电机加载测试系统中变频器的高-低-高应用研究

各类型电机在使用过程中不可避免地要进行检修维护,当检修完成后,要判断并确认其是否达到相应维修标准,是否满足相关使用要求,进行电机的加载测试是主要的途径之一。采用变频器对拖的测试方式是目前主流的电机加载测试方案,但直接采用该方式进行电机测试电源系统的设计往往无法满足所有的现场测试要求。本文就神东煤炭有限责任公司煤矿用设备电机的加载测试需求,在变频器对拖测试的基础上对测试电源系统进行了一系列的优化设计,采用变压器实现变频器的高-低-高应用来解决作业现场的遇到的问题,实现了更加高效节能的电机加载测试。

高压变频技术在韶关冶炼厂的应用

介绍了高压变频器采用的几种结构形式,具体分析了在韶关冶炼厂应用的情况,并对在实际应用中所遇到的一些问题提出了解决的方法。不仅满足了生产工艺对风机调速特性的要求,而且方便了生产操作,节约了大量的电能。

Wall Sticking of High Water-Cut, Highly Viscous and High Gel-Point Crude Oil Transported at Low Temperatures

Some crude oils with high water cut have the capability to flow below the oil gel point, while the oil particles adhere to the pipe wall in the form of paste, also called "wall sticking". Wall sticking is a serious problem during the pipeline transportation, leading to partial or total blockage of the pipeline and energy wastage. In this paper, a series of laboratory flow loop experiments were conducted to observe the wall sticking characteristics of crude oil with high water cut, high viscosity and high gel point at low transportation temperatures. The effects of shear stress and water cut on the wall sticking rate and occurrence temperature were investigated. Experimental results indicated that the wall sticking rate and occurrence temperature were lower under stronger shear stress and higher water cut conditions. A criterion of wall sticking occurrence temperature(WSOT) and a regression model of wall sticking rate were then established. Finally, the software was developed to calculate the pressure drop along the pipelines of crude oils with high water-cut. It was able to predict the wall sticking thickness of gelled oil and then calculate the pressure drop along the pipelines. A typical case study indicated that the prediction results obtained from the software were in agreement with actual measured values.

Development of Light Cycle Oil(LCO) Hydrocracking Technology over a Commercial W-Ni Based Catalyst

Because of its high density and low cetane number, the light cycle oil(LCO) containing heavy aromatics(60%—80%) can hardly be transformed through the conventional hydro-upgrading technology. In this report, a novel LCO hydrocracking technology(FD2G) was proposed for the utilization of LCO to manufacture high value-added products. Through the ingenious combination of hydroprocessing catalyst and the hydrocracking process, the high octane gasoline and the ultra-low sulfur diesel(ULSD) blendstocks were produced simultaneously. The influence of catalyst type, reaction temperature, pressure, respectively, on the research octane number(RON) of produced gasoline was studied in a fixed bed hydrogenation reactor. It indicated that high reaction temperature and medium pressure would favor the production of highoctane gasoline through the conversion of bi-aromatic and tri-aromatic hydrocarbons. The typical results of FD2 G technology on commercial units showed that it could produce clean diesel with a sulfur content of less than 10 μg/g and clean gasoline with a research octane number(RON) of up to 92. It would be contributed to the achievement of the maximum profit of a refinery, the FD2 G technology could provide a higher economic efficiency than the other diesel quality upgrading technology under the current gasoline and diesel price system.

矿井风机变频调速控制系统的改造

通过采用Siemens S7-300PLC控制器和Danfoss VLT5252变频器对通风机控制系统进行改造,利用变频调速来改变风量大小,再综合原有煤矿风机控制系统的结构和特点等各个方面的因素,最终采用"高-低-高"的变频控制方案。

High-temperature treatment induced carbon anode with ultrahigh Na storage capacity at low-voltage plateau

Sodium-ion batteries （NIBs） show great prospect on the energy storage applications benefiting from thei low cost and the abundant Na resources despite the expected lower energy density compared wit lithium-ion batteries （LIBs）. To further enhance the competitive advantage, especially in energy densit3 developing the high-capacity carbon anode materials can be one of the effective approaches to realiz this goal. Herein, we report a novel carbon anode made from charcoal with a high capacity of ~400 Ah g i, wherein about 85% （〉330 mAh g^-1） of its total capacity is derived from the long plateau regio below ~0.1 V. which differs fiom those of typical hard carbon materials （~300 mAh g^-l） in NIBs but i similar to the graphite anode in LIBs. When coupled with air-stable Nao.gCuo.22Feo.3oMno.4802 oxid cathode, a high-energy density of ~240 Wh kg^-1 is achieved with good rate capability and cyclin stability. The discovery of this promising carbon anode is expected to further improve the energy densit of NIBs towards large-scale electrical energy storage.

Vertical structure of longitudinal differences in electron densities at mid-latitudes

By using Constellation Observing System for Meteorology, Ionosphere, and Climate satellite observa- tions, and Global Ionosphere and Thermosphere Model simulations, the altitudinal dependences of the longitudinal differences in electron densities Ne were studied at mid- latitudes for the first time. Distinct altitudinal dependences were revealed： （1） In the northern （southern） hemisphere, there were wave-1 variations mainly in the daytime in the altitudes below 180 km, but wave-2 （wave-l） variations over a whole day above 220 km; （2） a transition （or sep- aration） layer occurred mainly in the daytime within 180 and 220 km, showing reversed longitudinal variation from that at lower altitudes. Solar illumination was one of the plausible mechanisms for the zonal difference of Ne at lower altitudes. At higher altitudes, both neutral winds and solar illumination played important roles. The neutral winds effects accounted for the longitudinal differences in Ne in the European-Asian sector. Neutral composition changes and neutral wind effects both contributed to the formation of the transition layer.

Fabrication of Large Area High Density, Ultra-Low Reflection Silicon Nanowire Arrays for Efficient Solar Cell Applications

High density vertically aligned and high aspect ratio silicon nanowire （SiNW） arrays have been fabricated on a Si substrate using a template and a catalytic etching process. The template was formed from polystyrene （PS） nanospheres with diameter 30-50 nm and density 10^10/cm^2, produced by nanophase separation of PS-containing block-copolymers. The length of the SiNWs was controlled by varying the etching time with an etching rate of 12.5 nm/s. The SiNWs have a biomimetic structure with a high aspect ratio （-100）, high density, and exhibit ultra-low reflectance. An ultra-low reflectance of approximately 0.1% was achieved for SiNWs longer than 750 nm. Well-aligned SiNW/poly（3,4-ethylenedioxy-thiophene）：poly（styrenesulfonate） （PEDOT：PSS） heterojunction solar cells were fabricated. The n-type silicon nanowire surfaces adhered to PEDOT：PSS to form a core-sheath heterojunction structure through a simple and efficient solution process. The large surface area of the SiNWs ensured efficient collection of photogenerated carriers. Compared to planar cells without the nanowire structure, the SiNW/PEDOT：PSS heterojunction solar cell exhibited an increase in short-circuit current density from 2.35 mA/cm^2 to 21.1 mA/cm^2 and improvement in power conversion efficiency from 0.4% to 5.7%.

Subtransus deformation mechanisms of TC11 titanium alloy with lamellar structure

Isothermal compression tests are applied to study the deformation mechanisms of TCll titanium alloy with lamellar structure under the deformation temperature range of 890-995 ℃ and strain rate range of 0.01-10 s^-1. According to the flow stress data obtained by compression tests, the deformation activations are calculated based on kinetics analysis of high temperature deformation, which are then used for deformation mechanism analysis combined with microstructure investigation. The results show that deformation mechanisms vary with deformation conditions： at low strain rate range, the deformation mechanism is mainly dislocation slip; at low temperature and high strain rate range, twinning is the main mechanism; at high temperature and high strain rate range, the deformation is mainly controlled by diffusion offl phase.

A necklace of pearl in high altitude medicine and hypoxic physiology in Yushu Earthquake

During Yushu Earthquake,a large number of rescuers flocked to the mountainous quake areas. Under such a very specific circumstance,a high incidence of acute altitude illness was observed in rescuers who rapidly traveled from near sea level to an altitude of 4 000 m. It is evident that acute altitude illness leads to a significant human and economic toll,and also seriously influences the mountain rescue operation. So what does this teach us about mountain rescue in Yushu? Professor Wu Tianyi and many other authors collected shining points of the experiences and drew the lessons from the Yushu Earthquake into this special issue in Engineering Sciences which is like to thread pearl beads for a necklace. What readers learn from this special issue will have implications for the health and well-being of all high altitude populations all over the world.

Third generation high strength low alloy steels with improved toughness

On-line thermo mechanical controlled processing(TMCP) was conducted to develop the third generation high strength low alloy(HSLA) steel with high toughness economically.The ultra-low carbon content ensured a high level of upper shelf energy while ultrafine lath martensitic structure transformed from super-thin pancaked austenite during controlled rolling and cooling.The reduction of martensite block size decreased ductile-to-brittle transition temperature(DBTT) and compensated the strength loss due to carbon reduction.Consequently,the excellent balance of strength and toughness values was obtained as 950-1060 MPa for yield strength,180 J for Charpy V-notch impact absorbed energy at 30℃,which is much superior to that of traditional martensitic steel.Two mechanisms for the refinement of lath martensite block were proposed:One is the austenite grain refinement in the direction of thickness,and the other is the reduction in the fraction of sub-block boundaries with small misorientation and the increase in the fraction of block boundaries with large misorientation,possibly due to austenite hardening.

High performance steels:Initiative and practice

In order to meet the progressive requirement for the performance improvement of steel,the author proposed a novel microstructure featured with multi-phase,meta-stable and multi-scale(so-called as M 3).And then,the new technologies could be developed to process three prototype steels with high performance:the third generation high strength low alloy(HSLA) steels with improved toughness and/or ductility(AKV(40℃)≥200 J and/or A≥20% when Rp0.2 in 800-1000 MPa),the third generation advanced high strength steels(AHSS)(Rm×A≥30 GPa% when Rm from 1000 MPa to 1500 MPa) for automobiles with improved ductility and low cost,and heat resistant martensitic steels with improved creep strength(10000650≥90 MPa).It can be expected that the new technology developed will remarkably improve the safety and reliability of steel products in service for infrastructures,automobiles and fossil power station in the future.

Prediction of Hub Corner Stall Characteristics of a Highly Loaded Low Speed Single Stage Fan

In this paper a numerical investigation has been presented on the stall mechanism of a highly loaded Single Stage Low Speed Fan designed for the research test facility to be installed at North Western Polytechnic University (NWPU) Xi’an, China. The results presented are for the design point, near stall and just stall operating conditions at design speed. Design point studies have been found to be an indicative of stall area. Unsteady method of domain scaling has been used to compute the results at near stall and just stall conditions. It has been found that unlike the conventional tip leakage flow of the rotor, stator hub section is mainly responsible for the stall of the fan. The flow mechanism has been discussed with correlation to the design variables and previous investigations. Commercial CFD code NUMECA FINE/Turbo has been used for computations; results have been compared with results obtained from commercial CFD code ANSYS-CFX. The loss prediction of latter code is conservative than the former. The stall mechanism predicted by both codes is analogous.

CO_2 permeability of fractured coal subject to confining pressures and elevated temperature: Experiments and modeling

The CO_2 permeability of fractured coal is of great significance to both coalbed gas extraction and CO_2 storage in coal seams, but the effects of high confining pressure, high injection pressure and elevated temperature on the CO_2 permeability of fractured coal with different fracture extents have not been investigated thoroughly. In this paper, the CO_2 permeability of fractured coals sampled from a Pingdingshan coal mine in China and artificially fractured to a certain extent is investigated through undrained triaxial tests. The CO_2 permeability is measured under the confining pressure with a range of 10–25 MPa, injection pressure with a range of 6–12 MPa and elevated temperature with a range of 25–70°C. A mechanistic model is then proposed to characterize the CO_2 permeability of the fractured coals. The effects of thermal expansion, temperature-induced reduction of adsorption capacity, and thermal micro-cracking on the CO_2 permeability are explored. The test results show that the CO_2 permeability of naturally fractured coal saliently increases with increasing injection pressure. The increase of confining pressure reduces the permeability of both naturally fractured coal and secondarily fractured coal. It is also observed that initial fracturing by external loads can enhance the permeability, but further fracturing reduces the permeability. The CO_2 permeability decreases with the elevation of temperature if the temperature is lower than 44°C, but the permeability increases with temperature once the temperature is beyond 44°C. The mechanistic model well describes these compaction mechanisms induced by confining pressure, injection pressure and the complex effects induced by elevated temperature.