Effects of turbulence on heat and mass transfer in stagnation flows

The influence of turbulence on local heat and mass transfer is systematically analyzed. Essential prerequisite is the availability of measurement methods, based on convective mass transfer, which allow the visualization of heat and mass transfer distributions. The results show that, even at low turbulence intensities, the flow and transport phenomena are decisively influenced by the specific design of turbulence grids and the orientation of the grid wires with respect to the stagnation line. Thereby, two different flow mechanisms occur which may interact. The anisotropy of grid turbulence leads to the “wire-gap effect” depending on the actual position of the grid wires in relation to the stagnation line. The other mechanism is based on the wavy wake velocity distribution behind screens and grid which, in conjunction with the centrifugal instability of stagnation flows, may lead to longitudinal vortices. The results indicate why turbulence has not been sufficiently considered in the available (semi-) empirical correlations. Information needed for an accurate prediction of heat and mass transfer in turbulence flows is discussed.     

橡胶大软管的研制

介绍农用喷粉机用橡胶大软管的结构，模具设计及生产工艺，该产品达到了质量要求，可代替进口产品。     

Effect of microcrystallization on corrosion resistance of AZ91D alloy

Corrosion behavior of cast, homogenized (T4) and microcystallized (mc) AZ91D alloy was investigated in NaCl aqueous solution by gas collection and electrochemical measurement. The capacitance property of the product films formed on mc alloy and cast alloy was studied by Mott-Schottky approach. The results implied that the grain size have a significant influence on the corrosion resistance of AZ91D alloy as well as β phase. The product films behaved as P-type semiconductor with the increasing of anodic potential. TEM observation indicated that the particle size of the product film on the mc alloy (<10 nm) was far smaller than that on the cast alloy (200 nm), which might be beneficial to the widening of energy band and the decreasing of acceptor concentration in the product film on mc alloy.     

建设大型国产磺化装置

对我国建设大型国产磺化装置的必要性及可行性进行了分析。阐明了目前我国大型磺化装置的现状和发展趋势。指出了我国建设大型磺化装置的优势及市场竞争力。     

大型互感器灌封材料的研究

本文介绍一种大型互感器用灌封材料,研究结果表明:该材料体积电阻率为4.7×1016Ω.cm、拉伸剪切强度18.4 MPa、抗冲击强度12.8 kJ.m-2、弯曲强度86.3 MPa、线性膨胀系数为2.98×10-5L.K-1。70℃时粘度低于90Pa.s。     

大型煤化工装置汇总氧阀的研发和应用

叙述了化工装置中用于超纯氧气和氮气介质条件下的高温高压硬密封切断球阀的特点和应用情况,对硬密封氧阀故障原因进行了分析,并给出了改进改进方案。     

大型LNG低温储罐施工技术

在专项调研的基础上,着重介绍了大型LNG低温储罐的施工技术。     

Comparison of cleaning of toothpaste from surfaces and pilot scale pipework

Experiments have been conducted to study the cleaning of toothpaste at two length scales. Laboratory scale cleaning studies have been conducted on fouled coupons in a horizontal flow cell. At pilot scale, the cleaning of fully fouled pipes has been studied and monitored by temperature, conductivity and turbidity probes. Removal from the pipe occurs in two steps: core removal, leaving a thin wall layer that is then removed by thin film removal that takes the majority of the cleaning time. At both scales, cleaning time is influenced by temperature and velocity of the cleaning fluid. The pipe length range studied, 0.3–2 m, does not appear to have a significant impact on cleaning time. Cleaning time correlates well with (shear stress)^?1. A dimensionless cleaning time is defined and a correlation between cleaning time and Reynolds number developed.     

基于Aspen Plus的超大规模甲醇合成工艺模型

利用Aspen Plus对超大规模甲醇合成工艺进行了全流程模拟。模型模拟得到了粗甲醇的成分、反应器出口组成、碳效率、循环比,揭示了循环比对粗甲醇中甲醇摩尔流速、整个反应碳效率、循环气压缩机功率、合成气压缩机功率的影响。通过该模型能够为工艺方案比选、优化设计提供模拟和预测。     

浅谈大型储罐倒装施工技术

本文以兰州-郑州-长沙成品油管道工程——郑州站5万m3钢制内浮顶油罐倒装法施工为例,重点介绍液压提升系统在大型储罐施工中的使用方法和注意事项。以期为以后大型储罐施工提供一定的借鉴作用。     

大型箱形柱的制造

1概述随着我国石油化工工业的不断发展,炼油行业重油催化裂化装置的规模不断扩大,目前重油催化裂化装置的规模已达到300万t/a,其反再框架也逐步由钢筋混凝土结构改为钢结构,其中的反再框架再生器主立柱由于运行载荷大而采用了较大的横截面。本文结合海南炼油项目续建工程280万t/a重油催化裂化装置再生器框架的主要承重立柱为例,阐述大型箱形柱制造的质量控制方法及制造工艺。海南炼油项目续建工程中,280万t/a重油催化裂化装置再生器框架的4根主要承重立柱为H形/箱型组合结构,其截面为H形钢两侧加盖板(相对于H形钢的腹板、翼板,两侧的盖板…     

大型钢丝胶带提升机国产化及技术新进展

1大型钢丝胶带提升机国产化及其应用扫描 “九五”计划末期，我国水泥工业开始进行产业结构调整，确立了“上大改小”，大力发展新型干法水泥的方针，提出通过引进、消化、自主研发等途径，逐步实现水泥技术装备大型化、国产化、现代化，中国水泥工业开始进入一个新的高速发展时期。当时我国已具备相应的工程设计和主机设备加工制造能力，并逐步朝着大型化发展。但大高度胶带斗式提升机几乎完全依赖进口，供应商主要是德国的两家公司．日本某公司的板链提升机（两级提升输送人窑生料）也占有一定市场份额。由于没有国产设备可供选择，市场被国外制造商垄断，价格十分昂贵，因此，不仅增加国内新线建设成本，同时，也成为影响国内对海外水泥生产线总承包项目效益和竞争力的因素之一。如能迅速实现国产化，市场前景广阔，经济效益和社会效益显著。     

大型网架结构的制作与安装

郑州航海体育场钢索膜屋盖工程看台钢结构(网架型式)制安及新技术开发应用。     

大型贮罐搅拌装置的设计

本文通过实例介绍了大型贮罐设计的刚度、强度问题及搅拌器的合理排布。     

国产大型翻盘式过滤机故障处理与改进措施

针对PFS120A翻盘式过滤机运行中出现的内转盘腐蚀、滤盘真空室底板开裂、内外转盘轨道磨损跑偏等问题,进行故障处理,并介绍改进措施。实践表明,技改措施可行,满足了湿法磷酸装置生产的要求。     

大型转化器在PVC生产中的应用

介绍了3种氯乙烯转化器在PVC生产中的使用情况,总结了小列管转化器的特点,指出了大型化和小列管化是转化器的发展趋势。     

大规模采空区灾害控制技术研究

利用RFPA模拟软件分析房间矿柱在大范围岩层移动和应力集中控制作用的基础上,提出了应用隔离矿柱控制采空区连锁式破坏的设想,并进行了数值模拟;在此基础上以较低强度条带充填体代替隔离矿柱,同样有较好的效果。     

大尺寸陶瓷膜原子层沉积过程的CFD模拟

陶瓷膜具有耐高温、耐酸碱、强度高等优点,在液体分离领域得到了广泛应用。对陶瓷膜进行表面改性,可进一步提升其性能,但基于表面化学反应的改性方法工艺过程复杂,难于控制。原子层沉积（atomic layer deposition,ALD）是基于表面自限制化学反应过程的气固相薄膜沉积技术,可以在纳米尺度精确调控孔道结构,特别适用于多孔分离膜的改性和功能化。目前尚无适用于大尺寸陶瓷膜的ALD设备,需要对ALD过程进行专门的优化设计。通过CFD模型对1 m长的单通道陶瓷膜的ALD过程进行了研究,在数学模型中考虑了两种气体源交替进入腔体中所引发不同的表面反应,并考虑了脉冲边界的影响。模拟计算结果与实验比较平均相对误差为1.69%。在数值模拟的基础上,提出了双向交替旋转脉冲的ALD模式,为陶瓷膜的ALD沉积改性的装备设计和过程优化提供了理论依据。