工艺参数对低温液体喷射混合器混合性能的影响

为了优化液化天然气气质,探究工艺参数对低温液体喷射混合器内部流场的影响,基于不同沸点低温液体互溶混合机理,以液态甲烷、液态丙烷为工质,分析了不同工艺参数喷射混合器内两股流体的流动特性和混合效果。分析结果表明:喷射混合器的主流体入口压力、引射流体入口压力及混合流体出口压力均存在一个最优值,在考虑实际生产环境的基础上,应使其值尽可能的接近这一临界值;在其他工艺参数确定的情况下,随着引射流体入口温度的增大,喷射混合器的混合性能越好,可适当增大引射流体入口温度,以提高喷射混合器的混合性能。主流体入口压力0.22 MPa、引射流体入口压力0.1 MPa、混合流体出口压力0.1 MPa、引射流体入口温度249.15 K时,该结构喷射混合器的混合性能最好。     

压力型雾化喷嘴射流喷雾气-液两相流数值模拟

为了研究喷雾压力和环境气流速度对射流喷雾的雾化效果及喷雾雾场的均匀性的影响,基于流体力学理论,建立压力型喷嘴喷雾的数值计算模型,利用计算流体动力学软件Fluent对喷雾雾场进行气-液两相流数值模拟研究,并通过大量的数据统计定量分析雾滴粒径的分布情况。结果表明:在喷射压力一定时,风速越大雾滴飘移能力越强,风速过大或过小都将严重影响雾化雾场的均匀性;在一定范围内喷射压力越大,雾化效果越好,所形成的雾滴平均粒径越小。     

喷嘴结构对真空喷射雾化性能影响研究

基于Fluent软件模拟了柱型、扇型、锥型和混合型喷嘴真空喷射射流雾化过程,研究了喷嘴结构对动压力转换、射流速度和喷嘴出口湍动能的影响。结果表明,锥型喷嘴动压力较大,可提高静压能转换效率;扇型和锥型喷嘴喷射束宽度较大,利于大面积喷射成膜;扇型喷嘴易形成空化,出口湍动能较大,有助于液滴初次雾化破碎,而混合型喷嘴的空化层厚度最小,湍流区域最大。通过分析雾化锥角与喷嘴流量系数,发现扇形和锥直形喷嘴具有较大雾化锥角,但流量系数较小喷嘴压力损失较大;喷嘴直线段会提高锥型喷嘴雾化锥角和喷嘴出口湍动能,并使扇型喷嘴的流量系数增大,但射流雾化锥角减小。最后,本文尝试构建了真空喷射射流雾化数学模型。     

EHD喷印技术相关参数数值分析

目的对基于电-液耦合动力学原理(简称EHD)喷印技术的相关参数,进行锥射流和滴落模式下的数值分析研究。方法在锥射流模式中,对毛细凝结加热液体喷射的物理模型进行调整,以适用于EHD喷印;对滴落模式的液滴沉积过程,引入表面张力概念进行数值分析。运用数值法得到了锥射流的轮廓图,集中讨论了流量和净高度对射流直径的影响;重点研究了液滴直径与电压频率和液体表面张力之间的关系,并将理论结果与实验和经验数据进行了比较分析。结果锥射流模式在一定条件下,射流直径随着流量和净高度的增大而增加;在滴落模式中,得到的液滴直径随电压频率和流体表面张力的增大而减小,且数值分析得到的结果与实验结果相一致。结论对相关参数进行数值分析是对实验研究的补充,为EHD喷印技术研究提供了理论参考。     

平口喷嘴的真空射流雾化模拟分析

基于breakup和collsin液滴破碎模型采用Fluent和Gambit软件对平口喷嘴的真空射流雾化进行了模拟,研究了环境压力、喷射压力和喷嘴直径等参数对射流雾化结构和液滴索特平均直径(Sauter mean diameter,SMD)的影响.结果表明:①随着环境压力的降低,喷射束宽度减小,射流贯穿距离和SMD增加.当环境压力小于0.01 MPa时,各雾化性能参数的变化幅度减小;②环境压力和喷嘴直径一定,随着喷射压力的增加,喷射束宽度呈先快速后缓慢增加的趋势,而射流贯穿距离近似线性增加,SMD值变化不明显;③喷嘴直径越小,喷射束宽度和射流贯穿距离越大,SMD值越小,射流雾化效果越好,更易制备出光滑致密的聚合物薄膜.     

低压环境下喷雾特征实验研究北大核心CSCD

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

双锥药型罩结构参数对聚能射流的影响

为探究双锥药型罩结构参数对聚能射流速度的影响,采用数值仿真模拟双锥型药型罩形成射流的过程。结果表明:双锥药型罩较单锥结构形成的有效射流更加密集,且形成射流的头部最大速度及射流平均速度均大于单锥药型罩。通过因素影响分析结果可知,大、小锥罩角度的变化对射流头部速度影响均显著,且大、小锥罩角度差距越大,形成射流的平均速度越大,同时还能保持较高的射流头部速度。双锥罩罩顶距壳体起爆点距离越小,形成的射流头部最大速度越大,且侵彻深度越深;距起爆点越远,形成射流的平均速度越大,侵彻扩孔能力越强。     

低压环境下喷雾特征实验研究

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

几何结构参数对喷射器性能影响实验研究

在自行搭建的喷射器性能测试实验台上,以CO_2、N_2及R290为工质,通过改变喷射器喷嘴临界截面直径,总结喷射器喷射系数在不同的引射流体入口压力、工作流体入口压力及工质种类条件下的变化规律。实验设定工作流体温度为90℃,喷射器背压为3. 9 MPa,工作流体入口压力变化范围为8. 0—10. 0 MPa,引射流体入口压力变化范围为2. 4—2. 9 MPa,喷嘴临界截面直径变化范围为0. 68—0. 72 mm。实验结果表明:当保持喷射器的基本工作参数不变,引射流体入口压力为一定值时,喷射器喷射系数随喷嘴临界截面直径的减小而逐渐增大;当保持喷射器的基本工作参数不变,工作流体入口压力为一定值时,喷射器喷射系数随喷嘴临界截面直径的增大而逐渐减小;在相同工作压力下,喷射系数大小依次是N_2、CO_2、R290;在相同引射压力下,N_2、CO_2先达到稳定状态;在保持喷射器的基本工作参数不变时,工作流体入口压力及引射流体入口压力的提高对喷射器喷射系数均有提升作用。     

高背压下平口喷嘴射流锥角影响因素分析

高背压下条件下的射流在火电的减温水喷射、燃气轮机、加压煤气化、潜艇等领域具有广泛的应用。由于高背压射流参数计算方法缺失,本文利用搭建的高背压实验系统,选取8种不同结构参数的喷嘴进行实验,研究背压、喷射压差、喷嘴长径比等参数对射流锥角的影响。分析实验结果,发现背压对射流锥角影响较大,在高背压时,背压越高,射流锥角越大;在低背压时,射流锥角受喷嘴内部流动状态影响较大,低背压时,喷嘴内部易产生空穴流动,空穴的产生促进射流锥角的增大,其影响不可忽略。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.