the absence of self-ignition of combustible hydrogen-methane mixture. Herewith, the certain value of critical methane content depends on geometry of hydrogen/methane source (hole, slit, its size). In particular, results of the study demonstrate that in the case of small orifice self-ignition limits are wider when the combustible mixture is released through the slit than through the round hole. At the same time, when the large orifice is used this difference levels off. It is shown that the intensity of gas-dynamic processes decreases with the increase in the methane content, and thereby there is a certain decrease in the temperature of shock-heated air and self-ignition probability.

Vacuum Plasmatrons with Hollow Cathode: Gas-Dynamic Plasma Processes in the Hollow Cathode

Vacuum Plasmatrons with Hollow Cathode: Gas-Dynamic Plasma Processes in the Hollow Cathode

ИССЛЕДОВАНИЯ ГАЗОДИНАМИЧЕСКИХ И ГИДРОДИНАМИЧЕСКИХ ПРОЦЕССОВ В ПОЛОСТЯХ И КАНАЛАХ ВАКУУМНЫХ ЗАХВАТНЫХ УСТРОЙСТВ

The article discusses the results of studies of gas-dynamic and hydrodynamic processes in cavities and channels of vacuum gripping devices operating in air, water and mixed media. Transient processes were obtained that occur in the cavities of the gripping devices from the moment the vacuum generator is powered up to the moment of the steady-state vacuum level.

Визуализация тепловых потоков в высокоскоростном течении за ударной волной

The paper presents the thermographic studies of unsteady heat fluxes behind a plane shock wave in the rectangular 24x48 mm shock tube test section. Consecutive panoramic visualization of the heat fluxes plots on streamlined walls after the plane shock wave interaction with a rectangular obstacle fixed on the channel wall are obtained. The duration of the recorded thermal processes is up to 40 milliseconds after the shock wave passage. The heating and cooling of the test chamber walls streamlined by supersonic flow are visualized using the Telops FAST M200 high-speed infrared camera (operating range 1.5 – 5.1 microns) through the quartz windows transparent to infrared radiation. Visualization of the thermal fields were compared with the shadow images and results of 2D numerical simulation of a nonstationary gas dynamic process after the diffraction of a shock wave with Mach numbers M=2.0-4.5.

Numerical Study of Gas-Dynamic and Thermal Processes in a Pulsed Electric Discharge

Numerical Study of Gas-Dynamic and Thermal Processes in a Pulsed Electric Discharge

Searching for Possible Design Solutions to Extend the Service Life of the HPC of a Powerful NPP Turbine after Damage to the Rotor Blades

The aim of this research was to analyze and evaluate possible design solutions for the flow path of the high-pressure cylinder (HPC) of the K-1000-60/3000 turbine and the possibility of their short-term implementation in a nuclear power plant after an accidental destruction of the working blades of the last stage of the HPC in conditions of the shortage of generating capacities and a tense operation state of the power system. To achieve the set goals, an appropriate methodology was developed; a mathematical model of thermo-and gas dynamic processes in the flow path of a steam turbine was improved. To make appropriate decisions on changing the design of the turbine, the necessary computational studies of the HPC of the K-1000-60/3000 turbine of the designed structure, the structure without rotor blades of the 5th stage and the structure with four first stages (without the fifth stage) were carried out for both turbine steam flows. The results of the study of thermo- and gas dynamic parameters of the flow showed the presence of differences in the operating conditions of all turbine stages, and these are the most significant for the 4th and 5th stages. A significant redistribution of thermal differences in the stages, and a decrease in the internal power of the HPC of the turbine by 35.5 MW and 6.6 MW respectively, as well as a decrease in their internal efficiency by 11.8 % and 2.1 %, respectively, were noted. Taking into account all the aspects related to the operation of the power unit, the most successful solution for the rapid resumption of operation of a powerful turbine plant used by a nuclear power plant after an accidental damage to the working blades is a HPC design without the working blades of the fifth stage. It is planned to carry out additional studies of the HPC design by replacing the nozzle apparatus of the fifth stage with an appropriate simulator.

Development of an Algorithm for Calculation of the Effective Parameters of a Blast Pulse during Explosive-Reactive Destruction of a Rock Mass

The change in the spectral density of a stress pulse during the operation of an explosive facility in the rock mass is simulated. An algorithm has been developed for calculating the distribution of the spectral density of the pressure pulse for nonstationary gas-dynamic processes, taking into account the physical and mechanical properties of rocks.

Gas-Dynamic Processes in a Rotating Cylinder in the Presence of Axial Temperature Gradients

Gas-Dynamic Processes in a Rotating Cylinder in the Presence of Axial Temperature Gradients

APPROXIMATION OF THE THERMOPHYSICAL PROPERTIES OF HIGH-TEMPERATURE GAS

For the numerical study of high-temperature gas-dynamic processes, approximating dependences of the thermophysical properties of air on temperature are proposed. The approximation error averaged over the temperature series does not exceed 0.87%. Air at high temperatures in terms of molecular transport properties is quite close to other loose multicomponent partially dissociated and ionized gas mixtures, such as products of rocket fuel combustion in a rocket engine nozzle. The advantage of the approach to the development of approximating dependences of the physical properties of high-temperature gases is the possibility of their use in multifunctional software packages for numerical simulation and engineering analysis. The approximating dependences of thermo physical properties were used to study by means of the ANSYS software package the processes occurring in the nozzles of rocket engines. The physical characteristics of the air, calculated according to the proposed dependences, ensured that the polytropic index corresponded to the data on the combustion products of a real rocket engine. A mechanism is proposed for matching data from different sources due to the deterioration of the approximation in the vicinity of the boundary. The use of the technique for well-consistent data is acceptable and does not lead to a noticeable decrease in the approximation quality near the boundary. An approach is proposed for approximating multiparameter dependencies.

Study of the Gas-Dynamic Features of the Design of the Gas-Air Path of the Plasmatron

The aim of the study is to consider a method for improving the energy efficiency of the technological process of plasma recovering of turbine blades of CHP through the development and implementation of a three-way vortex mixer into the design of the plasma torch. By changing the operating parameters of the mixer, it is possible to adaptively control not only the recovery modes, but also the physical and mechanical properties of the coating. It has been established that structural changes in the technological elements of the plasmatron significantly change its structural characteristics, which leads to a change in the gas-dynamic processes occurring in it. The changes consist in the appearance of additional hydraulic and gas resistance to the flow of the carrier gas with the powder composition. Modernization of the plasmatron and optimization of technological regimes require a gas-dynamic calculation of each element of the gas-air path at the design stage. Studies of the principles of pressure distribution, flow rate, changes in the flow rate of the transporting gas and powder composition made it possible to design the optimal design of the plasmatron while retaining its technical characteristics, regulated by the GOST 4.140-85 standard «System of product quality indicators. Electric welding equipment. Nomenclature of indicators»

Modeling and Complex Analysis of the Topology Parameters of Ventilation Networks When Ensuring Fire Safety While Developing Coal and Gas Deposits

Underground mining, including underground coal mining, is accompanied by accidents and fire hazards that pose a threat to the life safety of miners. The fire hazard increases with an increase in the mining depth. Currently, most accidents in coal mines are mine fires. The cost of eliminating mine fires is 80–95% of the cost of eliminating all accidents occurring at mining enterprises. Therefore, the problem of developing a new methodology for modeling the ventilation network parameters of the mine to increase the reliability of controlling the aerogas mode at the excavation site is very relevant. The comprehensive analysis and assessment of gas-dynamic processes in coalmines under study were carried out using the methods of probability theory and mathematical statistics. Spatial data were processed using spline interpolation in “gnuplot”. As a result, a generalized expression for the transfer functions of coalmine objects, taking into account delays, was developed, including the description of dynamic properties of mining sites under various operating modes. The principal possibility of using a graphical method for estimating additional parameters of the sections of the ventilation system branches has been proved due to the alignment of their profiles at an equivalent distance relative to an arbitrary analogue. The improved method of spatial modeling was used to determine the gas-dynamic characteristics through additive gas-dynamic processes. The studies have been carried out and the method for managing the process of changing connections between devices (controllers–switches) of the technical system was developed in order to obtain greater reliability for safe mining. In subsequent studies, there is an issue of more detailed clarification of the peculiarities concerning the interrelations between the studied parameters in several projections of the response space.

A novel approach for manufacturing cellular metallic structures using pulsed gas dynamic spraying process

A novel approach for manufacturing cellular metallic structures using pulsed gas dynamic spraying process

NON-EQUILIBRIUM SUPERSONIC FLOW AROUND A BLUNT

The computational model designed for studying the processes of non-equilibrium physicochemical gas dynamics in supersonic rarefied-air flow past a blunt plate of finite dimensions under the laboratory experiment conditions is formulated. The computational model is based on the two-dimensional Navier–Stokes equations, the energy conservation laws for the translational degrees of freedom of atoms and molecules and the vibrational degrees of freedom of diatomic molecules, and the chemical kinetics and diffusion equations for individual components of partially ionized gas flow. The basic gas dynamic and kinetic processes in flow past a blunt plate are analyzed at the Mach numbers M = 10 and 20. It is shown that regions of thermal nonequilibrium are formed.

Simulation of the Nonstationary Gasdynamic Processes and Conjugate Heat Transfer in the Working Cavities of Pulse-Periodic Systems

Simulation of the Nonstationary Gasdynamic Processes and Conjugate Heat Transfer in the Working Cavities of Pulse-Periodic Systems

Non-Equilibrium Supersonic Flow Past a Blunt Plate at High Angle of Attack

The computational model designed for studying the processes of non-equilibrium physicochemical gas dynamics in supersonic rarefied-air flow past a blunt plate of finite dimensions under the laboratory experiment conditions is formulated. The computational model is based on the two-dimensional Navier–Stokes equations, the energy conservation laws for the translational degrees of freedom of atoms and molecules and the vibrational degrees of freedom of diatomic molecules, and the chemical kinetics and diffusion equations for individual components of partially ionized gas flow. The basic gas dynamic and kinetic processes in flow past a blunt plate are analyzed at the Mach numbers M = 10 and 20. It is shown that regions of thermal nonequilibrium are formed.

Gas Dynamics of Micro- and Nanofluidic Systems

The size of micro- and nanofluidic devices accounts for their operation in modes that differ significantly from those for the corresponding macroscopic counterparts. Deep understanding of gas-dynamic processes occurring in micro- and nanofluidic systems opens new opportunities for the practical use of molecular transport at the micro- and nanoscale. Models and simulation methods with high reliability are described. The article also outlines the important flow parameters which must be considered in the first place to correctly simulate gas-dynamic processes in micro- and nanofluidic systems. The review will be useful as a reference for researchers interested in implementing preliminary analysis in the development and optimization of micro- and nanofluid devices.

ДОСЛІДЖЕННЯ ВПЛИВУ ВОЛОГОСТІ ВУГІЛЬНОГО ПЛАСТА НА РОЗВ’ЯЗУВАННЯ ГАЗОДИНАМІЧНИХ ПРОЦЕСІВ У ВИБОЇ ГІРНИЧОЇ ВИРОБКИ

Purpose. Determination of influence of changes in the coal properties and phase permeability dur-ing moistening on the outburst hazard of the coal seam and calculation of the safe level of coal moisture. Methods. A mathematical model of the course of gas-dynamic processes in the mine face in the out-burst-hazardous zone near the tectonic fault has been developed, taking into account the presence of wa-ter in the crack-pore space of the coal. The system of equations has been solved using the finite element method. Calculations were performed for four cases: without taking into account the influence of water, with the influence of water on the change in phase permeability, with the influence of water on the modu-lus of elasticity and Poisson's ratio. Results. The calculation of geo-mechanical and filtration parameters under the condition of mini-mum natural moisture saturation sw=1% showed that under the desired boundary and initial conditions, a gas-dynamic process begins: the zone of inelastic deformations rapidly grows from the mine face along the coal seam, the methane pressure in the coal seam near the roadway rapidly drops, coal ejection oc-curs and a cavity is formed in the coal seam. Then geo-mechanical processes and the process of methane filtration return to a quasi-stationary state. As a result of performing a series of numerical calculations with varying moisture values in the crack-pore space of the coal seam, it was established that for the de-sired boundary and initial conditions, gas-dynamic process in the mine face begins when sw<24%. If this limit is exceeded, the gas-dynamic process in the near-face zone of the coal seam does not start. A de-crease in the phase permeability for methane leads to the neutralization of the outburst-hazardous prop-erties of coal. If we take into account the decrease in the value of the modulus of elasticity and the in-crease in Poisson's ratio when the water content increases in the crack-pore space of coal, then the safe limit of moisture saturation decreases additionally. Scientific novelty. The influence of changes in coal properties and phase permeability during hu-midification on the outburst hazard of a coal seam has been determined. The safe level of coal moisture saturation for desired boundary and initial conditions has been calculated. Practical significance. A numerical model has been developed that allows determining the safe lim-it of moisture saturation under specific conditions, at which the course of geo-mechanical and filtration processes in the coal seam does not acquire a dynamic character.

Formation of the near-face stress field under the influence of natural and technological factors

The mine face is a high-risk zone, where a loss of stability, an occurrence of dynamic and gas-dynamic processes, and an increase in the content of harmful gases are possible. All these negative consequences to certain extent depend on the near-face stress field. This article presents the results of numerical study of the peculiarities of its time-dependent formation in rocks with different properties, when using such means of reducing the outburst hazard as water injection and unloading cavities. It is shown that with the course of time in the rocks around the mine working, the area of increased difference of the stress tensor components spreads, which leads to the formation of cracks of varying degrees of intensity. The maximum component of the stress tensor increases; the abutment pressure zone is formed in the near-face region. The simultaneous increase of vertical stress in the abutment pressure zone and unloading of horizontal stress leads to displacement of the coal seam in the mine working and loss of the mine face stability. If the mine working is driven through hard rocks, Q* parameter values, as well as the maximum vertical stresses in the abutment pressure zone, are significantly increased. The zone of inelastic deformations begins to form with a long delay and has noticeably smaller dimensions. Hard rocks can withstand greater difference of the stress tensor components and greater vertical loads without breaking. Coal moistening leads to a significant decrease in the difference of the stress tensor components in the near-face zone of the coal seam. Values of Q* parameter in moistened coal in the three-meter near-face zone is 1.5–5 times lower than in the coal seam with a natural moisture content. The growth of the abutment pressure zone in moistened coal slows down; the zone of inelastic deformations becomes somewhat larger. The near-face stresses in the mine working with the unloading cavity is radically different from the previous cases. The peak values of Q* parameter and maximum stress are moved to the depth of unloading cavity. At the same time, both the difference of the stress tensor components and the maximum stress remain at a low level, which corresponds to moistened coal and in a long time interval ensures deformation of the near-face zone in the elastic mode. Unloading of this zone from rock pressure occurs in two directions: in the direction of the mine face and in the direction of the unloading cavity.