Abstract: Aiming at the problem that fluid flow in nano/micro-size tubes deviates from the Hagen-Poiseuille law but the mechanism remains unclear to date, this paper focuses on fluid flowing in a nano/micro-size circular tube considering the weak compressibility of the fluid and the tube wall action. The tube wall action was introduced into the momentum equations as a wall force, the hydrodynamic vorticity-stream equations were derived, and the first-order perturbation solutions of pressure and velocity were obtained. It is found that there exists zero-order radial pressure. Due to the influence of wall-fluid interaction, the first-order radial pressure increases and the first-order velocity decreases. The dimensionless volume flow rate deviates from an uncompressible fluid due to the compressibility of the fluid and the tube wall force. The deviation of the dimensionless volume flow rate from Poiseuille flow increases with the increasing of compressible coefficient and ion concentration in the liquid acted with the tube wall, and increases with the decreasing of the tube diameter. The liquid cannot flow when the tube diameter is less than a certain size. This paper reveals that the mirco-scale effect of nano/micro-size is resulted from the compressibility of the fluid and the tube wall force together.
Abstract: A comprehensive research method composed of theoretical analysis, physical simulation and engineering practice was conducted to analyze the impact effect caused by thick hard roof group structure breaking. Some results were obtained such as the main influencing factors related to impulsion pressure, the main roof weighting characteristics and the reasonable supporting strength of the roof group structure. It is shown that impact load caused by layered hard roof group structure breaking will lead to severe concussion with scarcely attenuation. The roof weighting on the workface is affected by a combined effect of dynamic load and static load resulted from layered hard roof group structure breaking. The impulsion pressure strength is associated to roof thickness, rock traits, and rock joints and weak surfaces. For the similar roof strata, the impact effect is more severe as the roof is thicker, but the thick caving roof will be helpful for buffering the impact of the upper overburden strata. A field test was conducted in Datong area which is mining under the hard roof group structure. According to selecting the high strength supports of ZF15000/28/52 in the fully mechanized caving face to ensure safe mining before and after the first critical roof breaking, and taking the auxiliary control of hydraulic fracturing in the upper critical roof, the strong pressure has been effectively slowed.
Abstract: Metallization pellets were prepared from silicon-magnesium-type nickel laterite ore through metallization roasting and smelting process. Orthogonal experiment was carried out to investigate the effect of control parameters on the experimental results. A nickel-iron alloy was extracted from the metallization pellets after 30 min of smelting at 1 500℃. It is shown that C/O molar ratio has prior influence on the selective reduction process, followed by roasting temperature, roasting time and basicity. The nickel grade of the nickel iron alloy can be controlled at 19% in the extraction process by governing the manipulated factors. The sulphur and phosphorus distribution ratio increases when the basicity increases from 0.8 to 1.2. The metallization pellets and slag were microscopically analyzed by X-ray diffraction and scanning electron microscopy. The results show that the added limestone reacts rapidly with the complex ore to produce nickel oxide and iron oxide, and thus, promotes the reduction rate. When the amount of limestone is insufficient, little amount of iron in the form of hematite exists in the metallization pellets which have the metallization rate of 70%.
Abstract: Taking the heating process of recycling-gas for oxygen blast furnaces as a research background, carbon deposition behavior in heating at higher CO and H2 volume fractions was investigated under a laboratory condition. The results indicate that temperature and CO2 volume fraction are important factors for carbon deposition. In the temperature range of 300℃ to 700℃, the carbon deposition rate increases with the increase of temperature below 500℃, but deceases when above 500℃. The carbon deposition includes CO decomposition and carbon deposition reaction by the hybrid of CO and H2, each possible role of which was analyzed through comparing the thermodynamic theory and experimental phenomena in the carbon deposition. The morphology of deposited carbon and the carbon deposition behavior in heating from 500℃ to 700℃ were investigated by scanning electron microscopy. In addition, the carbon deposition rate decreases gradually with the increasing of CO2 volume fraction at 500℃ and 600℃, and this inhibition effect on the carbon deposition behavior is greater at 500℃.
Abstract: The diffusion couple method was used to study the solid-state reaction of the Fe2O3-TiO2 system in the temperature range of 1323 K to 1473 K in argon. The microstructure of the diffusion couple and the diffusion concentration profiles of Fe and Ti were determined by electron probe microanalysis (EPMA). According to kinetic analysis, this solid-state reaction is controlled by the diffu-sion of Fe, Ti and O ions. The inter-diffusion coefficient, which increases with the increasing temperature and concentration of Ti ions, was calculated by the Boltzmann-Matano method, and its order of magnitude is in the range of 10-13 to 10-10 cm2·s-1. The diffusion activation energy (about 356.06 kJ·mol-1) of the system in argon is much bigger than that in air, which indicates that the partial pres-sure of oxygen in atmosphere has important effect on the reaction mechanism of the system.
Abstract: Theoretical calculations by FactSage software and melting experiments were performed to systematically study the melting temperature characteristic of a CaO-FeO-Al2O3-SiO2 fluoride-free slag system used for hot metal dephosphorization pretreatment. Three influence factors of the melting temperature of the slag were researched which were the slag's binary basicity, the mass fractions of Al2O3 and FeO. The results show that the mass fraction of FeO has the greatest impact on the melting temperature of the slag among three factors. The obtained best proportion of the slag is the binary basicity of 5.5, 10% Al2O3 and 45% FeO. Under the experimental conditions, the melting temperature characteristic of the optimal slag can meet requirements for hot metal dephosphorization pretreatment.
Abstract: A novel hybrid LES-RANS (large eddy simulation-Reynold average Navier-Stokes) turbulent model was introduced to simulate fluid flow in a mold. The model employs the method of grid filtering which calculates the Navier-Stokes equation directly for large-scale eddies and calculates the standard k-ε equations for small-scale fluctuations by modifying the turbulent viscosity coefficient to simulate the flow field of molten steel. The modified eddy viscosity in the LES-RANS model can avoid the excessive diffusive nature of the RANS model and capture the transient features of turbulent flow. In this work, turbulent flow in a liquid metal (GaInSn) model of continuous casting was measured by ultrasonic Doppler velocimetry (UDV). It is shown that compared with the RANS model, the results of the LES-RANS model are more identical with measured data, so the LES-RANS model can more accurately predict the turbulence structure. The characteristics of transient flow in the mold show that bias flow at the two sides of the nozzle changes periodically and the period is about 5 s.
Abstract: Based on mass conservation in a typical micro-solidification volume element combining with previous work, a semi-analytical model of microsegregation was established for binary alloys with dendritic solidification. The effects of back-diffusion and coarsening on microsegregation are both considered in the semi-analytical model, and the coarsening of arm spacing is directly calculated to make the semi-analytical model more precise. The semi-analytical model will be simplified to the BF model or the Mortensen model when back-diffusion or coarsening is considered only, respectively. The diffusion model and the coarsening model separately represented by the BF model and the Mortensen model are well unified by the semi-analytical model. Moreover, the semi-analytical model can be extended to multicomponent alloys. The Fe-C-X(Si, Mn, P, S) alloy was taken as an example to elaborate the solving process. The eutectic fractions of the Al-4.9%Cu alloy and the zero strength temperature (ZST) and zero ductility temperature (ZDT) of carbon steel Fe-C-X(Si, Mn, P, S) during solidification can be well predicted by the semi-analytical model.
Abstract: The microstructure and mechanical properties of 0.12C-0.78Si-1.42Mn-0.74Al-0.32Mo steel under four different multi-pass deformation and controlled cooling after rolling were studied by using of a physical simulation system. The results show that different multi-phase structures (ferrite/bainite and bainite/martensite) can be achieved in the steel under multi-pass deformation at high temperature through the physical simulation system and controlling cooling treatment. The yield strength, tensile strength and total elongation of the steel with the ferrite/bainite structure are 388~558 MPa, 681~838 MPa, and 15%~27%, respectively; but the yield strength, tensile strength, and total elongation of the steel with the bainite/martensite structure reach 746 MPa, 960 MPa, and 19%, respectively.
Abstract: Variations in the recrystallized texture and microstructure of cold-rolled 430 stainless steel during isothermal annealing were investigated on a Gleeble-1500 thermal-mechanic simulator at 750, 800, 825 and 850℃, and the evolution of main textures was analyzed quantitatively. As annealing proceeds, the intensity of α-fiber orientation components decreases, but the intensity of γ-fiber components increases slightly and maintains at a higher value. The volume fraction of{111} and{112}<110> decreases as recrystallization proceeds, while the volume fraction of{100} and random orientation textures increases. Compared with the cold-rolled state, it is observed that the volume fraction of main textures has greater changes in annealing at low temperature than at high temperature. Finally, variations in the volume fraction of{111},{112}<110>,{100} and random orientation textures during recrystallization were described by a JMAK kinetics model.
Abstract: The thermal expansion properties of steels with different chemical compositions were precisely measured at temperatures from 30 to 1150℃ with a NETZSCH DIL 402C dilatometer. The curves of thermal linear expansion and instant linear expansion coefficient versus temperature were plotted from measured data. Quantitative analysis and comparison results show that carbon content has different influences on the thermal linear expansion and instant linear expansion coefficient of steels in the three temperature ranges of low temperature, solid phase transformation and austenite phase. Thermal expansion caused by the heat effect, which is basically the same for different steels, is dominant in the whole temperature range. The shrinkage of samples caused by phase transformation, which decreases with increasing carbon content, accounts for about 16% of the total absolute amount of thermal expansion, leading to the different expansions for the three steels.
Abstract: The effect of thermal aging at 400℃ for a longer time on the pitting corrosion of Z3CN20.09M cast austenite stainless steel (CASS) which is widely used in the primary coolant pipes of nuclear power plants was investigated by potentiodynamic anodic polarization and electrochemical impedance spectroscopy (EIS). The results show that the pitting potential and charge transfer resistance of the steel decrease with the increase of thermal aging time. It is interesting to note that the pitting potential and charge transfer resistance of specimens aged first and then annealed at 550℃ for 1 h increase up to those of the unaged. The results confirm that Cr-rich α' phase is dissolved in ferrite after annealing, but G phase still exists in ferrite at the same time, indicating that α' phase precipitated in ferrite is the main reason for the deterioration in pitting corrosion resistance of the thermally aged Z3CN20.09M steel.
Abstract: The heredity of primary Fe2B in the solidification structure of hypereutectic Fe-C-B alloys and a uniform treatment method were investigated by remelting and electric pulse treatment. The results show that it is difficult to eliminate the heredity of primary Fe2B only by remelting. When exerting electric pulse at a lower remelting temperature, it changes the distribution of primary Fe2B in the solidification structure but does not change the long rod shape. But when exerting electric pulse at a higher remelting temperature, it can eliminate the effect of solidification structure heredity, the shape of Fe2B changes from the long rod shape to particle shape, and the precipitation of Fe2B decreases obviously.
The surface morphology of an aviation organic coating during indoor accelerated testing was continually observed by a prestrain method. Environmental scanning electron microscopy and electrochemical impedance spectroscopy were employed for micro-structural characterization and characteristic impedance modulus analysis to systematically study the degradation behavior and failure model of the organic coating under the co-effect of prestrain and tropical marine atmosphere. It is found that the protective properties of the organic coating show a dramatic decrease after tensile prestrain application and go further down during indoor accelerated testing;the degradation of the organic coating is positively correlated with the tensile prestrain level. It is thought that the loss of the protective properties is due to the relatively high stress level which exceeds the breaking strength of the organic coating materials, leading to the formation of microcracks, which serve as routes to the organic coating/alloy interface for solution. But the protective properties of the organic coating exhibit no change after compressive prestrain application and decrease slowly during indoor accelerated testing;the degradation of the organic coating is negatively correlated with the compressive prestrain level.
Abstract: The characteristics of a supersonic oxygen jet at different environmental temperatures were studied by numerical simulation and compared with previous experimental results. It is found that the velocity attenuation of the oxygen jet is inhibited and the jet core length is extended under a high temperature environment compared with a low temperature environment. The jet temperature at different environmental temperatures becomes higher with oxygen diffusion and is close to environmental temperature finally. The jet pressure distribution has the same trend with the jet velocity distribution. The numerical simulation results of jet velocity, temperature and pressure have a relative high correlation with the measured values.
Abstract: The disadvantages of the analytical solution and the simplified method were analyzed and a thermal expansion model was established by the finite element method. Based on the data characteristics of the rolls' geometry in a rolling unit, the calculation task was divided into pre-calculation responsible for static data preparation and renewal calculation responsible for renewing dynamic data and thermal expansion. The pre-calculation was called only after roll change and the renewal calculation was called when the thermal expansion data was needed to be updated. This special tailored flow contributes to a much smaller computation complexity in comparison with standard finite element analysis. Furthermore, the corresponding program was compiled according to the tailored flow and its results are in agreement with those by ANSYS, with the accuracy of about 30% higher than the simplified method. Due to high accuracy and short calculation time, this home-made finite element analysis program is promising to be implemented in online applications for evaluating the thermal expansion of rolls.
Abstract: A kind of four-dimensional (4D) four-wing chaotic system was proposed based on the odd function. The chaotic system can generate four wings on a certain plane by adjusting some parameters. Its basic dynamic behaviors including equilibria, dissipativity and Lyapunov exponents were analyzed by numerical simulation. The sensitivity of system parameters to the chaotic behavior was also studied. When the parameters vary, the phase diagram can present periodic orbits, chaos, and other states. An oscillation circuit was designed for the chaotic system, and MUTISIM observed results have a good consistency with numerical simulation.
Abstract: Based on Mahalanobis distance and the fuzzy C-means algorithm, this article introduces a digital color image matting algorithm. First the red, green and blue color components of color image pixels are normalized. Second the appropriate mask as a sample set is selected in the background of the normalized image, and the Mahalanobis distance between each pixel and the sample set is calculated. Third the calculated Mahalanobis distances are classified into two categories using the fuzzy C-means clustering algorithm:the foreground and the background. Finally, the quality of the matting is improved using the filling-hole technique. Eight images have been processed for comparison, the results show that this algorithm can automatically segment these images, and is better than the Mahalanobis distance algorithm, fuzzy C-means clustering algorithm and linear regression algorithm.
Abstract: In order to decide the appropriateness of a new user applying to join in a group in the social network, a privacy-preserving protocol was designed by the secure sum protocol and secure comparison protocol. In the privacy-preserving protocol, the secure basis protocol was devised for problems under a one-dimensional linear model, and the advanced protocol for a multi-dimensional model with a circular boundary. For the case of a single applicant and a multi-user group, the solution was converted and realized in a two-party computation model. After the proof of correctness, the complexity was discussed, and there is no leaking message during the process by the analysis of data views in each step. The privacy-preserving protocol avoids not only the blindness of auto recommendation by the net-system but also the decision delay due to the administrator's offline. In the meanwhile, the privacy of the applicant and group members can be protected without leaking any information.
Abstract: An exact motion equation for core-wall suspension structure systems was establish by using the Lagrange equation. Considering the effect of large displacement with nonlinearity, the seismic dynamic response time history of the system was solved by the Runge-Kutta method. Calculation results show that the system can significantly decrease the inter-storey drift, velocity and acceleration, and the seismic mitigation efficiency is approximately 90%. Sectional bending stiffness has the most significant influence on the sectional force and translational deflection, and the sectional force increases with increasing sectional bending stiffness. However, suspender length and the damp coefficient of storey dampers have little influence on the sectional force. The damp coefficient has optimum values to the inter-storey drift and sectional force. The storey drift, velocity and acceleration exhibit monotonous decrease with the damp coefficient.
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
