真空高压气淬炉中淬火气体压力、流速和类型对工件冷却性能影响的数值模拟

本文运用FLUENT软件,通过大量的计算机模拟,研究了真空高压气淬炉中淬火气体压力、进口速度、气体类型对工件冷却性能的影响.通过对比氮气在0.45 MPa、0.6 MPa、1.0 MPa和1.5 MPa淬火压力下工件的冷却速度,量化了淬火压力对工件冷却速度的影响程度.氮气在0.6 MPa下,将气体速度由40 m/s增至60m/s,工件冷却速度提高27％,但风机功率增加3.4倍.由于气体体积流量一定的情况下,淬火气体比热和密度的协同影响了换热系数的大小,通过计算机模拟了四种淬火气体氢气、氦气、氮气和氩气对工件冷却速度的影响,得出在相同气体压力和流量下,四种气体的冷却能力是:氮气＞氢气＞氦气＞氩气;在消耗相同的风机功率下,密度小比热大的气体冷却能力高,四种气体的冷却能力依次是氢气＞氦气＞氮气＞氩气.     

链条炉内气流场试验研究与模拟

对链条锅炉炉内增拱进行了理论分析,然后采用飘带与风速仪测量相结合的方法对炉内增加前拱后的不同负荷下空气动力场进行了冷态试验研究,同时通过CFD进行了数值模拟验证,给出了不同负荷下速度流场分布图,为锅炉技术改造提供理论和试验依据。     

冷却风扇离心叶轮及蜗壳中流场的显示技术

目前对改进和提高军用冷却风扇的性能日趋强烈,提高冷却风扇性能的最大前景在于期望有一个很大程度上对真实流动现象的了解,流场显示是搞清流动现象的必不可少的技术.流动显示技术通常分为两大类,最常用的有丝线法、示踪粒子法、染色法、烟气法等.随着计算机技术的发展,应用计算机仿真技术能较快的对已设计的冷却风扇进行流场模拟计算,实现优化设计,是冷却风扇现代设计的方向.     

稀薄气体流动的粒子图像测速实验研究

建立了一套可对真空度进行调节的实验装置,从大气压开始逐渐降低系统压力,进行系列稀薄气体流动的PIV流场实验.系统压力从101kPa、90kPa逐次降至10kPa,使用所选粒子在不同系统压力下分别进行PIV实验获得测量区域流场分布情况.运用计算流体力学的方法模拟大气压条件下实验区域的内部流动,对比结果发现该种条件下数值模...     

低温阀门冷态试验的动态传热过程模拟与分析

在确定不锈钢在液氮中沸腾换热系数的基础上,结合其在低温下的物性参数,利用有限元分析软件ANSYS对一低温阀门在正常运行和冷态试验状态下的温度场进行模拟与分析。针对冷态试验情况下填料函处出现冻结的问题,提出在阀杆处添加绝热层的方案,继而通过进一步的模拟计算预测了其改进效果。     

第十四讲:真空工程用焊接技术

（上接2006年第6期第63页）热态真空度又称工作真空度，是指从开始加热到充气冷却这段时间的炉内真空度，这是由于加热时，零件、夹具要析出气体；使用膏状钎料时粘结剂要挥发。这些因素都会不同程度地引起冷态真空度的降低。但是在钎焊温度下，要求炉内真空度基本恢复到冷态真空度，通常是采用适当延长稳定时间的方法来实现的。如果钎料中含有蒸气压较高的合金元素，为了防止合金元素大量挥发而污染炉膛，这时热态真空度与冷态真空度相差较大。例如用铜基钎料时，因为铜在940℃时的蒸气压为1Pa，     

机械通风直接空冷系统噪声预测与分析

直接空冷系统采用大型轴流风机群对汽轮机排汽进行冷却,因此直冷系统噪声成为电站主要考虑的问题之一。该文利用计算流体软件Fluent对直接空冷单元和5×6规模的空冷岛进行流场模拟和噪声预估,并模拟增加消音墙后的空冷岛流场和噪声的变化情况。流场模拟的紊流模型采用大涡模拟（large eddy simulation,LES）,噪声预估采用非稳态隐式求解。结果表明,在挡风墙内侧布置多孔吸声材料对空冷岛流场基本没有影响,但是它可以有效降低整个空冷岛的噪声水平,主要是降低了低频率的噪声。     

硅单晶Czochralski法生长全局数值模拟Ⅰ.传热与流动特性

利用有限元方法对炉内的动量和热量传递过程进行了全局数值模拟,研究了硅单晶Czochral-ski(Cz)法生长时的总体传热和流动特性.假定熔体和气相中的流动都为准稳态轴对称层流,熔体为不可压缩流体,Cz炉外壁温度维持恒定,模拟结果表明:熔体流型及炉内传热特性与Marangoni效应密切相关,设置在晶体和坩埚间的气体导板能降低加热器的功率并改变熔体流型.     

H3636真空正压气淬炉的冷却性能研究

通过在Ｈ３６３炉中测试冷却过程曲线,研究气体在真空炉内热变换规律,并比较不同压力及空冷,油冷冷却速度,掌握了Ｈ３６３６炉冷却能力与压力的关系,对今后生产,研究起到指导作用。     

盘型分子泵3D过渡流特性

采用直接模拟蒙特卡罗方法对过渡流态下盘型分子泵的抽气特性进行了模拟研究,并讨论了盘型分子泵通道几何参数对流动特性的影响.指出了通过改变泵的尺寸参数提高抽气系数的途径.最后,进行了实验研究和模拟研究结果的对比,证明模拟计算结果在允许的误差范围内.     

灯泡贯流式水轮发电机通风系统流场的数值模拟

以计算流体力学(CFD)软件FLUENT为工具,对灯泡贯流式水轮发电机通风系统的流场进行数值模拟。建立了灯泡贯流式水轮发电机通风系统的三维几何通风模型,用标准κ-ε湍流模型作为气流的物理模型,并对计算出的电机空气风量分配情况与实测数据进行比较,验证了数值模拟的可靠性。研究表明,在合理的简化条件下,采用CFD能准确地模拟灯泡贯流式水轮发电机的通风系统流场,为进行灯泡贯流式水轮发电机通风系统设计和优化提供有效的依据。     

污染气体红外光谱仿真及参数设置研究

利用红外辐射传输理论,阐述了污染气体红外光谱仿真的基本模型,提出了在已知背景光谱和干扰物光谱的情况下进行污染气体红外光谱仿真的方法。仿真结果与实测光谱进行了验证比较,说明了仿真方法的可行性。研究了大气温度及浓度程长积等参数设置对仿真光谱的影响,通过大气温度对仿真光谱的影响研究解释了特征峰消失和反转现象;通过浓度程长积对仿真光谱研究解释了饱和现象。本文的方法可以应用于各种污染气体的光谱仿真、探测和识别。     

考虑可折叠集装箱的空重箱协同运输优化研究

目的针对集装箱供需矛盾的日益突出,以及空重箱长期独立运输等问题,研究空重箱的协同运输过程,以减少运输资源的浪费。方法在使用折叠式集装箱的情况下,为实现门到门的高效服务,以运输公司总利润最大为目标,建立空重箱协同运输优化模型,并通过LINGO建模求解具体算例。结果通过算例分析,验证了模型的可行性,并与是否使用折叠式集装箱、是否考虑空重箱协同运输等多种模式进行对比。结果发现,在一定条件下相对于传统的运输模式,平均运力利用率提高了15.23%。结论验证了使用折叠式集装箱的空重箱协同运输的经济效益高于其他运输模式。     

Minimizing Stress and Distortion for Shafts and Discs by Controlled Quenching in a Field of Nozzles

A coupled gas‐dynamical and thermo‐mechanical model for simulation of the gas flow, gas and specimen temperature, phase, stress, strain, and displacement transient‐fields during quenching of cutting discs and shafts of steel is introduced. The material properties (e. g. density, conductivity, heat capacity, hardness) are obtained by homogenization procedures. The material behaviour is described as an extension of the classical J₂‐plasticity theory with the extension of temperature and phase fraction dependent yield criteria. The coupling effects such as dissipation, phase transformation enthalpy, and transformation induced plasticity (TRIP) are considered. Simulations were carried out for cutting discs of knives, and for shafts made of steel SAE 52100 with varying diameter. For the validation of the simulations, these work pieces were heated in a roller hearth kiln up to 850 °C, and than quenched in a field of nozzles in which the heat transfer coefficient was known and could be locally adjusted by the volume flow of each nozzle. The phase fractions, surface hardness, distortion, and residual stresses were measured. The simulated and measured results fit quite well. According to optimization‐simulations the shafts were quenched with a certain heat transfer coefficient distribution. The bigger diameter parts of the shaft were more intensively quenched by an increased gas flow so that the hardness profiles were equalized and the residual stresses at the edges were significantly reduced.     

Measurement of the gas-flow reduction factor of the KATRIN DPS2-F differential pumping section

The gas-flow reduction factor of the second forward Differential Pumping Section (DPS2-F) for the KATRIN experiment was determined using a dedicated vacuum-measurement setup and by detailed molecular-flow simulation of the DPS2-F beam tube and of the measurement apparatus. In the measurement, non-radioactive test gases deuterium, helium, neon, argon and krypton were used, the input gas flow was provided by a commercial mass-flow controller, and the output flow was measured using a residual gas analyzer, in order to distinguish it from the outgassing background. The measured reduction factor with the empty beam tube at room temperature for gases with mass 4 is 1.8(4) × 10⁴, which is in excellent agreement with the simulated value of 1.6 × 10⁴. The simulated reduction factor for tritium, based on the interpolated value for the capture factor at the turbo-molecular pump inlet flange is 2.5 × 10⁴. The difference with respect to the design value of 1 × 10⁵ is due to the modifications in the beam tube geometry since the initial design, and can be partly recovered by reduction of the effective beam tube diameter.     

Simulation and experimental studies on plasma temperature, flow velocity, and injector diameter effects for an inductively coupled plasma

An inductively coupled plasma (ICP) is analyzed by means of experiments and numerical simulation. Important plasma properties are analyzed, namely, the effective temperature inside the central channel and the mean flow velocity inside the plasma. Furthermore, the effect of torches with different injector diameters is studied by the model. The temperature inside the central channel is determined from the end-on collected line-to-background ratio in dependence of the injector gas flow rates. Within the limits of 3% deviation, the results of the simulation and the experiments are in good agreement in the range of flow rates relevant for the analysis of relatively large droplets, i.e., ～50 μm. The deviation increases for higher gas flow rates but stays below 6% for all flow rates studied. The velocity of the gas inside the coil region was determined by side-on analyte emission measurements with single monodisperse droplet introduction and by the analysis of the injector gas path lines in the simulation. In the downstream region significantly higher velocities were found than in the upstream region in both the simulation and the experiment. The quantitative values show good agreement in the downstream region. In the upstream region, deviations were found in the absolute values which can be attributed to the flow conditions in that region and because the methods used for velocity determination are not fully consistent. Eddy structures are found in the simulated flow lines. These affect strongly the way taken by the path lines of the injector gas and they can explain the very long analytical signals found in the experiments at low flow rates. Simulations were performed for different injector diameters in order to find conditions where good analyte transport and optimum signals can be expected. The results clearly show the existence of a transition flow rate which marks the lower limit for effective analyte transport conditions through the plasma. A rule-of-thumb equation was extracted from the results from which the transition flow rate can be estimated for different injector diameters and different injector gas compositions.     

瓶体内表面制备类金刚石膜流场结构的格子波尔兹曼模拟

类金刚石膜(Diamond-like Carbon,DLC)具有优异的气体阻隔性能.在PET瓶体内表面制备DLC阻隔涂层时,阻隔涂层的均匀性会受到瓶体内流场结构(气压分布、速度分布等)的显著影响.本文应用格子波耳兹曼方法(Lattice Boltzmann Method/Model,LBM)对PET瓶体内制备DLC阻隔涂层时的流场结构进行模拟,研究了送气速度、气体运动粘度系数和装置结构变化时瓶体内部流场结构的变化.研究结果表明,降低进气速度和提高气体运动粘度系数有利于减弱回流而获得层流结构;装置结构的调整能够改变瓶体内的流场结构,采用恰当的异型装置可以获得较理想的流场结构,对实验工作具有一定的指导意义.     

基于流体体积函数模型的横板型稳压罐内气液两相流场仿真研究

针对水流量标准装置中横板型稳压罐,基于Navier-Stokes方程建立罐体计算流体动力学仿真模型。使用湍流模型、流体体积函数瞬态模型和有限体积法进行离散,并在近壁区采用标准的壁面函数法进行修正,完成横板型稳压罐内部两相流场的数值模拟。数值结果显示空罐充水流态依次经过无水状态-射流-上壅-漫流-稳定状态,同时形成掺气现象和泡状流;气液体积比1:3情况下,满罐充水流场有固定周期的晃荡现象,上侧形成逆时针转动的漩涡气腔,流场湍流粘度较小,分布较均匀,稳定效果最好。     

湍流模型在大钢锭中间包内流场数值模拟中的适应性研究

以多炉连浇大钢锭中间包为研究对象,采用标准k-ε模型和Realizable k-ε模型对大钢锭中间包内钢液流动状况进行了数值模拟,并将数值模拟结果与物理模拟结果相比较,以验证模拟结果的准确性。研究结果表明,对于深熔池、大通钢量的大钢锭中间包,采用Realizable k-ε模型的模拟结果与物理模拟结果更为接近,且对安装控流装置的中间包内流场模拟效果更好。     

RH真空精炼吹氩参数对循环流动影响的数值分析

为研究RH真空脱气过程中的流动行为,建立了描述气泡驱动下的RH循环气-液两相流动的数学模型.基于欧拉-欧拉两流体模型,利用计算流体力学(CFD)商业软件FLUENT6.0,对不同充气量条件下的循环流量进行了预测.计算结果与实验数据的比较表明两者具有较好的一致性.应用该模型对充气压强与循环流量、充气量与上升管内气相及液相速度分布关系进行了数值模拟,用以理解其中的流动规律,为工程技术改进提供参考.