Home – Home – Jornals – Journal of Mining Sciences 2015 number 5

This article addresses the heat transfer in a peristaltic flow of a reactive combustible viscous fluid through a porous saturated medium. The flow here is induced because of travelling waves along the channel walls. It is assumed that exothermic chemical reactions take place within the channel under the Arrhenius kinetics and the convective heat exchange with the ambient medium at the surfaces of the channel walls follows Newton's law of cooling. The analysis is carried out in the presence of viscous dissipation and without consumption of the material. The governing equations are formulated by employing the long-wavelength approximation. Closed-form solutions for the stream function, axial velocity, and axial pressure gradient are obtained. It is found that the temperature decreases at high Biot numbers, and the Nusselt number increases with increasing reaction parameter. The Biot number and reaction parameter produce the opposite effects on the Nusselt number.

In this paper, non-similarity solutions for natural convection heat and mass transfer along a vertical plate with a uniform wall temperature and concentration in a doubly stratified porous medium saturated by a fluid are obtained. The Darcy--Forchheimer-based model is employed to describe the flow in the porous medium. The nonlinear governing equations and their associated boundary conditions are initially cast into dimensionless forms by using pseudo-similarity variables. The resulting system of nonlinear partial differential equations is then solved numerically by using the Keller-box method. The effects of the buoyancy parameter, Forchheimer number, and thermal and solutal stratification parameters on the dimensionless velocity, temperature, concentration, and heat and mass transfer coefficients are studied.

An unsteady three-dimensional stagnation-point flow of a nanofluid past a circular cylinder with sinusoidal radius variation is investigated numerically. By introducing new similarity transformations for the velocity, temperature, and nanoparticle volume fraction, the basic equations governing the flow and heat and mass transfer are reduced to highly nonlinear ordinary differential equations. The resulting nonlinear system is solved numerically by the fourth-order Runge−Kutta method with the shooting technique. The thermophoresis and Brownian motion effects occur in the transport equations. The velocity, temperature, and nanoparticle concentration profiles are analyzed with respect to the involved parameters of interest, namely, unsteadiness parameter, Brownian motion parameter, thermophoresis parameter, Prandtl number, and Lewis number. Numerical values of the friction coefficient, diffusion mass flux, and heat flux are computed. It is found that the friction coefficient and heat transfer rate increase with increasing unsteadiness parameter (the highest heat transfer rate at the surface occurs if the thermophoresis and Brownian motion effects are absent) and decrease with increasing both thermophoresis and Brownian motion parameters. The present results are found to be in good agreement with previously published results.

A mathematical model of the effect of a medium on a homogeneous rigid body whose outer surface includes a circumferential cone is considered. The complete system of equations of motion under quasistationarity conditions is given. In the dynamic part forming an independent third-order system, an independent second-order subsystem is distinguished. A new two-parameter family of phase portraits on the phase cylinder of quasivelocities is obtained.

The shock-wave loading of a gradient mixture is numerically investigated in the pressure range of 20−150 GPa. The shock compression of a platelet gradient mixture of tungsten and porous copper is considered using a model which is a modification of the model of platelet porous materials supplemented with an algorithm for calculating changes in the thermodynamic and kinematic parameters of each particle and the sample as a whole. It is shown that the calculated parameters of the state of this shock-compressed mixture in the pressure−particle velocity coordinates are consistent with experimental data for a real tungsten−copper mixture.

This paper presents a solution of a sequence of coupled problems of thermoelastoplasticity which study the occurrence and development of flow in a material layer under pure shear conditions, and its subsequent deceleration by slowly removing the load. The homogeneity of the stress state of the layer is excluded due to the coupling of thermal and deformation processes in the presence of a temperature dependence of the yield point. An additional source of heat is taken to be its production by friction of the material layer on a rough plane. The conditions for the occurrence of viscoplastic flow in the deformable material layer and the laws of motion of the boundaries between the elastic and plastic regions in this layer are determined, and the flow velocities and large irreversible and reversible deformations are calculated. It is shown that reversible deformations cause stresses in the flow region and the moving elastically deformed core.

A mathematical model of the electro−gas−dynamics of a gas−particle system is described. A numerical method for solving the system of equations is proposed, and an analysis is made of the motion of charged solid aerosol particles in gas−particle flow in the electric field produced by the corona electrode of the atomizer, the grounded surface on which deposition is performed, and the charge of the aerosol particles in the interelectrode space. The solution is based on the two−velocity two−temperature model of a monodisperse medium without phase transitions and coagulation assuming that only the carrier medium, described by the Navier−Stokes equations for a compressible gas, has viscosity. The dispersed phase is defined by the equation of conservation of mass, the equations of conservation of momentum components taking into account the Coulomb force and aerodynamic friction, and the equation of conservation of internal energy. The system is written in generalized coordinates in dimensionless form and solved using the explicit McCormack method with splitting over the spatial coordinates and a conservative correction scheme. The velocity and density fields of the gas−particle mixture were investigated in the interelectrode space and near the surface on which solid aerosol particles in the gas−particle flow are deposited.

This paper presents a theoretically study of the boiling of superfluid helium on a cylindrical heater placed in a coaxial porous shell in microgravity. Steady-state transfer processes at the interface are studied using molecular-kinetic methods. The Boltzmann transport equation is solved by the moment method based on the four-moment approximation in the form of a two-sided Maxwellian. The obtained solution is used to calculate the heat flux density in film boiling on a cylindrical heating surface in the case where the film thickness is comparable to the diameter of the heater. The motion of the normal component of the superfluid liquid in pores is described by equations that take into account heat and mass transfer in superfluid helium. The relation between the vapor film thickness and the structural characteristics and geometrical dimensions of the porous shell is obtained. Analysis of the results of the calculations is given.

In this paper, the effects of viscous dissipation, nonuniform heat source/sink, magnetic field, and thermal radiation on the heat transfer characteristics of a thin liquid film flow over an unsteady stretching sheet are analyzed by the homotopy analysis method. The effects of various physical parameters on the heat transfer characteristics are found. The study shows that the thermal radiation parameter has a significant effect on the surface temperature. It is also found that nonuniform heat sinks are better suited for cooling purposes. Furthermore, the limiting cases are obtained and are found to be in good agreement with numerical results previously published by other authors.

The dynamic antiplane strain of an incompressible cylindrical body is studied in a nonlinear formulation in actual variables. A representation of the velocity and acceleration through the displacement is obtained. The problem of the body deformation with account for geometrical and physical nonlinearities is reduced to an initial boundary-value problem for the displacement. The displacement found is used to determine the pressure and stresses. For a body with a quadratic elastic potential, plane waves and self-similar motion are studied. The linear potential is used to investigate the deformation of a hollow elliptical cylinder for which analytical expressions for displacement and stresses are found and the external load is determined. It is shown that, due to the degeneration of the inner cavity of the body to a plane section, the load on the section remains limited.

An analytical algorithm for studying the stability of the equilibrium of compressible hyperelastic sphere with Lagrange variables is proposed. The problem is solved in a spherical coordinate system in a general three-dimensional formulation using linearized stability theory and the method of separation of variables with respect to the radial displacement, the displacement due to the rotation, and the resulting strain in the principal directions. Results of numerical and graphical analysis of the stress--strain state for a three-layer-sphere are used to analyze the gravity stress--strain state of the lithosphere of the Kuril island arc system.

A model of a medium consisting of parallel layers of elastic rectangular blocks separated by deformable viscoelastic interlayers is considered. The model is proposed for describing the low-frequency part of the spectrum in waves propagating in media with such a structure. For a two-dimensional assembly consisting of 36 blocks, the results of numerical calculations are compared with experimental data.

Based on the model of a physical cut and a material layer on its continuation, elastic and elastoplastic problems of determining the stress−strain state inside and outside the layer in the case of loading of cut edges by an antisymmetric system of forces are posed and solved. The solution of the elastic problem is compared with the solution obtained within the framework of the Neuber−Novozhilov model. In contrast to the latter model, the proposed approach provides results consistent with experimental data on the process of formation of fracture regions. Based on the analysis of the discrete solution of the problem, regions of plastic deformation and regions of possible fracture are found.

A new approach is proposed to estimate the fracture of bodies with V-shaped notches under loading of two types. Two examples of quasibrittle fracture are considered: with an initial straight crack and with a sharp V-notch. Experimental data are obtained on the fracture of V-notched specimens under bending.

A boundary singular integral equation of the plane problem was constructed using an approach based on the representation of the unknown Lekhnitskii complex potentials in the form of Cauchy type integrals with unknown densities on the boundary of the region occupied by the body. The contours of the holes and cuts and the shape of the outer boundary are exactly or approximately represented in the form of a sequence of straight and curved (in the form of elliptical arcs) boundary elements. The unknown densities on the boundary elements are approximated by a linear combination of some regular functions or complex functions that have a known singularity. In the numerical solution of the integral equation by the collocation method or by the least-squares method and in the subsequent calculations of the stress--strain state, the integrals of all types along the boundary elements are calculated analytically, which significantly increases the accuracy of the results.

The quality of cutting of low-carbon and stainless steel by beams of fiber and CO₂ lasers with oxygen or nitrogen being used as a process gas is compared. The cut surface roughness for sheets from 3 to 10 mm thick is determined. Domains of optimal (in terms of the minimum roughness criterion) application of lasers of various types in the space of dimensionless parameters (Peclet number and dimensionless power) are found. It is demonstrated that the CO₂ laser is more effective for laser-oxygen cutting, while the fiber laser is more beneficial for cutting with the use of a neutral gas.

In this paper, we consider the classical Burke-Schumann problem as applied to the construction of a mathematical model of a diffusion flame spreading over a fuel film deposited on a thin substrate. This formulation is used to model the combustion of a gaseous fuel flowing from a thin slot (half-width x_in and mixed with oxidizer flowing from a parallel slot (with the outer boundary x_out). The key parameters determining the position of the flame front in the space are identified: the Peclet number Pe, the stoichiometric parameter A dependent on the equivalence ratio, and the geometric parameter X_in = x_in/x_out. The dependences of the flame length on these parameters, including x_out → 8, are analyzed. Comparison shows good agreement between calculated and experimental

Conductive heat losses from the base of a lean methane--air inverted flame stabilized behind the trailing edge of a thin rod have been experimentally evaluated. The results favor the view that the heat losses to the flame holder play a crucial role in the inverted flame stabilization and blow-off. Simple estimations have been performed, which indicate that the well-established correlation between the mixture composition and the boundary velocity gradient at the flame holder, usually considered as a proof of the flame stretch theory of blow-off, can be explained without involving the flame stretch concept. The suggested explanation of this correlation is based on the assumption that the heat loss to the flame holder is the main factor that determines the inverted flame blow-off behavior and on the similarity between the mechanisms of energy and momentum diffusion in gases (Pr ≈ 1).

A possibility of using some kinetic models for the description of detonation of a gaseous hydrogen-air mixture is justified. A hierarchy of mathematical models from the simplest model of combustion under static conditions to the model of unsteady nonequilibrium gas dynamics is numerically constructed. Verification is performed on the basis of experimental data on the ignition delay time as a function of temperature and on the detonation wave velocity as a function of dilution of the mixture by argon or nitrogen. A mathematical technology for the description of cellular detonation propagation in channels of various engineering devices is developed on the basis of detailed and reduced kinetic mechanisms of nonequilibrium chemical transformations within the framework of the ANSYS Fluent commercial software system. It is demonstrated that the cell size in a mixture diluted by argon by 92% in a channel 30 mm wide is in good agreement with experimental data.

This paper presents a model for the steady-state filtration combustion of carbon mixtures with a solid incombustible material in opposed gas flow containing an endothermic oxidizer such as steam and/or carbon dioxide. A computation scheme for calculating the characteristics of the process (combustion temperature and composition of the products) is proposed for the case where the product composition is determined by the thermodynamic equilibrium in the high-temperature zone. For stoichiometric regimes, finite analytical expressions are obtained that relate the combustion temperature and the composition of the products with the oxidizer gas composition and the proportion of carbon in the carbon/solid inert material mixture. Predictions of the model are in qualitative agreement with published experimental data.

The problem of calculating the characteristics of the agglomerates formed during combustion of high-energy composite solid propellants is considered. It is shown that the mathematical models developed by the authors can be used for different propellant formulations to evaluate not only the dispersion of agglomerates, but also their quantity, chemical composition, and structure. The rules (algorithm) of using the developed models for a wide range of propellant formulations are determined. Modeling results for a number of propellant formulations based on various components are analyzed.

A physicomathematical model within the framework of the approach of mechanics of reacting heterogeneous media is proposed to describe the combustion wave in a mixture of a gas and fine magnesium particles. The model is verified on the basis of dependences of the limiting temperature of ignition and combustion wave velocity on the radius and volume concentration of particles. It is guaranteed that the model is valid in the range of particle radii from 7.5 to 35 μm and in the range of volume concentrations of particles (1.2–2.4)·10^–4.

An explanation for multiple repetitions of a nonisothermal wave process in one sample is proposed. The explanation is based on synthesis and decomposition of a metastable product. A mathematical model of this phenomenon is constructed and studied. The resultant characteristics of synthesis and decomposition waves are compared with available experimental data.

Thermokinetic data on the oxidation of ASD-4 powder modified by impregnation with V₂O₅ gel were obtained by thermogravimetry and differential scanning calorimetry under heating in air to 1250 °C at a rate of 10 deg/min. The phase formation process directly during oxidation of the modified ASD-4 was studied by powder x-ray diffraction method using a synchrotron radiation source. A mechanism for the effect of V₂O₅ on the oxidation of ASD-4 is proposed on the basis of literature data and analysis of the results of the studies performed.

The effect of preliminary mechanical activation of low-calorific-value powdered formulations in a planetary ball mill on the main parameters of the subsequent thermal explosion has been studied. It has been found that in mechanically activated compositions, the initiation temperature of thermal explosion is reduced by hundreds of degrees. The maximum decrease (1300 °C) is observed for the Ti + 4 wt.% C system. Regimes of preliminary mechanical activation of reaction mixtures and the subsequent thermal explosion conditions producing Ti₃Al and Ni₃Al single-phase intermetallic compounds with nanometer grain size were determined. For the 3Ni + Al composition, the energy accumulated during mechanical activation was evaluated. It is shown that the initiation temperature of thermal explosion in the MA compositions studied can be used to estimate the temperature that develops in the mill drums.

A method of correction of particle image velocimetry (PIV) data for reconstruction of the gas velocity based on the particle velocity in supersonic underexpanded jets is considered. The method is based on estimating the velocity lag of tracer particles on the basis of their velocity relaxation parameter as a correction to PIV data in the Newton approximation of interphase interaction. It is shown that the velocity relaxation parameter of tracer particles in flows with velocity jumps can be determined from the initial PIV data. Correction with the found parameter of velocity relaxation of the phases provides good accuracy.

A method of shock wave overpressure reconstruction is presented, which allows overcoming the drawbacks of the previous approaches associated with the lack of shock wave velocity measurement points and the limitations of the empirical formula. An optimal design of the testing system is proposed. Based on the optimal system, the shock wave velocity field is inverted with the use of the generalized inversion theory, and the overpressure distribution is obtained. The inversion results are preferable to empirical results because the experimental data are confirmed in a limited area. Methods of overpressure computation and visualization are described.

The effect of high-temperature shock compression conditions on the degree of transformation of silicon nitride into a cubic gamma-modification at pressures of 36 and 50 GPa in planar recovery ampoules is studied. The x-ray Rietveld method is used to determine the quantitative phase composition before and after shock compression. The temperature reached during compression and the residual temperature after unloading are calculated. It is shown that the use of high-temperature shock compression at 36 GPa provides a higher transformation level compared to the classical approach based on the addition of copper powder into the samples.

This work presents the results of experiments on the compression of a spherical copper shell loaded by the detonation of a plastic explosive layer. A U-70 accelerator is used for radiographic recording of the convergence of the shell to the center, and metallographic analysis of the copper shell preserved after the experiment is performed. The results of multiframe proton radiography of the convergence of the inner boundary of the copper shell to the center are compared with the results of numerical simulations.

It is proposed to carry out burning of the launch vehicle nose fairing after it has completed its mission on the descent trajectory from the moment of separation to an altitude of 5-10 km. Burning is carried out in the Earth atmosphere with additional heating of the faring material due to the reaction of pyrotechnic mixtures. Various pyrotechnic mixtures for use in the nose fairing are discussed.

The article presents argumentation in favor of transition to high bench stripping in open pit mines in Kuzbass, which will increase coal production and improve mine performance. The authors find functional connection between the duration of the transition to high bench stripping and the increase in the finite depth of an open pit mine. Substantiation is given to choosing the height of a bench based on the change in relationship of operating costs and a cut layer height. The practical significant of the research is development of a new approach to validating expediency of high benches for mining with truck&shovel and creation of a procedure to find increment in ultimate pit contour in transition to stripping with high benches.

Advanced technologies and modern high-production machines for underground mining of thick gently dipping coal demand strict adherence to technological discipline, reduction in operational loss and selection of optimized ventilation modes. The authors analyze ventilation schemes used in working areas in thick gently dipping seams in order to reveal influence exerted by the schemes, methods and parameters of ventilation on distribution of air loss in mined-out areas.

The article reports research findings in the area of open pit coal mining and substantiates alternative technologies based on new technological and organizational principles of open pit mining. Using the method of geometrical analysis of an open pit mine field and technological design of mining systems, stage-wise mining technologies have been developed for the case when mining front advance is changed. Such technologies ensure the improvement of a wide range of technical-and-economical and ecological performance of an open pit mine. The main flow charts of the mining sequences are interconnected with natural-technological groups of deposits, that influence cross-wise configuration of an open pit (ultimate contour) and structural characteristics (parameters) of working areas and generate geometrical type of an open pit field.

Under discussion is the equipment for open pit mining of limited coal reserves. Methods of overburden dumping are systematized. A new dumping method is offered; it allows reducing land withdrawal by means of utilizing adjacent open pit. The author presents relations for area of internal dumping, considering coefficient of dumping in the adjacent open pit and the volume of the adjacent open pit. The feasibility of overburden placement in mined-out pits is analyzed.

In focus is fuel briquetting using coal mining and processing waste. The authors present an integrated technology of coal and coke dust processing, including oil agglomeration of input components and fuel briquetting using binder. The optimal binder is chosen to be heavy coal-tar. Influence of a type of compaction and content of different binders on strength of fuel briquettes is analyzed. The quality characteristics of concentrate obtained from dressed coal and coke dust and fuel briquettes made of the concentrate are presented.

The authors review methods to assess reliability of forecasting of peak vibration velocities under large-scale production blasting using statistical analysis of regression residuals. The regression analysis of experimental data and the subsequent statistical analysis of the regression residuals is exemplified.

The article describes integrated experimental research into mechanisms of change in physical properties of soil under electrochemical reinforcement implemented in a test area. The monitoring methods involved geological engineering survey, laboratory testing of soil samples, as well as statistical, geomechanical, seismic, electrical and georadar sounding. It has experimentally been proved that three zones (strengthening, dehumidification and transient) are formed in the interelectrode space; the ranges of space and time change in humidity, deformation modulus, cohesion, internal friction angle, elastic wave velocities, electrical resistivity and integral parameters of georadargrams are found. The authors substantiate ways of improving efficiency of two- and one-stage schemes of electrochemical soil reinforcement and application areas of geophysical monitoring techniques.

The authors construct 3D probabilistic cellular automata to model accumulation of elementary damages and evolution of their cluster structure. Kinetic dependences of number of the clusters and evolution of time correlation functions are studied for the number of clusters and number of elementary damages. It is proved that intersection of the time autocorrelation function of a random process “number of impulses of emission” with the local minimum in the field of negative correlation can be interpreted as a sign of transition of a loaded material to a stage immediately preceding irreversible failure.

The presented information is a part of the authors’ research in the field of effect exerted by innovative development of coal business on competitiveness of a region. The described conceptual model of innovation-based transformation of the coal industry in Kuzbass rests upon coordination of interests of business and authority with the purpose to improve competitive ability of a region. With this model, it is proposed to develop a route map for modernization of regional coal mining industry, which should create conditions for the coal industry to change over from being a donor to becoming a driver of economics in the Kemerovo region. At the same time, this will enable appraisal of federal and regional reserves to be efficiently used in implementation of this ambitious, difficult and expensive “project”.

The article describes the analysis of theoretical and applied aspects of ecological risk management in terms of coal mining and processing companies, as well as assigns and solves tasks on identification of ecological risks, assessment of probability of undesired events, determination of structure of probable damage, assessment of risk, estimation of technological and organizational methods and measures of influence on ecological risk to reduce and avoid it, and decision-making on practical introduction of particular risk management and control measures. The groups of technological and organizational measures aimed to minimize or neutralize risks are considered. The key result of the research is the package of measures of ecological risk reduction, in particular: technologies of ultradeep purification of dielectric liquids; introduction of processing equipment for used-up tyres of heavy open pit dump trucks; formation and updating of quality management system; improvement of efficiency of reclamation of disturbed lands; treatment of hydraulic mining and coal processing waste.