Abstract: Based on the molecular kinetic theory, the gas seepage law was analyzed in shale gas sediments with nanopores. The motion equation and transport mathematical model of shale gas were established which were suitable for multi-scale media. The pressure distribution formula under radial flow was derived, and a new method to calculate the control area of shale gas wells was formed. The non-linear productivity equation of fractured wells was presented with three-region division. Some parameters, such as production pres-sure difference, fracture half-length, fracture conductivity and diffusion coefficient, which can influence the gas well production were analyzed according the numerical calculation of the Newton iteration method. It is shown that the gas well production increases with increasing diffusion coefficient, and the contribution of diffusion effect to production should not be ignored for shale gas reservoirs with nanopores. In a certain reservoir and production conditions the gas well production increases with the increase of fracture half-length, but the increase rate is slower. Thus there is an optimum combination of parameters for shale gas development.
Abstract: According to the mass conservation law, a dynamic network model which considers interaction between solid walls and liquid molecules was established. This model is on the basis of solid-liquid intermolecular force and in combination with the distribution characteristics of pore throats in porous media. The change in pore pressure at different time steps was simulated through the model. The influences of solid-liquid intermolecular force, pore throat radius and wettability on the saturation distribution of remaining oil and the permeability curve of water flooding phase were analyzed. The results show that when considering solid-liquid intermolecular force the saturation of residual oil increases, thus interaction between rock and fluid molecules cannot be ignored in the study of porous flow in porous media.
Abstract: The effects of pulp pH values, dispersants and auxiliary collectors on direct reverse flotation of carbonate-containing iron ores were explored. Floatation experiment results show a sharp increase in iron grade as the pH value raises from 11.0 to 11.8, and the maximum grade can be obtained at pH 11.8, after which the iron grade has almost no change. When the pH value is 12.0, sodium tripolyphosphate is a kind of effective dispersant and sodium dodecyl sulfate is an effective auxiliary collector of KS-Ⅲ, both the iron recovery and grade increase with the action of sodium dodecyl sulfate or sodium tripolyphosphate. Theoretical calculations indicate that the floatation results are related to the solution chemistry of siderite and interactions between particles. Structure-activity calculations of collectors show that sodium dodecyl sulfate has perfect selectivity, emulsion and solubility.
Abstract: The melting performance of an Al2O3-CaO-MgO ternary slag system and the effect of added fluxes on the melting point of the slag system were theoretically analyzed by using Equilib and Phase Diagram modules in thermodynamic software FactSage. The melting temperature of the slag system from production was measured. It is found that the melting point of the slag system decreases first and then increases with increasing w(Al2O3)/w(CaO) ratio, and it reaches the lowest value when w(MgO) is 4% to 5%. At the w (Al2O3)/w(MgO) ratio more than 3 and w(CaO) less than 30%, the melting point decreases with increasing w(CaO). When 2〈w (Al2O3)/w(CaO) 〈2.5 and w(MgO) is 15% to 18%, the melting point can decrease about 100℃ with the addition of 2.29% AlCl3, 4.86% Fe2O3 or 4.77% Na2O in the slag system.
Abstract: The morphology of the reduction products of Fe-Cr-O systems by C at different temperatures and time intervals was studied in this paper. The samples include two systems of FeCr2O4 +C and Fe2O3 +2Cr2O3 +C. It is found that the reduction degrees of the two samples increase with increasing temperature, and the reduction degree can be above 90% when the reaction is close to balance. The reduction processes of FeCr2O4 and Fe2O3-Cr2O3 are similar and the final reduction products are composed of Fe-Cr-C alloys and metal carbides (mainly Cr7C3). A method was proposed to estimate the contents of Fe-Cr-C alloys and metal carbides in the final reduction products, and the estimated results agree with the calculated data. It is shown that the content of Fe-Cr-C alloys increases while the content of metal carbides decreases with increasing temperature, and the composition of Fe-Cr-C alloys varies with temperature.
Abstract: Solidification of hypereutectic high-chromium cast iron samples near-liquidus melted was treated with electric current pulse (ECP). The effects of ECP parameters such as electric voltage and pulse frequency on the solidification microstructure were investigated during the treatment. It is found that increasing the pulse frequency or electric voltage is helpful to carbide refinement and granulation in the cast iron. The increase of pulse frequency promotes the precipitating of a large number of fine granular primary carbides and the occurrence of a divorced eutectic reaction, which lead to the decrease in number of lamellar eutectic carbides. The increase of electric voltage contributes to the primary carbides refining and granulating as well as the lamellar eutectic carbides shortening. An excessive voltage value can also be favorable to the occurrence of a divorced eutectic reaction and the formation of additional primary carbides.
Abstract: The high temperature ductility of samples, taking from a Q345B continuous casting slab in the transverse direction, drawing direction, vertical direction and at the central part, as well as an AH32 continuous casting slab at the surface and 1/4 thickness position, was investigated by using a Gleeble-1500 testing machine. The fractographs and microstructures of high-temperature tensile samples were observed by optical microscopy and scanning electron microscopy. Experimental results show that the high temperature ductility below 950℃ changes little between 4 groups of different samples from the Q345B slab, but the variation tendencies of high temperature ductility above 950℃ are greatly different. The changes of high temperature ductility of 3 groups of samples from the AH32 slab at the surface are the same, and the reduction of area has little fluctuation. Whereas the high temperature ductility of 3 groups of samples at the 1/4 thickness differs entirely from that at the surface, and the reduction of area appears fluctuant greatly. The reason is that microcracks, composition segregation, porosity and looseness occur more easily in the columnar crystal zone of sampling than in the equiaxed crystal zone of the surface.
Abstract: Using Si-Mn dual-phase (DP) steel as a reference, the microstructural evolution and dynamic mechanical properties of Si-Mn transformation-induced plasticity steel (TRIP) steel at the 600 MPa level and TRIP steel offering the ultimate tensile strength (UTS) level up to 1000 MPa containing Al and Ni were investigated under high strain-rate deformation. It is found that the tensile strength increases with increasing strain rate and the fracture elongation increases due to adiabatic heating in the DP steel. In the TRIP steel, the tensile strength increases with increasing strain rate while the fracture elongation decreases at first and then increases. However, the ductility of the TRIP steel is relatively low at high strain rate since the gradual transformation effect of retained austenite is inhibited. The adiabatic heat produced during high strain-rate deformation is higher in the TRIP steel than in the DP steel, and it is suggested that this extra heat originates from the latent heat of martensitic transformation in the TRIP steel during dynamic deformation.
Abstract: The segregation characteristics of Ni, Mn, P and C atoms at the phase boundaries of AlN/α-Fe matrix, Cu-rich precipitate/α-Fe matrix and AlN/Cu-rich precipitate in reactor pressure vessel (RPV) model steel were investigated by atom probe tomography (APT). RPV model steel specimens were heat treated at 890℃ for 0.5 h followed by water quenching and aging at 500℃ for 20 h. The results demonstrate that Ni, Mn, C and P atoms do not segregate to the Cu-rich phase/AlN phase boundary, only segregate to the AlN/α-Fe and Cu-rich nanophase/α-Fe phase boundaries, and their segregation characteristics have no significant differences. It is also observed that Mn has a larger segregation tendency than Ni, and C has a larger than P at both different phase boundaries of Cu-rich nanophase/α-Fe and AlN/α-Fe.
Abstract: Based on the need for pipeline steel in the oil and gas industry of China, a novel 2% Cr pipeline steel with good matched strength and toughness was developed through a reasonable thermomechanical control process (TMCP). Its mechanical proper-ties and microstructure were studied preliminarily and the results show that the 2% Cr pipeline steel mainly containing acicular ferrite and a few polygonal ferrites has a better combination of strength and toughness. The corrosion resistance of the 2%Cr pipeline steel was evaluated in the CO2 top-of-the-line corrosion environment in submarine wet gas pipelines which was simulated with a high temperature and high pressure condensation autoclave. Compared with traditional pipeline steel, adding 2% Cr makes obvious changes of corrosion behavior and a continuous and compact amorphous film with Cr enrichment forms, thus improving its CO2 corrosion resistance.
Abstract: This article reports fracture in hard films on a soft substrate under conical indentation. A diamond-like carbon (DLC) film was deposited onto a poly-ether-ether-ketone (PEEK) substrate using plasma chemical vapor deposition. Nanoindentation was performed on the film surface, in the meanwhile, load and depth data were recorded, and ‘pop-in’, correlated with crack formation, was found in load-depth curves. Ring cracks and radial cracks in the film were observed by scanning electron microscopy and focused ion beam method after indentation. Finally, finite element analysis using cohesive elements was conducted to study the stress distribution of the hard film/soft substrate. It is found that ring cracks in the thin film are induced by high tensile radial stress on the film surface outside the contact region of the indenter, while radial cracks are caused by high tensile stress on the thin film near the interface. The results also show that the radius of ring cracks increases with the number of ring cracks, which agrees well with experimental observations.
Abstract: PVA hydrogel artificial nucleus materials were prepared by a freeze-thaw cycle method, their compressive creep properties and viscoelastic model were studied in deionized water and different simulated body fluids, including saline and Hanks solutions. PVA hydrogel exhibits very good viscoelastic properties in the different simulated body fluids, the speed and deformation to reach the creep equilibrium are related to ion content in the fluids. Isochronous lines show that the mechanical behavior of PVA hydrogel accords with the linear viscoelastic behavior. The Kelvin-Voigt model succeeds in simulating the creep behavior of PVA hydrogel. Fitting results show that some salt ions in the body fluid inhibit the movement of small-size cells inside of PVA hydrogel, thereby extending the creep equilibrium time. Na+ in the body fluid can promote the movement of large-size cells inside of PVA hydrogel and makes it quickly to reach the creep equilibrium. These meet the clinical requirements.
Abstract: Epoxy resin composites filled with high-alumina fly ash cenospheres were prepared in this paper. Their impact strength and erosive wear behaviors were investigated by impact test and erosive wear test. Polyamide 650 was determined as an ideal curing agent to epoxy resin according to the erosion wear mechanism, wear resistance and impact performance. Silane coupling agent improves the compatibility of the cenospheres and the epoxy resin matrix, which effectively increases the erosion resistance of the composites. When the mass fraction of the cenospheres is less than 3%, the impact strength and the erosion resistance of the composites does not change obviously. When the mass fraction of the cenospheres is 3%, the impact strength reaches maximum and the erosion resistance also increases obviously. And when the mass fraction of the cenospheres is 4%, the erosion resistance is the best. As a result, the appropriate mass fraction of high-alumina cenospheres was determined ultimately to be 3% to 4%.
Abstract: A general model of pulverized coal combustion ratio was put forward, which can calculate the kinetic parameters and combustion ratio based on coal industrial analysis. The accuracy of this model was verified by comparing with previous experimental data. Some factors influencing the coal combustion ratio were discussed. It is found that during the process of pulverized coal injection, the pulverized coal particle can reach the velocity of hot blast within 2 ms. In the blowpipe, due to the pulverized coal particle with short residence time and lower temperature, combustion reaction does not occur. When the pulverized coal particle enters into the raceway, the volatile is released instantly. The smaller the coal diameter is, the earlier the volatile will be released. The coal combustion ratio can be improved by decreasing the coal diameter or increasing the oxygen enrichment. When the oxygen enrichment increases 1%the combustion ratio increases about 2%. With increasing coal injection rate, the coal combustion ratio decreases. Therefore, when the coal injection rate increases, we should increase the oxygen enrichment and decrease the particle diameter appropriately to maintain the high combustion ratio.
Abstract: According to flue gas desulfurization processes with activated carbon, several factors affecting the catalytic reaction rate of activated carbon for flue gas desulfurization were investigated on the basis of the experiment of adsorbate concentration curves along the bed. It is found that SO2 concentration and CO2 volume fraction have significant influences on the catalytic reaction rate, and SO2 concentration is the primary factor. With increasing SO2 concentration, the catalytic reaction rate increases significantly, but it does not increase at high SO2 concentration. While the CO2 volume fraction increases from 0 to 15%, the catalytic reaction rate decreases by 30% linearly, indicating that CO2 plays a linear inhibition role in the catalytic reaction. The flue gas velocity between 0.14 m·s-1 and 0.3 m·s-1 has no significant effect on the catalytic reaction rate.
Abstract: Based on the characteristic of variable gauge rolling and the definition of forward slip, a forward slip theoretical model was proposed in this article. A finite element model was also established with MARC software. The rolling processes of four different variable gauge strips were numerically simulated at the rolling friction coefficient of 0.08 and 0.1. In addition, the total amount of forward slip was measured by an experimental rolling approach. After comparison and analysis, it is found that there is little difference between the value calculated by theoretical forward slip model and the one simulated by finite element method. The difference is less than 0.005. Differing from stable forward slip in tradition constant thickness rolling, the forward slip fluctuates from 0.02 to 0.10 in the variable gauge rolling process. The increase of reduction rate in the variable gauge zone leads to a higher forward slip. A smaller slope of the variable gauge zone and the low friction coefficient result in a better rolling stability and a smaller fluctuation of forward slip. The experiment of TRB rolling also verifies the accuracy of the theoretical forward slip model for variable gauge rolling. The large tolerance between the measured value and the calculated one in thinning rolling is probably caused by the strain condition of deformation area and the increasing slip tendency.
Abstract: Based on the generating and extrusion theory, relative sliding between tooth profiles during gear roll forming process was solved by using the trapezoid area approximately instead of the rolled gear tooth grown area. The shear friction direction on the tooth profiles was analyzed from the relative sliding state. The influence of the relative sliding on the metal flow direction on gear profiles was verified through numerical simulation and experiment. It is verified that metal pulling on the rolling profiles is consistent with the shear friction direction.
Abstract: The temperature of gear systems was measured with a closed power flow gear test rig. It is the first time that the temperature fields of gear systems were solved by combining finite element method and thermal elastohydrodynamic lubrication method. To get the convection heat transfer coefficient accurately, the viscosity-pressure-temperature equation and the density-pressure-temperature equation were introduced to finite element analysis. The highest temperature and flash temperature of each point in the meshing line and their distribution laws along the line of action were obtained with the bulk temperature solved with finite element method as the initial temperature of the thermal elastohydrodynamic lubrication calculation. The results show that the bulk temperature solved with finite element method is consistent with the test results. The flash temperature distribution calculated with thermal elastohydrodynamic lubrication method is close to the ISO flash temperature. With increasing modification coefficient, the highest bulk temperature area transfers from the dedendum to the addendum.
Abstract: Multivariate time series collected by industrial monitoring systems often have problems such as numerous raw data, repeated segmentation results, redundant intersections and blurry boundaries in the process of using data mining technologies to acquire internal existing unknown patterns, leading to unsatisfied mining results when the dataset involves mutation variables or inferior relevance among the data. To resolve these problems, this article introduces a new multiple time sequence clustering algorithm. Experimental results show that this algorithm can overcome the shortage that the accuracy of clustering is often affected by initial values in the Gath-Geva algorithm. It can exhibit the potential variation of raw data and thus efficiently deal with segmentation in multivariate time series to get ideal mining results.
Abstract: MIDAS GTS software was used to build a 3D finite element model to analyze the influences of such factors as excavation depth, pile diameter, pile spacing, pipeline-to-pile distance, pipeline buried depth and soil elastic modulus on buried pipelines. It is found that the horizontal and vertical displacements of pipelines at the corner of the foundation pit are about 1/2 of those at its center. The maximum horizontal displacement happens when the pipeline buried depth is 1/3 of the foundation pit, and the vertical displacement decreases with increasing pipeline buried depth. When the pipeline diameter increases from 0.6 m to 1.2 m, the horizontal displacement changes little, but the vertical displacement decreases to half of the original. As the soil elastic modulus increases, the medium displacement of pipelines decreases obviously, and the horizontal displacement is about 4 times as large as the vertical displacement.
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
