冷却速率对钢中MnS+Al_2O_3复合夹杂物包裹率的影响研究

通过实验室试验研究钢中MnS+Al_2O_3复合夹杂物的生成以及不同冷却速率对MnS+Al_2O_3复合夹杂物包裹率的影响。结果表明:被推动到钢液凝固前沿的Al_2O_3,会为MnS析出提供异质形核质点;随着冷却速率的增加,复合夹杂物的尺寸从4μm降至2.5μm左右,MnS+Al_2O_3复合夹杂物包裹率逐渐降低。本次试验研究为得到较优包裹程度的实验条件以及进一步改善钢材性能提供一定的理论分析。     

电解提取风电齿轮钢夹杂物研究

采用小样电解法对风电齿轮钢18CrNiMo7-6中的夹杂物进行了系统的分析检测,通过对齿轮钢中夹杂物的电解、提取、分离,较为完整地将钢中的夹杂物电解并收集,借助SEM-EDS对所收集的夹杂物进行了定性分析。结果表明:通过小样电解法可以较为完整地得到风电齿轮钢18CrNiMo7-6中夹杂物的三维形貌;Al2O3、Al2O3-SiO2类夹杂物多呈不规则多边形状,平均尺寸分别为29.7μm、15.81μm,A l2O3-MgO-CaO-SiO2复合类夹杂物通常为包裹形态的球状,平均尺寸为13.1μm,Ca O类夹杂物通常呈块状,平均尺寸为11.7μm,MnS类夹杂物形貌多呈长条状或纺锤状,平均尺寸为18.8μm,Ca S类夹杂物通常呈规则长条状,平均尺寸为9.2μm;与传统金相法相比,小样电解法在观察钢中夹杂物真实的三维形貌和尺寸时是更为行之有效的方法。     

稀土耐热钢凝固过程中夹杂物析出的热力学分析

基于FactSage热力学软件的最小吉布斯自由能原理,系统研究了不同铈含量及钢液洁净度条件下耐热钢凝固过程中夹杂物的析出行为。结果表明：耐热钢中添加铈后,高熔点的Ce2O2S、 Ce2O3等夹杂取代了SiO2与MnS夹杂;在一定洁净度条件下, SiO2与MnS无法析出的铈含量分别为0.02%与0.03%;随着氧含量的增加,耐热钢中的夹杂物类型由Ce2O2S、 CeN、 CeS向SiO2、 Ce2O3转变,当氧含量大于0.006%时,钢中开始析出SiO2夹杂;随着硫含量的增加,耐热钢中的夹杂物类型由Ce2O2S、 CeN、 CeS、 Ce2O3向Ce2O2S、 MnS、 Ce2S3转变,当硫含量大于0.005%时, MnS夹杂开始析出。     

60Si_2Mn-Cr弹簧钢中夹杂物演变行为分析

针对某钢厂60Si_2Mn-Cr弹簧钢的生产工艺,取不同工位处的钢样,研究夹杂物的转变效果。实验表明:微铝工艺生产钢中的夹杂物逐渐转变为Al_2O_3-SiO_2-CaO-MgO复合氧化物夹杂,形状逐渐趋于球状夹杂物尺寸逐渐减小,最终铸坯中夹杂物的平均尺寸为4.6μm。通过热力学计算,得到了不同工位下夹杂物的SiO_2+CaO-MgO-MnO+Al_2O_3相图,在中间包和铸坯中的夹杂物大多数处于1500-1 600℃温度下的液相区,减小高硬度夹杂物的危害,提高了弹簧钢的质量。     

矩形单元蓄热特性及结构优化CSCD

利用FLUENT软件对矩形单元内石蜡的熔化过程进行了数值模拟,分别研究不同的矩形单元上部尺寸、不同壁面温度对单元内石蜡熔化过程的影响,通过非线性拟合获得了单元内液相分数β与无量纲数Fo、Ste、Ra的准则关系式,为优化矩形单元内PCM总体熔化速率提供了方案与依据。研究结果表明:在石蜡熔化过程中,自然对流作为主导传热方式的时间比例随矩形单元上部尺寸的增加先增大后减小;自然对流对传热的强化作用随矩形单元内上部尺寸增加而增大,但平均储热速率随单元内上部尺寸的增加先增大后减小直至趋于平稳,存在最优值;温差是影响PCM熔化的关键因素之一,将温差从43℃提高至53℃,再从53℃提高至63℃熔化时间分别缩短14.63%、24.26%不等。     

高氮钢电渣重熔夹杂物控制研究

对高氮钢电渣重熔前后夹杂物进行对比研究,分析不同渣系和自耗电极氧含量对重熔后夹杂物的影响。研究发现,不同渣系对电渣钢的洁净度影响很大,适当提高w(Ca O)/w(Al2O3)可有效降低电渣锭中的夹杂物和全氧量。对高氮钢电渣重熔的脱硫进行研究,分析了不同渣系和熔炼速率对高氮钢脱硫率的影响,实验结果表明:电渣重熔后,硫化物夹杂的平均直径和单位面积数量大大减少,夹杂物的主要类型为Mn S+Al2O3复合型夹杂物,同时适度提高渣中Ca O含量实现提高硫分配比是提高脱硫效率的有效手段。脱硫动力学推导中发现重熔速率越低,脱硫效果越明显,但实验发现脱硫率随重熔速率的降低呈现先降低后升高的趋势,其原因在于渣池中发生硫化物富集,导致"回硫"现象发生。     

50CrVA弹簧钢夹杂物特性研究

采用全流程多级取样的方法,对国内某钢厂BOF-LF-CC工艺生产的50CrVA弹簧钢中夹杂物特性的演变规律进行系统分析和研究。实验结果表明:随着精炼和连铸过程的进行,钢中的夹杂物种类逐渐由SiO2-Al2O3-MnO-TiO2夹杂物转变为CaO-Al2O3-MgO和CaO-A l2O3-SiO2夹杂物。最终铸坯夹杂物中的Al2O3组元含量约为70%～75%,而Ca O含量仅为5%～10%。夹杂物熔点较高,改性不充分。建议在生产中,强化钙处理或提高炉渣碱度来实现夹杂物的低熔点化,降低其危害。     

EAF-RH-LF-CC生产Q345B的洁净度研究

在炼钢过程各工位取样,分析研究了EAF-RH-LF-CC工艺下Q345B无缝管钢的洁净度.试验结果表明：（1）铸坯中的总氧含量可以稳定在0.002%左右;（2）非金属夹杂物以近似球形的氧化物和硫化物居多,其数量依炼钢流程工序不断降低,且精炼过程中降幅最大.（3）LF过程有明显的增氮现象,需控制LF过程的二次氧化;（4）与RH过程相比,在LF结束时钢中10～20μm的夹杂数量较多,应适当延长LF脱氧后的软吹时间;（5）RH精炼初渣中w（FeO＋MnO）过高,RH钢包渣需进行改质处理.     

Ca处理对55SiMnMo夹杂物行为变化的研究

研究了Consteel电弧炉-LF-VD-连铸工艺生产55SiMnMo时钙处理对钢中夹杂物行为变化的影响,对显微夹杂物、夹杂物成分变化及大型夹杂物进行分析。结果表明,喂钙线后2 min时钙处理并未反应完全,VD结束后夹杂物钙处理变性效果明显且钙主要与夹杂物表面反应。对Mg-Al-Ca类夹杂物成分分析得出,钙线的加入使钢中夹杂物Ca含量明显增加,(Al2O3)由VD入位80%～90%降低至中间包中的40%～60%,(Mg)最终降低至10%以下。钙处理对大型夹杂物影响较小。     

方坯连铸机内不同形貌夹杂物的去除行为

采用数值模拟方法研究小方坯连铸结晶器的三维流场和夹杂物运动轨迹,探讨了粒子形状对夹杂物去除率的影响.结果表明:相同形状夹杂物,随着粒径的增大,夹杂物的去除率随之增大;相同粒径的夹杂物,形状因子越小的夹杂物的去除率越高;对于5 μm以下尺寸的夹杂物,夹杂物的形状和尺寸对夹杂物运动行为的影响可以忽略.     

Contents in Volume 23,2014

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Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法,这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。