底吹钢包气-钢-渣三相流过程离散-连续转化及联合算法

针对底吹钢包内气-钢-渣三相流过程中小尺度离散气泡和较大尺度自由界面共存的问题,本文采用离散气泡模型模拟小尺度气泡,而对较大尺度气泡和渣层的上下表面则采用界面追踪法直接求解,并采用大涡模拟方法以更好地描述其中的非稳态流动规律.同时,建立离散气泡和大尺度连续气体的转化模型,实现离散-连续联合的多尺度多相流数值计算方法.模型可以同时完整地描述大尺度连续界面和小尺度离散气泡的运动行为;较完善地揭示了小尺度离散气泡的合并过程,离散气泡和连续界面的相互作用及聚合过程,大尺度气泡的运动、变形及合并破碎过程,渣层波动、渣滴及渣眼的形成及演变过程等,并对比实验结果验证了模型的可靠性.     

气泡尾流去除钢液中夹杂物机理的水模型研究

采用水模型和高速摄像机研究了气泡尾流去除夹杂物的过程,分析了气泡尾流去除夹杂物的规律和气泡大小及夹杂物的尺寸和浓度对气泡尾流去夹杂的影响。结果表明,气泡尾流有利于促进夹杂物上浮;气泡尾流中存在尾流边界区和上升区;尾流去除夹杂物的过程分为3个子过程:(1)夹杂物靠近和进入气泡尾流边界区产生扰动;(2)进入气泡尾流上升区和(3)夹杂物继续上升或脱离气泡尾流上升区;气泡直径D_b和粒子浓度C_p增大有利于尾流去夹杂;粒子直径D_p越小越容易被尾流去除。     

连铸坯皮下气泡缺陷成因及控制

皮下气泡是连铸坯常见的质量缺陷,严重影响钢材的质量及使用性能。通过对国内部分钢厂生产的连铸坯皮下气泡的缺陷情况进行总结分析,发现一氧化碳气泡缺陷和氩气泡缺陷占很大比例。其次,总结概述了连铸坯皮下气泡缺陷的分布特点,气泡被捕获的机理以及不同类型气泡缺陷的形成原因,发现脱氧不良、水口吹氩工艺、电磁搅拌以及过热度等均会对皮下气泡缺陷造成影响。为降低铸坯皮下气泡缺陷产生的不良影响,提出了控制连铸坯皮下气泡缺陷的有效措施,以期为实际生产提供参考。     

IF钢铸坯皮下小气泡分布

通过铸坯取样分析研究了板坯结晶器内拉速和电磁制动与小气泡分布之间的关系,探讨了拉速以及电磁制动对IF钢铸坯皮下气泡大小、数量和分布的影响规律.实验结果表明:铸坯皮下气泡直径小于0.1mm的气泡占总数的57%,0.1~0.5mm之间的占42.5%,大于0.5mm占0.5%,并且随着皮下距离的增加,被捕捉的气泡尺寸越来越小,而气泡数量边部比1/4处要多50%左右,1/4位置最少;拉速提高会导致气泡尺寸变小,在1/4及边部,气泡聚集位置由皮下9mm变为12mm附近,但是低拉速和高拉速均在皮下3mm位置处有气泡聚集;电磁制动下,铸坯中心处气泡尺寸变大,1/4及边部位置气泡尺寸变小,且会使气泡数量总体降低,主要表现在聚集位置处的气泡数量明显减少.      

电渣冶炼高氮钢气泡产生的机理及控制

针对高氮钢电渣重熔冶炼过程中出现的气泡缺陷,从气泡产生的位置、宏观形貌及生产现场条件等方面进行了分析,并提出了相应的控制措施。认为材料成分体系及烟罩的气密性是造成电渣锭气泡缺陷的主要原因。通过优化成分体系、改善设备的气密性等措施,有效解决了高氮钢气泡溢出的问题,获得了质量良好的电渣锭。     

浮选三相流中气泡运动特性的数值模拟

为获取浮选气泡在矿浆中的运动规律及三相流中浮选气泡的最佳尺寸,运用欧拉模型模拟不同初始直径的气泡在不同密度矿浆中的运动过程.结果表明:在给定的初始条件下,同一浓度的矿浆中,单个浮选气泡所能捕获的矿物量以直径4mm的气泡最多,气泡尺寸增大或减小后,其矿物捕获量都有所减少.当矿浆中固相质量分数在20%~40%之间变化时,矿物捕获量最多的气泡尺寸变化不大,并且随着矿浆中固相质量分数的增大,单个气泡的捕获量增大,矿物粒子回收率增加.在实际生产中,直径为3.5~4 mm的中等大小气泡在运动过程中变形程度小,气泡水平偏移及浮升速度适中,对矿物粒子的捕获率及运载能力和浮升能力较强,有利于提高浮选产量和质量.      

析气界面上气泡滑移促进的传质模型探索

本文在充分研究析气界面上气泡行为的基础上，根据界面上析出气泡的动力学行为，结合界面附近流体及相间传质理论，导出了气泡滑移促进的传质模型。     

WDH型气泡雾化喷嘴的流量特性研究

WDH型气泡雾化柴油、重油、渣油及奥里油燃烧器已在各行业的工业炉窑上得到了广泛的应用。本文对WDH型气泡雾化喷嘴的流量特性进行了实验研究，此项研究结果对进一步开发WDH型气泡雾化喷嘴的应用领域将发挥重要的作用。     

RH真空室内气泡行为的研究

Ruhrstahl-Hereaeus (RH)上升管内的气液两相流是整个装置的重要动力源,并对钢液的流动、混匀及精炼过程有重要影响.上升管及真空室内的气液两相流决定了钢包内钢液的流动状态,为了研究真空室及上升管内气液两相流,通过1:6的300 t RH的物理模型模拟了RH上升管及真空室内气泡行为过程,并测量了RH循环流量的变化用于计算上升管内含气率以及气泡运动速度最终得到气泡在真空室内的停留时间,同时记录了气泡在真空室内的存在形式.气泡在真空室的存在形式的主要影响因素为提升气体流量,研究发现了气泡从规则独立的大气泡经历聚合长大,碰撞破碎成小气泡,最后变成小气泡和不规则大气泡共存的现象.液面高度达到80 mm之后,气泡在真空室内的停留时间达到一个平衡值,不再随真空室液面高度的增加而发生改变.当提升气体量达3000 L·min-1,气泡停留时间减小趋势弱,对应3000 L·min-1情况下,真空室内气泡开始聚合长大.研究认为对于300 t RH的真空室液面高度应为80 mm,提升气体量应在3500 L·min-1左右,优化后,脱碳时间由原工艺的21.4 min缩短至现工艺的17.5 min.      

液压系统中的气泡

分析液压系统中气泡的产生原因,及造成的不良后果．最后阐述了工程机械液压系统中防上气泡产生的措施。     

韶钢宽板连铸坯气泡产生的原因与对策

通过对韶钢第三炼钢厂宽板连铸坯气泡产生的原因进行分析，制定并实施减少连铸坯气泡的措施，使气泡轧制废品发生率由1．66％减少到0．17％。     

The effect of gamma ray penetration on angle-dependent sensitivity for pinhole collimation in nuclear medicine

The sensitivity of a pinhole collimator for gamma ray imaging in nuclear medicine is dependent on the angle of incidence of the gamma rays. The effect of penetration near the pinhole aperture on angle-dependent sensitivity was investigated using experimental measurements and numerical modeling. Projection data measurements were acquired with Tc-99m and I-131 point sources using tungsten pinhole inserts with 1.0 to 4.0 mm diameter apertures. Curves of the form sinx theta, where theta is the angle of the incident ray with the surface of the detector crystal, were fit to sensitivity measurements from the projection data. Experimentally measured x values were between 3.3 and 4.1 for Tc-99m and between 5.1 and 7.2 for I-131. Penetration near the pinhole aperture was modeled using (1) an expression for effective pinhole diameter that is a generalization of Anger's formula for normally incident photons and (2) a photon transport simulation code. Experimentally measured sensitivity exponents x from new and previously reported experimental observations were modeled within 15% by the numerical simulations. For modeling using the generalized expression for effective diameter the average error was 1.4% and the standard deviation was 7.7%. For the photon transport simulation code the average error was 1.5% and the standard deviation also was 7.7%. The effect of pinhole aperture design parameters on angle-dependent sensitivity for high resolution pinhole apertures was modeled using a photon transport simulation code. The sensitivity exponents x were greater for 364 keV photons than for 140 keV photons and were greater for small aperture diameters, small acceptance angles, and large aperture channel heights. These results provide theoretical justification for incorporating sinx theta sensitivity corrections, with x greater than the value of 3 for an impenetrable pinhole, in filtered back projection and iterative reconstruction algorithms for single photon emission computed tomography (SPECT) pinhole imaging. Simulated I-131 SPECT studies for uniformly active cylinders showed that activity concentrations were underestimated toward the outside of the cylinders when a sin3 theta rather than the correct sinx theta sensitivity correction was applied in image reconstruction.     

在线针孔检测装置在Achenbach铝箔分卷机上的应用探讨

论述了铝箔针孔的检测方法和装置,系统分析了装置的结构和检测原理,提出了在线分析的可行性和具有的优势。     

Breast tumour imaging using incomplete circular orbit pinhole SPET: a phantom study

Improvements in 99Tcm-sestamibi breast lesion visualization using single photon emission tomography (SPET) may help define the clinical role of this technique alongside X-ray mammography in the diagnosis and management of breast cancer. Pinhole SPET offers the advantages of high resolution and sensitivity when compared to conventional parallel-beam collimation for sources located near the pinhole aperture. In this work, the potential of incomplete (180 degrees) circular orbit (ICO) SPET with pinhole collimation is investigated as a means to visualize small (6.4 and 9.6 mm diameter) spherical simulated tumours, at clinical count densities and tumour-to-background ratios, in a breast phantom. ICO pinhole SPET is compared to complete circular orbit (CCO) pinhole SPET for reference, and planar breast imaging (scintimammography) using parallel-beam and pinhole collimators. A prototype box-shaped pinhole collimator with a 4 mm diameter circular aperture was used to acquire projections of an 890 ml breast phantom both in isolation and mounted on a cylinder filled with a mixture of 99Tcm-pertechnetate and water. A heart phantom containing 99Tcm activity in the myocardium was placed in the cylinder. Simulated tumours containing 99Tcm were placed in the breast phantom and scanned at clinically relevant count densities and scan times with tumour-to-normal tissue concentration ratios of 5.0:1 (9.6 mm sphere) and 7.7:1 (6.4 mm sphere). Phantom data were reconstructed using pinhole filtered backprojection (FBP) and maximum likelihood-expectation maximization (ML-EM). The tumours were not visualized with scintimammography, in which lesion contrast and signal-to-noise were estimated from region of interest analysis to be < 2% and 0.01, respectively. Average (over lesion size and scan time) contrast and signal-to-noise in the ICO (CCO) SPET images were 33% and 1.72 (34% and 1.3), respectively. These values indicate that ICO pinhole SPET has the potential to improve visualization of small (< 10 mm) breast tumours when compared with scintimammography, which may be beneficial for the early classification of cancers of the breast.     

莱钢异形坯皮下针孔产生原因分析及控制措施

系统研究了莱钢异形坯皮下针孔产生机理和影响因素,并在LF精炼炉增设定氢仪,对进、出站钢水进行定氢,为解决针孔缺陷提供技术参考和分析依据,通过优化转炉冶炼操作前移工艺、炉渣改质后移工艺、钢水配碳工艺等措施,钢水终点氢含量控制在6ppm以内,基本杜绝雨季时异形坯皮下针孔缺陷。     

Myocardial infarction in rats: high-resolution single-photon emission tomographic imaging with a pinhole collimator

The purpose of this study was to evaluate the accuracy of myocardial imaging by means of high-resolution single-photon emission tomography (SPET) with a pinhole collimator in rats with experimental infarction. Myocardial infarctions were induced in male Wistar rats by ligation of the left coronary artery for 30 min, followed by reperfusion. Two days after the reperfusion, pinhole SPET was performed after the intravenous administration of 111 MBq of thallium-201 chloride, using a rotating gamma camera equipped with a pinhole insert (2.0-mm aperture) in a low-energy pinhole collimator. SPET projection data were collected at 6 degrees increments over 360 degrees using a 4-cm radius of rotation to reconstruct the short- and long-axis images. Projection data were acquired in 15 or 30 s, the SPET imaging being accomplished within 40 min after the injection of 201Tl. After SPET, the rats were sacrificed to remove the hearts for autoradiography (ARG) and nitroblue tetrazolium (NBT) staining as a visual correlative study. Quantitative correlative studies between pinhole SPET and ARG were performed with linear regression analysis for infarct size and distribution properties (relative counts on SPET images and relative density on autoradiographs) on the short-axis sections. All infarcts (4 mm in minimum diameter) in seven rats were detected by pinhole SPET. The SPET images in rats with or without myocardial infarction were consistent with the findings of ARG and NBT staining. There were significant correlations between pinhole SPET and ARG with respect to the infarct size (r=0.933, P <0.001; n=15) and the relative radiotracer distribution (r=0.931, P <0.001; n=68). This study therefore confirmed the accuracy of myocardial pinhole SPET imaging in rats with myocardial infarction. This method may partially substitute for ARG and prove useful for assessing new myocardial imaging agents in vivo in small laboratory animals.     

An analytic model of pinhole aperture penetration for 3D pinhole SPECT image reconstruction

Photons penetrate the attenuating material close to the aperture of pinhole collimators in nuclear medicine, broadening the tails of point spread functions (PSFs) and degrading the resolution of planar and SPECT images. An analytic approximation has been developed that models this penetration contribution to the PSF for knife-edge point pinhole apertures. The approximation has the form exp(-gamma r), where r is the distance on the detector surface from the projection of the point source through the pinhole. The rolloff coefficient gamma is a function of the photon energy, point source location and the design parameters of the collimator. There was excellent agreement between measured values of gamma from photon transport simulations of I-131 point sources (364 keV emission only) and theoretical predictions from the analytic formula. Predicted gamma values from the analytic formula averaged 25% greater than measured values from experimental I-131 point source acquisitions. Photon transport simulations were performed that modelled the 364 keV and less abundant 637 and 723 keV emissions and scatter within the scintillation crystal. Measured gamma values from these simulations averaged 12% greater than the experimental values, indicating that about half of the error between the analytic formula and the experimental measurements was due to unmodelled 637 and 723 keV emissions. The remaining error may be due in part to scatter in the pinhole region and backscatter from gamma camera components behind the scintillation crystal. The analytic penetration model was used in designing Metz filters to compensate for penetration blur and these filters were applied to the projection data as part of 3D SPECT image reconstruction. Image resolution and contrast were improved in simulated and experimental I-131 tumour phantom studies. This analytic model of pinhole aperture penetration can be readily incorporated into iterative 3D SPECT pinhole reconstruction algorithms.     

基于机器视觉的透射式薄带针孔检测系统

给出一种基于高亮度单波长LED光源和高速线阵相机的透射式针孔检测系统。光源的透射光穿过带材上的孔洞,在图像上形成孔洞的亮斑区。由于铝板面的强反光性,环境光的干扰以及采集触发信号启动,也会在图像上产生一些亮的异常部分。利用图像分割算法定位出图像异常部分后,采用特征判别分类缺陷,判别其是否为孔洞,最后计算缺陷在带材上的位置。大量现场数据测试表明该实时孔洞检测系统是稳定可靠的。     

Whole-body and pinhole bone scintigraphic manifestations of Reiter''s syndrome: distribution patterns and early and characteristic signs

The characteristic whole-body and pinhole scintigraphic manifestations of osteo-enthesopathy and arthropathy in Reiter's syndrome (RS) are described, with an emphasis on early diagnosis. We analysed 59 sets of whole-body and pinhole bone scintigrams of 59 patients with RS. The population comprised 47 men and 12 women with an age range from 15 to 53 years (mean=29.4). Bone scintigraphy was carried out 2-2.5 h after intravenous injection of technetium-99m hydroxydiphosphonate using a single-head gamma camera (Siemens Orbiter Model 6601) with a low-energy high-resolution and a 4-mm pinhole collimator for whole-body and pinhole scintigraphy, respectively. In total 262 lesions of osteo-enthesopathy and arthritis were detected on 59 whole-body scintigrams, an incidence of 4.4 lesions per patient. As anticipated, the lesional distribution was asymmetrical: 68% were in the lower limb skeleton and 32% in the axial and upper limb skeleton. Pinhole bone scintigraphy, applied selectively to one region of interest in each case, enabled us to accurately diagnose arthritis and osteo-enthesopathy. It was noteworthy that osteo-enthesopathy, alone or in combination with arthritis, occurred in 78.9%, and had a strong predilection for the foot bones, especially the calcaneus (25. 6%). Pinhole scintigraphy detected enthesopathy in the absence of radiographic alteration in 14.1% of cases and portrayed characteristic signs of RS in 6.9%. Whole-body bone scintigraphy augmented with pinhole scintigraphy was found to be useful in order to panoramically display the systemic involvement pattern, to assess the characteristic bone and articular alterations and to detect early signs of RS.     

Study on Surface Morphology of GaN Growth by MOCVD on GaN/Si(111) Template

The surface morphology of GaN grown by MOCVD on GaN/Si template was studied. Rough morphology and deep pinhole defects on some surface areas of the samples were observed and studied. The formation of rough morphology is possibly related to Ga-Si alloy produced due to poor thermal stability of template at high temperature. The deep pinhole defects generated are deep down to the surface of MBE-grown GaN/Si template. The stress originated from the large thermal expansion coefficient difference between GaN and Si may be related to the formation of the pinhole defects. The surface morphology of the GaN can be improved by optimizing the GaN/Si template and decreasing the growth temperature.