Abstract: This article focuses on gas flow regularity in nano-micron porous media. The flow state was judged by Knudsen number, and then the flow state chart was drawn. The flow characteristics were illustrated for different regions. The correction coefficient of permeability was improved based on the Beskok-Karniadakis model. By introducing polynomial correction coefficients, the Beskok-Karniadakis model was simplified to a binomial equation, and the values of polynomial correction coefficients were obtained by the least squares method. Compared with the Beskok-Karniadakis model, the simplified model has high accuracy. The flow rate equation in nano-micron porous media was developed based on the simplified model. The gas unidirectional seepage law was derived from indoor micro seepage experiment. The flow rate equation in nano-micron porous media agrees with experimental data. Factors influencing the gas flow rate were numerically studied by programming on the base of this model. It is found that the gas flow rate increases more and more quickly with the pressure square difference, and increases with the permeability of porous media and the Knudsen diffusion coefficient.
Abstract: To resolve the problem of high dust concentration during the process of coal cutting at fully-mechanized working faces and obtain rational dust control parameters, as well as to meliorate working conditions, considering No. 2225 working face in Xingdong Mine as a research background, numerical simulation was performed using FLUENT software to track dust movement laws during coal cutting at the fully-mechanized working face based on the theory of gas-solid two-phase flow. Compared with the actual dust concentration distribution in the mine, the simulation results are basically consistent with the actual data. The wind velocity at the fully-mechanized working face, shearer drum rotation speed, valve speed, and wall condition mainly affect the dust concentration distribution at the fully-mechanized working face. It is concluded that the dust removal effect is better when the average wind velocity is 1. 4 m·s-1, the drum rotation speed is no more than 2. 5 rad·s-1, and the valve speed is less than 1. 5 m·s-1. Meanwhile, sprinkling water, which can keep the coal wall moist, plays a significant role in capturing dust.
Abstract: In order to master the concentration distributions and diffusion laws of various components of gas in goafs, study their changes with time and obtain the reasonable parameters of goaf sealing and inerting fire-fighting technology, the concentrations of various components of gas during inert gas injection were monitored by using sampling and experiment analysis methods. Then the process of sealing and inerting in the goaf was simulated based on the permeability and diffusion theory with Fluent software. The simulation results are essentially coincident with the measured data, validating the accuracy of the simulation results. It is also found that a "Double U" ventilation system can make the airflow field distribution uniform in the goaf. The concentrations of O2, CO2 and N2 gradually reduce with the increase of distance from the working face while the concentration of CH4 radially increases from the center of the lower corner under the normal ventilation case. The concentrations of O2 and N2 gradually increase over time as the inert gas injection process go on, but the concentrations of CH4 and CO2 decrease at the same time.
Abstract: The flotation behavior of cervantite with dodecylamine (DDA) was studied. The results show that the recovery rate of cervantite reaches more than 90% in the pH range of 2. 0 to 8. 0. But it sharply decreases in the pH range of 8. 0 to 10. 0. When pH〉 10, DDA has little collecting capacity on cervantite. The flotation solution chemical analysis of dodecylamine indicates that dodecyl-amine cations are the main components of the cervantite collector. The electronic structures of cervantite crystals and dodecylamine ions and molecules were studied using the density functional theory. The adsorption behaviors of dodecylamine ions, dodecylamine mole-cules, and water molecules were simulated. It is found that the adsorption energy order of these adsorbents on cervantite surfaces is DDA 〉 H2 O 〉 DDA+. DDA+ can remove hydration films on cervantite surfaces to make cervantite hydrophobic. DDA+ adsorbs on cer-vantite surfaces mainly by physical adsorption.
Abstract: To study the effect of silicate minerals in tailings on autoclaving construction materials, the autoclaving reaction activity of hornblende, labradorite, albite, and biotite was analyzed by X-ray diffraction, thermogravimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy, and infrared spectrometry. The results show that at 180℃ for 8 h, labradorite and albite have autoclaving reaction activity, but hornblende and biotite do not. Autoclaving products in the labradorite system contain hibschite and clinotobermorite, while in the albite system contain tobermorite. These products connect together, which helps to improve structural compactness. Na exists in tobermorite minerals, indicating that the minerals have the function of alkali binding.
Abstract: Mineralogical studies on catarinite raw ore and reduced samples at different temperatures were carried out, and phase transformation was explored in the catarinite selective reduction roasting process. The results show that the main metal minerals in the catarinite are limonite and then hematite. The distribution of Ni in Mn-free iron minerals is relatively homogeneous, but it is relatively concentrated in Mn-contained iron minerals, and Ni is associated with Mn. Reduction, phase transformation, migration and enrichment of Fe, Ni and Co gradually occur in the process of catarinite reduction roasting with increasing temperature, so the selective reduction roasting temperature should be controlled strictly. To reduce Ni, Co and Fe selectively and form a more Ni and less Fe alloy phase and magnetite, 750℃ is a proper roasting temperature, at which the formed alloy phase contains Ni of 55. 55%, Co of 9. 86% and Fe of 33. 99% averagely, the metal conversion rate of Ni is 88. 49%, and the iron oxide is mainly magnetite.
Abstract: Center segregation with different solidification structures was investigated in pipeline steel. Macrostructure photographs show that center segregation in continuous casting slabs is composed of many semi-macro segregates, which are relatively independent and separated spot-like segregates with different sizes. The features of semi-macro segregation are different for different solidification structures. Chemical analysis shows that negative segregation is formed across the equiaxed zone in the center of the slab, while positive segregation is observed in the center of the slab surrounded by columnar crystals. It is revealed that the semi-macro segregation area in the center of the slab increases with the increase of the maximum segregation ratios of C and Mn. However, compared with the method of segregation area measurement, only local segregation could be obtained by chemical analysis, and it is obvious that the method of segregation area measurement is more helpful to industrial practice. Furthermore, the segregation area with different solidification structures under different superheats was calculated. The results indicate that as the soft reduction technology is applied reasonably, columnar crystals in the center of the slab are more advantageous to the reduction of segregation area, and finally would be better for the improvement of center segregation.
Abstract: Based on measured data of wide and thick slab sticking breakout in a domestic iron and steel company, the influence of slab size, casting speed and mould level on the sticking breakout was studied. The variation of mould heat flux was investigated during the sticking breakout. Some possible reasons were discussed for the sticking breakout in view of casting parameters and mould heat flux.
Abstract: Taking 12Cr-0. 5Ti-1W gas atomized powders and nona-Y2O3 as pre-alloyed powders, 12Cr oxide dispersion strengthened (ODS) ferritic steel was fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP). The properties of the ferritic steel were improved by forging and heat treatment. Nano-oxide particles were observed in the microstructure by transmission electron microscopy, and these precipitated particles were identified to be Y-Ti-O complex compounds by energy dispersive X-ray spectroscopy. The mechanical properties of the ferritic steel were analyzed by tensile strength test and ultrasonic non-destructive test.
Abstract: The effects of carbon and nitrogen contents on the characteristics and forming mechanism of precipitates in as-cast and aged 18Mn18Cr high nitrogen steels were investigated by optical microscopy, scanning electron microscopy, electron probe micro-analysis, transmission electron microscopy and thermodynamics calculation (Thermo-Calc). It is found that with the decrease in mass ratio of C to N, the precipitate is Cr23C6 phase, σ phase and Cr2N phase in the as-cast steel in turn. The precipitation of Cr23C6 and Cr2N phase increases as the C or N content increases. C and N contents influence the solidification mode of the tested steel and the eutectoid decomposition of the unstable ferrite phase. The solidification mode of 18Mn18Cr0. 44N steel is an AF mode, and the eutectoid decomposition reactions corresponding to the C contents of 0. 025% and 0. 16% are δ→σ + γ2 (0. 025% C) and δ→γ2 + Cr23 (CxNy)6 (x/y〉 1) (0. 16% C), respectively. The solidification mode of 18Mn18Cr0. 72N steel is an A mode, and a little granular Cr2N phases precipitate on grain boundaries. Only laminar Cr2N0. 39C0.61phase exits in the aged steel, and with the increase of C + N content, the volume fraction and lamellar spacing of the precipitates increase, but the incubation time decreases.
Abstract: The fatigue properties of 2 mm-thick Ti-microalloyed high-strength steel produced in a CSP line was studied by the up-down method. It is found that the tensile strength of the steel is 830 MPa, the fatigue strength is 685 MPa, about 0. 83 times as large as the tensile strength, and the elongation is 18. 8%. The S-N curve of the steel was drawn out and the relationship between the maximum stress and fatigue life was fitted. The cracking mechanism was analyzed by scanning electron microscopy. The crack source, expansion region, and eventual failure region appears significantly in the microscopic structure. Fatigue cracks initiate from microcracks on the strip surface. Microcosmic fatigue striations, secondary cracks, and macroscopic fatigue bay ridges are observed in the fatigue extension region. The eventual failure region meets the characteristics of tear edge morphology along with dimples.
Abstract: Fe-Si composite coatings were prepared by nano-composite electroplating in a static magnetic field parallel to the electrode surface. The effects of magnetic flux density and current density on the cathode current efficiency and silicon content in the coatings were studied. The coatings were characterized by scanning electron microscopy and energy dispersive spectrometry. It is found that the cathode current efficiency first increases and then decreases with increasing magnetic flux density. The mass fraction of silicon in the coatings reaches its maximum value of 20. 17% at 0. 2 T, which increases by 10. 4% compared with that without any magnetic field. In addition, the smooth surface morphology of the coatings turns into "mountain ranges", whose directions are the same to the direction of magnetohydrodynamic convection (MHD). More and longer "mountain ranges" appear with increasing magnetic flux density. Owing to MHD effect, the magnetic field also influences the surface morphology of hydrogen pores and promotes the evolution of hydrogen.
Abstract: The microstructure and microsegregation of nickel-based superalloy Inconel 617B ingots produced by vacuum induction melting and electroslag remelting were studied by optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Their kinetic homogenization curves were calculated by Dictra software through the residual segregation parameter model. Based on the theoretical results, seven homogenizing treatments were tested. Microstructure analysis and thermal compression test with a Gleeble 1500 machine were used to verify the effect of homogenizing treatment. It is found that dendrites and element segregation exist in the ingots, and Mo and Ti are the principal segregated elements. The main precipitated phases in the ingots are different kinds of primary carbides which tend to symbiotic growth. After homogenization at 1210℃ for 48 h, this segregation can almost be eliminated, the phase of intragranular carbides dissolves to the matrix, and the ingots exhibit excellent workability.
Abstract: Aluminum matrix composites were prepared using an in-situ reactive near-liquidus casting technique in two systems of Ti-C-Al and Ti-C-Al-CuO. Their microstructure was studied by optical microscopy, scanning electron microscopy and X-ray diffraction. Thermodynamic analysis on the reaction in the two systems was carried out. The effect of CuO on the self-propagating reaction process of the Ti-C-Al system was discussed, and a kinetic model was set up. It is found that in the self-propagating reaction process of the Ti-C-Al system, the reaction between CuO and Al is able to enhance the adiabatic temperature of the system and provide the system with sustaining heat, making the self-propagating reaction more remarkable and more completed. As a result, blocky Al3 Ti mesophase is extremely decreased, and the microstructure of the composites is optimized.
Abstract: WO3 nanorod arrays were prepared on indium tin oxide (ITO) substrates by hydrothermal synthesis with Na2WO4·2H2O as a raw material and NaCl as an additive. The nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The effects of pH values on the morphology, size, and orientation of products were studied. The results show that the single crystalline WO3 nanorod is hexagonal. When the pH value of the precursor solution increases, WO3 nanorod bundles parallel to the substrate turn into nanorod arrays vertical to the substrate. In addition, two different orientation WO3 nanorod structures were investigated by photocatalytic degradation of methyl blue solutions. It is found that the photocatalytic property of WO3 nanorod arrays is better than that of WO3 nanorod bundles.
Abstract: The gas distribution behaviors of oxygen blast furnaces with shaft gas injection were experimentally studied using a two-directional cold model. The effects of total gas flow rate in the shaft, auxiliary tuyere diameter and location, and the ratio of injected gas flow rate to total gas flow rate in the shaft on the injected gas distribution were investigated in detail. The results show that the injected gas distribution in the shaft is almost dominated by the ratio of injected gas flow rate to total gas flow rate in the shaft, while the influences of total flow rate and auxiliary tuyere diameter are little. Meanwhile, the influence of radial eddy diffusion is also little in the process of gas rise in the shaft. According to isoconcentration distribution curves from experimental data, the injected gas distribution in the shaft is divided to two dissimilar zones, a main flow region of injected gas and a main flow region of upward gas. Furthermore, the penetration equation of injected gas at the injection level is deduced through the regression analysis method. In addition, the auxiliary tuyere installed in the lower part of the shaft is advantageous for iron ore indirect reduction in the shaft.
Abstract: A shape control strategy by bending force combination adjustment for 6-hi cold rolling mills was proposed to solve the theoretical insufficiency of 4-order shape defect control by two kinds of bending forces. A roll-strip coupling model was established with Marc finite element simulation software, and the difference of shape control characters was analyzed between work roll bending force and intermediate roll bending force. Two methods for implementing the shape control strategy, which are the on-line closed-loop control model and the on-line setting parameter adjustment method based on bending force combination coefficients, were introduced by theoretical derivation. It is proved by field application that with the shape control strategy, the difference of shape control characters between work roll bending force and intermediate roll bending force is fully utilized and the combination adjustment is realized to precisely control 4-order shape defects, which perplex production for a long time.
Abstract: Numerical simulation was performed to study the internal mixing chamber flow field of a premixed abrasive water jet descaling nozzle by FLUENT software based on a CFD (computational fluid dynamics) multiphase flow mixture model. The effects of abrasive supply modes as well as different parameters under bilateral high-pressure water entrances such as abrasive and high-pressure water inlet diameters, high-pressure water inlet location and angle, and contraction cone angle on the flow field uniformity were analyzed to obtain reasonable structure parameters. Numerical calculation results show that the mixing uniformity of the internal mixing chamber for the abrasive entering by the central entrance mode is superior to that by the bilateral entrance mode at constant entrance velocity. The jet velocity out of the internal mixing chamber increases with the increasing abrasive and high-pressure water inlet diameters, but the outlet abrasive concentration increases firstly and then decreases as the high-pressure water inlet diameter increases. The location of bilateral high-pressure water entrances has relatively little effect on the mixing uniformity of the internal mixing chamber. When the mass flow ratio of abrasive to high-pressure water is about 3:4, and when the high-pressure water inlet angle and contraction cone angle are set at 30°, a relatively uniform flow field can be obtained.
Abstract: A two-dimensional isotropic plate model with an embedded horizontal crack was established. Finite element analysis with absorbing boundary condition was employed to simulate the experimental pulse-echo mode to obtain ultrasonic data. The effect of crack depth on the wave propagation was studied and the spectra of different backwall echoes were further extracted. A relationship was determined between ultrasonic attenuation due to the crack and frequency. Finally, a method was proposed for identifying subsurface cracks based on the spectra of backwall echoes.
Abstract: In order to suppress the reflected acoustic waves of wide band noise in a narrow and enclosed space, this article introduces a reflected acoustic wave suppression method based on the cepstrum clip. In the proposed method, firstly, the reflected part in the cepstrum of noise is divided by the environmental impulse response duration; secondly, abnormal points in the reflected part are determined by the theory; finally, the abnormal points are assigned to normal values again, thereby the reflected components are suppressed without breaking the direct components of noise. To validate the proposed method, experiments were performed in an ordinary room, which is a weak reflection environment, and in an experimental module, which is a strong reflection environment. Experimental results show that the proposed method can effectively suppress the reflected acoustic waves. The error of sound field reconstruction brought by the reflected acoustic waves is decreased from 90% to 35%, indicating that the proposed method improves the accuracy of sound field reconstruction.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
