Gasdynamic Regime Research Articles

Development of Cf/C-UHTC composite and study of its resistance to oxidation and ablation in high-speed high-enthalpy air plasma flow

This article contains the results of research on the development of a Cf/C-UHTC carbon fabric composite based on a viscose precursor and a combined matrix consisting of partially sintered ceramics in a system consisting of HfC–HfB2–NbC–NbB2–TiC–TiB2–B4C–SiC, amorphous carbon, and pyrocarbon. The SiC fraction does not exceed 8.5–9.0 wt%. In its initial state, the composite has open porosity, with apparent and true densities of 18–22%, 2.25–2.29 g/cm3 and 2.79–2.91 g/cm3, respectively. The bending strength and the elasticity modulus are 27.8 ± 0.7 MPa and 7.8 ± 0.2 GPa, respectively, and the fracture strain is 0.85 ± 0.05%. The tests for resistance to oxidation and ablation were carried out in a gas dynamic flow regime and non-equilibrium air plasma heating at flow rates of 4.5–4.8 km/s and breaking enthalpy of 45–50 MJ/kg. Heating was performed in the temperature range Tw = 1400–2700 °C at the critical point on the front surface of the samples. The average linear ablation rate and mass loss rate of the composite are 6.3 ± 0.3 μm/s and 6.22 ± 0.44 mg/s. The estimated value of the conductivity factor is 0.280–0.285 W/(m K). The performance ability of the composite arises from the formation and evolution of a passivating heterogeneous oxide film consisting mainly of titanium niobate Ti2Nb10O29, mixed solutions of Hf1−xTixO2, (Ti1−xHfx)1−yNbyOz and (Ti1−xHfx)NbO4 with broad homogeneity ranges, and also encapsulated carbide and boride particles. It is shown that the oxidation resistance of the composite increases as a result of the transition through a number of phases into a liquid state as the working temperature increases.

Changing the working conditions of the mineral wool cupola during the transition from an open type to a closed one

The widespread use in the industry of mine furnaces of the wagon type requires the organization of management of their gasdynamic and thermal regime. In the mode of operation of a cupola with an open grate, its thermal mode is characterized mainly by the peripheral movement of gases with a significant difference in the ratio of heat capacities of gas flows and materials. The use of forced removal of exhaust gases from the shaft furnace contributes to an earlier transition from a peripheral to a predominantly central movement mechanism. By increasing the degree of rarefaction on the grate to 0,71‒0,73 bar, it is possible to increase the level of melt temperature, temperature pressure and air blast flow, exhaust gas temperature while improving the conditions of heat exchange between gases and heated materials. This process will be accompanied by a continuous decrease in the productivity of the unit with an improvement in the stability of the melting process. A further increase in the level of rarefaction on the grate contributes to the gradual transition of the mechanism of movement of gases from the peripheral to the central one with a deterioration in the parameters of the wagon melting.

Engineering-geomorphological assessment of gas-dynamic regimes of the Western Dvina river valley (within the Republic of Belarus) and surrounding areas

Engineering-geomorphological assessment of gas-dynamic regimes of the Western Dvina river valley (within the Republic of Belarus) and surrounding areas

Gas dynamic regimes observed in dual-pulse laser ignition

A numerical study of the gas dynamics induced by a dual-pulse laser pre-ionization plasma used in laser ignition applications is presented herein. Past experimental observations have revealed important differences in the gas dynamics of the dual-pulse plasma, generated by overlapping a pair of ultraviolet (UV) and near-infrared (NIR) pulses, as compared to those of single-pulse (typically near-infrared) laser breakdown that has been more commonly studied. The simulation results reported here show that the dual-pulse pre-ionization scheme can lead to various gas dynamic regimes depending on the axial offset of the focal points of the two beams along the optical axis. If the UV and NIR pulses are perfectly overlapped (no offset) the energy deposition is uniform along the optical axis, leading to the formation of a toroidal structure in the post-discharge cooling phase. Alternatively, if the NIR energy addition pulse is focused with a small axial offset, (i.e., upstream or downstream of the UV pre-ionization pulse by ~0.5 mm) then an asymmetric torus forms that exhibits a third lobe which propagates away from the main kernel (to the side where the NIR was focused). Finally, if the two beams are focused with a larger offset of ~2.5 mm (weaker coupling), then another regime with a fourth lobe can arise. The four main flow regimes revealed from the model are in agreement with OH* experimental chemiluminescence images. These flow regimes influence the development of the early flame kernels, therefore playing an important role in practical laser ignition applications.

The effect of steam on air gasification of mechanically activated coal in a flow reactor

A combined steam-gas plant with in-cycle steam gasification of coal and hot gas purification is considered as a promising technology for increasing the efficiency of energy production with simultaneous reduction in environmental impact. To intensify steam-air gasification, mechanical activation of fuel is used; it consists in high-stress grinding in a mill-disintegrator. The supply of steam to the gasifier allows an increase in reactivity of fuel, suppression of sorbent decomposition in the unit of hot desulfurization, reduction in the steam load on the shift reactor, increase in useful external work of gas turbine expansion, reduction in nitrogen oxide formation, and general increase in the efficiency and ecological compatibility of energy generation. On the other hand, a significant amount of steam can deteriorate the heat balance and efficiency of the gasifier. In this work, the influence of the steam/fuel ratio on steam-air gasification of mechanically activated Kuznetsk coal in a flow reactor was studied experimentally. The excess air coefficient was maintained constant and equal to 0.51, which corresponded to a temperature at the reactor outlet of about 1100?C. When steam was supplied, the fuel and air-flow rates were adjusted to ensure a constant gas-dynamic regime. To evaluate the obtained regimes, the heat and material balances were compiled. A positive effect of steam on characteristics of the gasification process was revealed. For the studied coal, the maximum degree of coal conversion and the calorific value of synthesis gas are achieved with a steam/fuel ratio of about 0.4 kg/kg.

Gas-dynamic structure of a plasma jet in He and Ar, striking the surface of a liquid and a plane dielectric

The results of experiments on the interaction of an argon plasma jet with a liquid are presented. The effect of a coaxial barrier discharge on the gas-dynamic regime of a plasma jet of helium, freely blown into ambient air, and also colliding with a solid surface, is studied. Three orientation helium jets were studied - the jet is directed up, down and horizontally. Schlieren images of a jet were compared with visible images of a plasma jet. It is concluded that the main effect of the discharge on the gasdynamic regime of the jet is associated with gas heating in the discharge zone.

Shock interactions in two-dimensional steady flows of Bethe–Zel’dovich–Thompson fluids

The morphology of nodes generated by the interaction of discontinuities in steady two-dimensional inviscid flows is examined. The fluids considered are Bethe–Zel’dovich–Thompson (BZT) fluids, which feature negative values of the fundamental derivative of gas dynamics in the vapour phase. The operating conditions correspond to the non-classical gas-dynamic regime where expansion shocks, compression fans and composite waves are admissible in addition to the classical compression shocks and expansion fans. Interactions caused by the crossing, overtaking and splitting of compression/expansion shocks, along with the refraction of these through a contact discontinuity, are analysed here. The well-established method of wave curves is applied to non-classical wave curves, revealing a variety of interaction patterns that are simply not admissible in classical gas dynamics. It is shown that shock waves can be reflected, transmitted and refracted as Prandtl–Meyer fans or composite waves. Based on numerical evidence, the splitting (and consequently the Mach reflection) of an expansion shock seems to be disallowed. Theoretical considerations on the admissibility of such configurations are also provided. The present analysis is relevant to applications potentially involving supersonic flows of BZT fluids, e.g. organic Rankine cycle power systems, and can also be used in front-tracking algorithms for general equations of state.

A new level of blast furnace control in the developments of the IFM

Under today’s conditions, characterized by the instability of the composition and quality of charge materials, the composition of the combined blast, as well as the significant variability in the intensity of heat, the timely expert evaluation of the current heat parameters and reasons of their variations comparing with the setup parameters is rather actual. The expert evaluation can allow to issue recommendations to reach the setup technical and economic indices while minimizing the energy costs. The main features of the decision-making support intellectual system for blast furnace heat control, developed by the Institute of Ferrous Metallurgy, presented. The system based on the heat conditions diagnostic with application of evaluation criteria of heat conditions and BF heat gas-dynamic regime, effectiveness of axes coke funnel, evaluation of the form, location and thickness of the plastic zone in a blast furnace and other criteria, based on technological parameters of BF heat and control systems information. It was noted, that the elaborated system allows to evaluate adequately the processes of BF heat under conditions of multicomponent charge, which is stipulated generally by utilization of raw materials and fuel of lower quality within the BF charge to make it cheaper. A comprehensive mathematical model of multicomponent portions of charge materials forming, their charging into the bunker of the bell-less charging facility, discharging out of the bunker and distribution on the charge surface elaborated. The elaborated intellectual system tested under real conditions of “ArcelorMittal Krivoy Rog” No. 9 blast furnace operation. The system showed effectiveness of its algorithms functioning within a sequence of test periods.

Study of gas dynamic flow regimes in RFPT technological processes

Experimental measurements of the pressure in the vacuum chamber of the RF plasma unit at various flow rates of the working gas — Argon — have been carried out, and a dynamic vacuum curve has been constructed for the system. A simulation of the flow of working gases in a vacuum chamber in a COMSOL Multiphysics package was carried out at different flow conditions in the pressure range of 1–100 Pa, the dependence of pressure on flow was established, and the calculated data were compared with experiment.

Oblique waves in steady supersonic flows of Bethe–Zel’dovich–Thompson fluids

Steady self-similar solutions to the supersonic flow of Bethe–Zel’dovich–Thompson fluids past compressive and rarefactive ramps are derived. Inviscid, non-heat-conducting, non-reacting and single-phase vapour flow is assumed. For convex isentropes and shock adiabats in the pressure–specific volume plane (classical gas dynamic regime), the well-known oblique shock and centred Prandtl–Meyer fan occur at a compressive and rarefactive ramp, respectively. For non-convex isentropes and shock adiabats (non-classical gas dynamic regime), four additional wave configurations may possibly occur; these are composite waves in which a Prandtl–Meyer fan is adjacent up to two oblique shock waves. The steady two-dimensional counterparts of the wave curves defined for the one-dimensional Riemann problem are constructed. In the present context, such curves consist of all the possible states connected to a given initial state (namely, the uniform state upstream of the ramp/wedge) by means of a steady self-similar solution. In addition to the classical case, as many as six non-classical wave-curve configurations are singled out. Moreover, the necessary conditions leading to each type of wave curves are analysed and a map of the upstream states leading to each configuration is determined.

An analytical model for characterizing the thrust performance of a Low-Pressure Micro-Resistojet

There is a clear trend towards the developments of micro-propulsion system to enhance the capabilities of nano- and pico-satellites. A promising propulsion option to meet the strict requirements of these small satellites is the Low-Pressure Micro-Resistojet (LPM) which works under rarefied gas dynamic regime. To simplify the engineering design of this propulsion system an analytical model has been developed using the fundamental physical models. This analytical model is based on the Kinetic theory of gases and the Maxwell-Boltzmann distribution of molecular velocities to describe the macroscopic flow parameters such as mass flow rate, velocity and pressure, and then to estimate the thruster performance. The equations are well known, but they are applied in this case using a particular approach in order to describe the physics behind this micro-propulsion system. Comparisons between numerical simulations using the Direct Simulation Monte Carlo method and the results of the analytical model, as well as experimental results, have been carried out. The analytical model using an accurate estimation of the transmission coefficient compared to the numerical simulation presents a maximum difference of 3%.

Modeling Plasma via Electron Impact Ionization

Variable and potential plasma applications in aerospace engineering are exemplified by ion thrusters, flow control by plasma actuator, enhanced ignition and combustion stability. The operational environments span a range from the rarefied to continuum gasdynamic regimes; however, the ionization process in practical applications is mostly by electron impact. The fundamental ionization mechanisms by electron impact consist of electron secondary mission and the cascading process. In an alternating electric field, unsteady and random micro discharges or streamers are always presented; therefore the discharge physics imposes a formidable challenge for incisive understanding. Meanwhile, the ionized species constitute hundreds of metastable chemical species; under this circumstance the physics-based modeling for analyzing the inhomogeneous medium becomes necessary. A summary of the physics-based modeling for electron impact ionization from the Boltzmann distribution equation to the inelastic particle kinetics formulation is delineated.

Introduction into MMK Blast Furnaces of an Automated System for Smelting Control, Optimization, and Prediction

Results are provided for work conducted in the Magnitogorsk Metallurgical Combine blast-furnace workshop for production satisfaction of a blast-furnace automatic control system by stagewise introduction of local systems combining into one automated system for control, optimization, and prediction of blast furnace smelting (ASCOP BF). Using mathematical models and special ASCOP BF algorithms for each blast furnace, there is continuous automatic monitoring of radial and circumferential gas distribution in the bell, circumferential gas distribution in the furnace hearth, material and thermal balances of smelting and furnace heating; optimization of the smelting gas dynamic regime, radial and circumferential gas distribution in the bell, circumferential gas distribution in the furnace hearth, smelting recovery processes, thermal state of a furnace and melting zone parameters; prediction of silicon content in cast iron. The order of conducting operations is proposed and substantiated for achieving maximum productivity and minimum coke consumption with given smelting raw material and operating conditions. It is shown that the mathematical models used in the system by the process described are ready for use in blast furnace automatic control systems already created for blast furnaces in other metallurgical enterprises in order to achieve the best smelting indices.

Use of Contemporary Information Technology for Analyzing the Blast Furnace Process

Computer implementation of mathematical models, algorithms, and computer programs is given for resolving a set of production problems in the field of blast furnace production introduced into Magnitogorsk Metallurgical Combine. Requirements are considered for the structure and architecture of a computer system for support of solutions adopted for an MES-level Blast Furnace Technologist workstation. A short description is provided for the main model sub-systems, and also assumptions made during mathematical modeling. Use of the systems makes it possible for engineering and production personnel to perform operational analysis of a blast furnace workshop situation, to resolve a number of production problems for controlling blast furnace heat, gas-dynamic, and slag regimes, and also to calculate the optimum blast furnace charge composition, which finally provides an improvement in blast furnace production technical and economic operating indices.

Pulsed plasma deposition of Fe-C-Cr-W coating on high-Cr-cast iron: Effect of layered morphology and heat treatment on the microstructure and hardness

Abstract Pulsed plasma treatment was applied for surface modification and laminated coating deposition on 14.5 wt%-Cr cast iron. The scopes of the research were: (a) to obtain a microstructure gradient, (b) to study the relationship between cathode material and coating layer microstructure/hardness, and (c) to improve coating quality by applying post-deposition heat treatment. An electrothermal axial plasma accelerator with a gas-dynamic working regime was used as plasma source (4.0 kV, 10 kA). The layered structure was obtained by alternation of the cathode material (T1 - 18 wt% W high speed steel and 28 wt% Cr-cast iron). It was found that pulsed plasma treatment led to substrate sub-surface modification by the formation of an 11–18 μm thick remelted layer with very fine carbide particles that provided a smooth transition from the substrate into the coating (80–120 μm thick). The as-deposited coating of 500–655 HV0.05 hardness consisted of “martensite/austenite” layers which alternated with heat-affected layers (layers the microstructure of which was affected by the subsequent plasma pulses). Post-deposition heat treatment (isothermal holding at 950 °C for 2 h followed by oil quenching) resulted in precipitation of carbides M7C3, M3C2, M3C (in Cr-rich layers) and M6C, M2C (in W-rich layers). These carbides were found to be Cr/W depleted in favor of Fe. The carbide precipitation led to a substantial increase in the coating hardness to 1240–1445 HV0.05. The volume fraction of carbides in the coating notably increased relatively to the electrode materials.

Software for the Raw-Materials Management System in Blast-Furnace Smelting

A description is presented of an information-modeling system developed to help optimize the composition of the charge materials and fluxes in sintering and blast-furnace smelting. The system is based on models that provide for end-to-end accounting of the sintering-machine and blast-furnace charges, calculate the technical-economic indices of blast-furnace smelting (coke rate, productivity) when there are changes in the blast parameters, the properties of the coke, and the composition of the iron-ore-bearing part of the charge, calculate the properties of the primary and secondary slags and the desulfurizing ability of the final slag, predict the sulfur content of the pig iron; model the gasdynamic regime during smelting, and diagnose the course of the smelting operation. The software that has been developed is designed to automate the work station of production personnel in the blast-furnace shop at the Magnitogorsk Metallurgical Combine.

TECHNOLOGICAL FEATURES AND SOFTWARE CALCULATIONS OF BLOWING CHARGE IN BLAST FURNACE

The article presents the technological features of the charge choice for fi lling the blast furnace. The developed complex of mathematical models and software was designed for charge calculation to fi ll the blast furnace with adjustable process of slag formation and recovery. When blowing, the fi rst portions of slag-forming and iron-ore materials were located in the furnace shaft and there was no need for gradual improvement of the ore load. The basic functional capabilities of the software allowed the following: manual maintenance (the structural characteristics of blast furnaces; the parameters of the previous blowing-in, properties of slag-forming and iron ore materials, coke, and others); the calculation of the charge for fi lling and cast iron and slag properties at user-specifi ed spending of slag-forming materials and fl uxes and blast parameters; calculation of the optimal charge composition for fi lling and blowing selection subject to the restrictions in heat, slag, gas-dynamic regimes and the quality of the cast iron; diagnosis and presentation of calculation results in tabular and graphical forms, saving them in the database.

Maximizing the Use of Pulverized-Coal Fuel in the Blast-Furnace Shop at the Mariupol Metallurgical Combine

The prerequisites for maximizing the use of pulverized-coal fuel (PCF) injected into the hearth of blast furnaces are examined for the operating conditions in the blast-furnace shop at the Mariupol Metallurgical Combine The maximum possible amount of PCF that can be used is determined based on the thermal state of the furnace, its gasdynamic regime, and the durability of the lining and the coolers in the bosh. Calculations are performed using both shop performance data and results obtained by mathematical modeling.

Improving Blast-Furnace Smelting Indices Through More Efficient Screening of Sinter Fines

Reducing the amount of fines in a blast-furnace charge significantly increases furnace productivity while also decreasing coke rate and the cost of making pig iron. The agglomeration facility at the metallurgical combine of EZRAZ ZSMK was originally designed to make one type of concentrate for blast-furnace smelting. The capacity of the warehouses where raw materials are averaged and the capacities of the equipment for crushing, screening, and delivering limestone to the facility were planned accordingly. The charge which is currently used for the sintering machines contains up to 10 iron-bearing components (concentrates, ores, additives) that differ significantly from one another in their chemical composition and physicochemical properties (granulometric composition, initial and final melting points, etc.). Irregular deliveries of iron-ore-based raw materials, the small reserves of these materials, and the inadequate storage capacity of the warehouses are adversely affecting the conditions under which the materials are averaged, thus leading to a reduction in the sinter’s mechanical strength and an increase in its content of fines. Implementation of a plan to improve the designs of the screens and screening surfaces and introduce measures to reduce the sinter’s content of fines has made it possible to lower the amount of fines in skip coke by 0.4–0.6 abs.%, improve the gasdynamic regime of the blast furnaces, increase productivity by 0.1–0.3%, and reduce the coke rate by 0.1–0.2%.

Numerical Modeling of Ion Transport in an ESI-MS System

Gas and ion transport in the capillary-skimmer subatmospheric interface of a mass spectrometer, which is typically utilized to separate unevaporated micro-droplets from ions, was studied numerically using a two-step approach spanning multiple gas dynamic regimes. The gas flow in the heated capillary and in the interface was determined by solving numerically the Navier-Stokes equation. The capillary-to-skimmer gas/ion flow was modeled through the solution of the full Boltzmann equation with a force term. The force term, together with calculated aerodynamic drag, determined the ion motion in the gap between the capillary and skimmer. Three-dimensional modeling of the impact of the voltage applied to the Einzel lens on the transmission of doubly charged peptide ions through the skimmer orifice was compared with experimental data obtained in the companion study. Good agreement between measured and computed signals was observed. The numerical results indicate that as many as 75% of the ions that exit from the capillary are lost on the conical surface of the skimmer or capillary outer surface because of the electrostatic force and plume divergence.