超音速氧枪射流特性的数值模拟

利用GAMBIT建立了轴向计算长度2 200 mm和径向计算长度800 mm的超音速氧枪的数学模型,并采用FLUENT软件对氧枪射流特性进行数值仿真研究。分析了单孔氧枪超音速射流特性,以及操作压力(0.6~1.0 MPa)和环境温度(298~1 873 K)对流动特性的影响。结果表明,入口滞止压力在设计压力±25%内对射流轴向衰减及径向扩展影响不大,其与射流的超音速区长度呈二次曲线关系变化,随环境温度升高,射流轴向衰减变缓慢,核心区长度增加,超音速区长度和环境温度呈线性关系,环境温度对射流径向影响很小。     

转炉氧枪超音速射流特性的数值模拟

用Fluent软件对炼钢转炉氧枪在不同工况条件和环境温度下的射流行为进行数值模拟研究。结果表明:出口马赫数、环境温度和出口压力对氧气射流影响显著;氧枪射流超音速核心长度与出口马赫数和环境温度呈正相关,与环境气体压力呈负相关;在设计工况下,回归得到无因次超音速核心长度与出口马赫数的关系方程;非设计工况下,随着出口压力的变化,超音速核心长度与出口压力比(Pe/Pa)呈线性关系。此外,进一步研究了转炉内环境温度变化对超音速射流核心长度的影响,通过引入"引射率"分析了射流在传输过程中对周围气体的引射特性,并得到轴向引射率随出口马赫数和环境温度的变化关系。     

对横列轧机预防轧辊破断的见解

继本刊1986年第7期发表的“横列轧机轧辊破断情况的分析”一文之后,作者对某800轧机轧辊破断,在多年考察、分析、验证的基础上,提出了一系列预防轧辊破断的见解。对轧辊的破断,按其受力状态分辊身、辊环、辊脖、接头四个部位。逐项分析了造成破断的原因,并相应地提出了预防破断的措施。     

横列式轧机轧辊破断情况的分析

根据某800横列型钢轧机多年来轧辊破断的基本情况,针对占轧辊破断比数最大者——轧辊接头处破断,抓住横列轧机运转的特点,作了切合实际的力学理论分析。为横列式轧机存在的轧辊破断问题,提供了分析原因和有价值的认识论证,并相应地指出其操作技术上应改进的途径。     

环境温度对超音速氧气射流特性影响的数值模拟

通过数值模拟的方法研究了不同环境温度条件下超音速氧气射流的特性,并与前人的实验结果进行了对比分析.研究结果表明：与低温环境条件相比,高温环境条件下超音速氧气射流的速度衰减受到抑制,射流核心段长度得到延长;不同环境温度条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度;射流的压力分布趋势与射流速度分布趋势一致.数值模拟得到的射流速度、温度和压力结果与实测值吻合度较高.     

中厚板管层流淬火控冷系统水动力学模型

利用水动力学伯努利方程和连续性方程，推导了中厚板管层流淬火与控冷系统水力学性能和结构参数之间关系式。结构参数有水箱高度、管道内径和长度、阻尼孔径和孔数、喷管直径和个数等；性能参数有系统最大流量与最小流量、射流冲击力、射流冲击区直径、射流密实高度、射流不断流长度等。增大集管阻尼和提高水箱高度，是提高喷水均匀性的有效方法。     

高压水射流破碎高围压岩石损伤场的数值模拟

利用ALE(arbitrary lagrange-euler)算法,考虑到一般情况下岩石处于高围压状态,建立了高压水射流冲击高围压岩石的数值模型.分析了高压水射流冲击下高围压岩石的损伤演化过程,指出岩石破碎过程呈阶跃式;通过对比无围压状态下岩石和高围压状态下岩石在高压水射流作用下破碎坑演化情况,指出处于高围压状态下的岩石损伤沿轴向的演化速率明显低于无围压状态下的岩石,沿径向的损伤演化受围压影响较小.通过分析4个典型单元在不同速度射流冲击下损伤演化情况,表明在提高射流速度可明显提高射流破岩效率,并在理论上对射流速度与射流破岩性能的关系进行了解释.     

无接头绳圈破断性能影响关键因素研究

无接头绳圈作为索具被广泛应用于大型结构物海上吊装施工,其编织质量直接影响到海上吊装施工的效率和安全.为找到影响无接头绳圈破断性能的关键因素,本文根据无接头绳圈的性能要求和相关国家标准设计了无接头绳圈破断性能试验方案.通过无接头绳圈破断试验和钢丝拆股试验,研究了捻距、抽芯、疲劳、存放时间及使用次数对无接头绳圈破断性能的影...     

150t转炉五孔氧枪射流特性数值模拟研究

以某钢厂150 t转炉为研究对象,建立了三维数学模型,利用数值模拟方法研究了不同喷孔倾角、喉口直径以及马赫数对五孔氧枪射流特性的影响规律。结果表明：随五孔氧枪喷孔倾角的增加,射流核心段轴向长度减小,氧枪头下方负压区增大,射流向下偏移量减小,到达冶炼枪位时射流速度减小且射流面积增大;随五孔氧枪喉口直径的增大,射流核心段轴向长度增大,到达冶炼枪位时射流速度、射流面积均增大,冶炼枪位时喉口直径41.1 mm的射流速度分别是喉口直径39.9、38.7、37.5 mm的1.01、1.05、1.07倍;随五孔氧枪马赫数的增加,射流核心段轴向长度略微增加,到达冶炼枪位时射流面积稍有减小,但均变化不大。     

谈控制钢丝绳重量

在通常遇到的所有与钢丝绳生产相关资料中,均视钢丝绳重量(确切来讲,应称为钢丝绳质量,为了叙述方便,本文仍沿用钢丝绳重量这一习惯用语),为其基本性质之一,就如同钢丝绳直径、破断拉力、填充系数、临界长度、破断拉力总和等性质一样。事实上,大多数钢丝绳标准并不看重钢丝绳重量,因为在这些标准中并没有将其当作一个技术条件而体现出来,无论是公称重量、计算重量,还是近似重量,要么干脆不提是否考核,要么直     

The influence of particles on jet breakoff

Experimental observations of the breakup of a liquid jet issuing from a vibrated nozzle support the view that particles passing through the orifice tend to create a surface disturbance which, depending on the phase relative to the nozzle vibration, may either add to or subtract from the disturbance created by the nozzle vibration. The result may be either a shortening or lengthening of the jet breakoff length, depending on phase. The implications for sorting large cells with a fluorescence-activated cell sorter are discussed.     

圆形冲击射流对水层的穿透深度研究

要使中厚板淬火控冷装置获得最佳的冷却能力,必须要保证冲击射流可以穿透钢板表面的滞留水层。通过实验和数值模拟的方法,研究了圆形冲击射流对水层的穿透深度与射流速度、射流直径和射流高度的关系,并给出了穿透深度与射流出口弗鲁德数Fr的拟合曲线关联式。     

聚合射流氧枪射流特性的实验研究

利用带有中心主孔的Laval喷管和16个副孔的聚合射流氧枪喷头的氧枪射流检测系统研究氧枪射流中心速度的衰减规律,测试常温氦气代替高温燃烧的保护气体作为伴流而产生的聚合射流,以及高温以主孔通空气,两副孔分别通入氧气和丙烷来产生保护气体模拟的聚合射流。结果表明,聚合射流特性优于传统射流特性,常温下随氦气入口压力增加,中心射流的轴向衰减变缓,获得比传统超音速射流更长的超声速区域;高温下通过调节燃气和氧气流量可改变环状火焰长度,同时可以根据生产实际情况变化主射流长度,满足冶炼工艺要求。     

Computation of continuous cooling transformation diagrams for the heterogeneous nucleation in Sn-5 mass pct Pb droplets

A method was developed to compute continuous-cooling-transformation (CCT) diagrams for the heterogeneous nucleation of alloy droplets from a few experimental data. The developed model addresses both oxidation-catalyzed surface nucleation and internal nucleation caused by another catalyst. Droplet surface oxidation is regarded as a first-order reaction in order to account for the effects of the gradual increase in surface oxidation on the kinetics of surface nucleation. CCT curves were computed for Sn-5 mass pct Pb droplets cooling in atmospheres with various oxidation potentials using data determined with monosize droplets produced by capillary jet breakup. The developed model may be used to predict droplet nucleation kinetics in industrial thermal spraying processes.     

In situ hybridization for the detection of telomerase RNA in the progression from Barrett''s esophagus to esophageal adenocarcinoma

AIMS: To compare the value of the proximal flow convergence method and the jet area method for the determination of the severity of tricuspid regurgitation. METHODS AND RESULTS: The proximal isovelocity surface area radius and the jet area/length were measured in 71 consecutive patients with angiographically graded (grade 0/I-III) tricuspid regurgitation. Rank correlation coefficients with the angiographic grade were 0.71 (P < 0.001) for the proximal isovelocity surface area radius (aliasing border of 28 cm.s-1), 0.66 (P < 0.001) for the jet area, and 0.63 (P < 0.001) for the jet length. The proximal isovelocity surface area radius was significantly correlated with the jet area/length (correlation coefficients 0.82/0.77, P < 0.001). Correct differentiation between mild to moderate (grade I-II) and severe (grade III) tricuspid regurgitation was achieved in 62 of 71 patients (87%) by means of the proximal isovelocity surface area radius, in 61 of 71 (86%) by the jet area, and in 62 of 71 (87%) by the jet length. Grade III tricuspid regurgitation was not identified in five of 21 patients (24%) by means of the proximal isovelocity surface area radius, in six of 21 (29%) by the jet area, and in seven of 21 (33%) by the jet length. CONCLUSION: The flow convergence method and the jet area method are of similar value for the determination of the severity of tricuspid regurgitation. Both methods differentiated mild to moderate from severe tricuspid regurgitation in most patients. However, underestimation of severe tricuspid regurgitation in 20-30% of the cases represents a serious limitation of both methods.     

Monosize droplet deposition as a means to investigate droplet behavior during spray deposition

A Rayleigh atomization technique is employed to produce streams of evenly spaced, monosized droplets of molten metal. We study the effects of variations in selected process parameters upon the droplet formation mechanism and the morphology and microstructure of resulting deposits. Initial tests with alcohol jets show that changes in the flow velocity, drive frequency, and destabilization amplitude have a significant effect upon the efficiency of droplet formation and the uniformity of the droplet stream. For instance, an integer-multiple increase in the flow velocity shifts the frequency threshold for stable jet breakup by an integer multiple of its original value. In addition, the optimal frequency range broadens at higher flow velocities. Microstructural studies on Sn/Pb droplets formed using this approach show signs of rapid solidification.     

Biplane transesophageal color-flow Doppler imaging in assessing severity of mitral regurgitation: influence of hemodynamic circumstances and mechanism of regurgitation

OBJECTIVE: To determine the value of biplane transesophageal echocardiography in the assessment of severity of mitral regurgitation compared with left ventricular angiography. DESIGN: Prospective study of consecutive patients. SETTING: Two university hospitals, one community hospital. PARTICIPANTS: Thirty-seven patients with angiographically proven mitral regurgitation. INTERVENTION: Transthoracic and biplane transesophageal echocardiography. In 19 patients, transesophageal echocardiography was performed during general anesthesia. MEASUREMENTS AND MAIN RESULTS: The largest mitral regurgitation jet area and longest jet as obtained with Doppler color-flow mapping from transthoracic and biplane transesophageal echocardiography and pulsed-Doppler pulmonary venous flow characteristics. Sensitivity and 100-minus-specificity were plotted to constitute receiver operating characteristics (ROC) curves. Areas under ROC curve for transverse, longitudinal, and biplane jet area were 0.77, 0.75, and 0.81, and for jet length, 0.82, 0.84, and 0.88, respectively; this was for biplane jet area in conscious patients; 0.99 compared with 0.72 in anesthetized patients (p < 0.05). CONCLUSIONS: Biplane measurements identified severe mitral regurgitation slightly more reliably than the transverse or longitudinal measurements alone. In conscious patients, jet area was an excellent test for estimating severity of mitral regurgitation. In anesthetized patients, a combination of biplane jet area and length and of systolic pulmonary venous flow reversal accurately predicted angiographic severity of mitral regurgitation. In anesthetized patients, the optimal cut-off value for jet area to distinguish between moderate and severe mitral regurgitation was lower than in conscious patients. In the total population, regardless of hemodynamic and technical variations, a combination of biplane jet area and length and of systolic pulmonary venous flow reversal accurately predicted the severity of mitral regurgitation.