花丝内插物强化竖直管内凝结换热的实验研究

1前言大空隙率多孔体管内插物-绕花丝内插物，被认为是强化管内凝结换热的最有效途径之一[1]．但以往的研究，由于实验雷诺数范围较小，蒸汽速度较低，要正确全面评价其性能尚显不够。本文在原有工作的基础上，进一步完善了实验系统，改进了测试手段，扩大了实验雷诺数范围，并测试了其阻力性能，对花丝内插物强化管内凝结换热进行了较深入全面的实验研究，以全面评价花丝内插物对管内凝结换热的强化效果。2实验系统本文实验系统如图1所示。实验段是一个竖直套管冷凝器，如图2所示．本试验研究蒸汽完全凝结时的传热。凝结水流量采用容积法计…     

Static and dynamic detection of axial surface defects on metallic wires by conical triple laser reflection

The quality of the surface of metallic wires is relevant for different applications. The reflection of a laser beam on the surface of a metallic cylindrical wire provides an efficient way to inspect the quality of its surface. Our interest is focused in the detection of axially oriented defects, which are the most relevant for the wire drawing process. We present a simple interference-geometrical model to describe the light pattern reflected from a wire with defects. This model adequately accounts for the observed results from an industrial prototype developed for the purpose. It incorporates three-laser beams incident on the wire at equidistant locations in its perimeter, which produce three reflection cones with a CCD. This configuration permits to explore the whole perimeter of the wire. Several results are presented, both in static operation and in production line, in agreement with qualitative and quantitative predictions.     

Microstructural and mechanical analysis of Cu and Au interconnect on various bond pads

Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h.     

Analysis of the sensitivity to the electrochemical potential of the width of a metallic nanoconstriction

In relation to a metallic nanowire in the presence of an electrochemical potential, the sensitivity to this potential of the nanowire width is evaluated by defining and calculating a suitable parameter that can be regarded as a normalized gradient, this gradient being the derivative of the above-mentioned width with respect to the electrochemical potential.     

Study of Glow Wire Ignition Temperature (GWIT) and Comparative Tracking Index (CTI) performances of engineering thermoplastics and correlation with material properties

Recent regulation IEC 60335-1 ed.4 (2008) was introduced for materials used in electric appliance, establishing new limits in Glow Wire Ignition Temperature (GWIT) performance for materials used for electric connectors. Development of new products with high GWIT is possible, but the main issue is to keep good mechanical properties and processability, as well as tracking resistance (Comparative Tracking Index-CTI). Only a few patents and scientific publications exist about glow wire test performance of polymers. In this work we report GWIT and CTI properties for three engineering thermoplastic polymers (PBT, PET and PC). We have also studied the phenomena involved in this test, treating the phenomena with the parameterisation approach already used in the studies of the fire behaviour of polymers. PC, PBT and PET filled with 30% w/w glass fibres have been tested, and material properties that can be related to GWIT and CTI performance have been measured by TGA, Laser Flash Thermal Diffusivity (LFTD), Pyrolysis-GC/MS. CTI seems to be correlated with the char formation tendency of the materials, so PBT show a higher tracking resistance than PET and PC. Polycarbonate was the only material that passed the glow wire test (GWIT higher than 775 °C) but generally GWIT performance is not directly related with degradation temperature, since PET is thermally more stable compared with PBT, but less stable in glow wire test. The ignition process, together with the unsteady heat and mass transfer process characteristic of glow wire testing, are affected by many parameters at the same time. That’s why it is not easy to relate results of TGA, Laser flash, Pyrolysis-GC/MS with the glow wire ignition temperature of the materials tested, but the whole of these properties can give useful indication.     

Flow-induced vibration in two-phase flow with wire coil inserts

Information of flow-induced vibration (FIV) in two-phase flow with wire coil inserts at atmospheric pressure, is presented in this study. FIV was measured in an upward vertical tube for four different wire coil inserts using an air–water mixture as process fluid. Vibration increased along with mass flux and quality. The narrower wire coils produced more vibration. The FIV prediction correlation for two-phase flow with wire coil inserts was experimentally developed with coefficient correlation value of 0.956.     

Investigating droplet separation efficiency in wire-mesh mist eliminators in bubble column

Effects of design parameters on performance of wire-mesh mist eliminators were experimentally investigated in 15 cm bubble column. The demisters performances were evaluated by droplet collection efficiency as a function of wide ranges of operating and design parameters. These parameters include: droplet size exiting the demister (250–380 μm), specific surface area (236–868 m²/m³), void fraction (97–98.3%), wire diameter (0.14–0.28 mm), packing density (130–240 kg/m³), and superficial gas velocity (0.109–0.118 m/s. All demisters were 15 cm in diameter with 10 cm pad thickness, made from 316L stainless steel layered type demister pad wires. Experiments were carried out using air–water system at ambient temperature and atmospheric pressure. The experimental data on the droplet removal efficiency were obtained using Malvern Laser Droplet Sizer. The removal efficiency was found to increase with the increasing the demister specific surface area, packing density, and superficial gas velocity. In contrast, the removal efficiency was found to increase with decreasing the demister void fraction and wire diameter. The separation efficiency is correlated empirically as a function of the design parameters. A good agreement was obtained between the measured values and the correlation predictions with ±5% accuracy.     

冲击高度对自由冲击射流影响的实验研究

采用热线风速仪测量了雷诺数为 ２３ ０００时四种冲击高度下率流自由冲击射流流场，并给出详细的结果．表明壁面的“阻尼”影响主要集中在近壁面０．５Ｄ以内．小冲击高度时径向速度下降得比大冲击高度时明显要快，量值也较小；在ｒ／Ｄ≤１．５处，小冲击高度时紊动能的数值大小和分布趋势与大冲击高度时不同，特别是在喷管出口距冲击板高度Ｚ与喷管直径Ｄ之比Ｚ／Ｄ为８时分布特殊，在其它测点处，紊动能的分布趋势基本一致，只是大冲击高度下的值较大；流动结构在Ｚ／Ｄ为６～８时发生了较大的变化，这种变化与势流核心区有关，在势流核心区的顶端以及下游的一段距离内紊流度都很高．     

Spectral finite element of a helix

Determination of a spectral (i.e. frequency dependent) finite element of a helix is the focus of this communication. The helix is treated as straight, linear elastic element, exhibiting coupling of axial with torsional responses. We derive explicit forms of all the coefficients of the stiffness matrix and plot their dependencies on the frequency and the parameter describing the said coupling. In general, the growth of that parameter leads to a progressively denser occurrence of the resonances of both axial and torsional motions.