基于灰色关联度的微孔端面机械密封开启力共性影响参数分析

目前微孔端面机械密封采用的几何参数繁多,缺乏明确物理意义。为找出跨孔型的共性几何参数,基于Fluent多相流空化模型,针对矩形孔、菱形孔、椭圆孔端面机械密封,建立密封间隙流体的三维数值计算模型,计算得到144条开启力数据;在分析开启力和几何尺寸之间的关系、额外开启力产生机制的基础上,提出等效长度和等效宽度2个具有物理意义的几何参数;采用灰色关联度分析法,分析和验证等效长度、等效宽度、方向角、面积比对开启力的影响,发现4个因素对3种微孔密封的间隙流体开启力都有影响,但等效长度与等效宽度的影响较方向角、面积比大。     

油套管铸造阳极防CO2腐蚀工艺实验研究

为了研究在BG110-3Cr套管外表面铸造防腐用环状锌阳极的工艺对套管基体性能及阳极材料性能的影响。采用金属材料拉伸试验法分别对电阻炉加热升温和浇铸热传导所得的2组套管拉伸试件进行机械性能测试后,通过扫描电镜观察断口微观形貌,再用ICP法和直读光谱法检测合金中熔融元素含量。实验结果表明:拉伸件模拟升温至600℃后,抗拉强度和屈服强度分别降低至913.1 MPa和799.4 MPa,断口均匀分布的等轴韧窝聚变为凹坑,屈服强度降低,但韧性增强。实测受铸造传热升温的套管拉伸件抗拉强度和屈服强度分别提高至1015.1 MPa和890.5 MPa,满足API标准要求。该成果为套管表面铸造防腐用耐温牺牲阳极合金及深井套管阴极保护领域应用提供了技术支持和理论依据。     

Fabrication and tribological behaviors of corner-cube-like dimple arrays produced by laser surface texturing on medical needles

Micro-corner-cube-like dimples with various geometrical characteristics were fabricated on the surface of medical needles by laser surface texturing. The effects of geometric parameters of dimples on tribological behaviors were investigated by carrying out insertion tests. It was found that the textured surface with a dimple array increased the friction between the needle and phantom tissue because of stress concentrations near the edges. Furthermore, the drag increment rate increased with the increase of dimple size and circumferential number, while dimple depth had no significant effect on the friction. The minimal drag increment rate was achieved at a medium value of spacing. The geometric parameters of dimples could be varied to control area density that indirectly affect the friction behavior.     

金属断裂韧性与微观参量的关系

根据三轴性应力水平对裂纹尖端塑性应变及韧窝尺寸的影响以及相关关系，导出了材料断裂韧性（ＪＩＣ）与拉伸性能、伸张区宽度（以及韧窝尺寸（直径Ｄ）之间的关系，并得到了实验的验证①．     

均布圆柱形孔活塞环油膜承载力的解析解和数值计算

现有对微织构的研究多采用数值法。相比于数值解,解析解有助于简单清楚的表达微孔活塞环润滑性能的主要影响因素和各物理量的潜在关系,提高设计者的认识。基于入口吸入理论和流量连续性条件,对均布无限个圆柱形微孔的活塞环的一维油膜的空化区分布、压力分布和承载力进行了解析计算,并将一维解析解积分得到了一个周期油膜的承载力。解析解表明均布n个圆柱形微孔活塞环的前n-1孔的压力分布相似,最大压力相等,最大压力与进口压力,孔间间距和空化压力相关,在均布微孔时,孔内最大压力约为进口压力的两倍；第n孔的压力分布和最大压力还与出口压力相关,在均布微孔时,孔内最大压力约为进出口压力之和。还揭示了孔深对空化分布和油膜承载力的影响机理,当孔深大于油膜厚度的一半时,随着孔深的增加,空化区面积减小。使用Fluent软件对均布四个孔的油膜进行了数值模拟,并与解析解作对比。在解析解有解,数值解收敛的范围内,解析计算和数值计算的结果规律一致,解析式能解释数值模拟得到空化区分布、压力分布以及油膜承载力的变化趋势,所获得的在最大油膜承载力时的微孔几何尺寸也与模拟计算一致,油膜承载力的解析解和数值解最大相差10%。     

Numerical investigation on location of protrusions and dimples during slot jet impingement on a concave surface using hybrid ANN–GA

Numerical simulations using ANSYS Fluent 17.2 are explored for a detailed discussion on jet impingement over a compound dimpled and protrusioned concave surface. Previous researchers have proved that both dimples and protrusions help in heat transfer augmentation. However, the combined effect of dimple and protrusion over a concave surface is still not studied, which may show a significant improvement in heat transfer. Therefore, the present study is devoted to the alternate location of dimple and protrusion over a concave surface for enhancement in impingement heat transfer. Simulations are performed for several arrangements of dimples and protrusions over a concave surface. It is noticed that a particular arrangement of dimples and protrusions leads to an increase in heat transfer compared with a fully protruded or fully dimpled concave surface. Furthermore, it is also noticed that protrusions/dimples at the stagnation region degrade overall impingement heat transfer. The wall shear stress profile is found to be similar to its corresponding local Nusselt number profile. Lastly, the optimal location of dimples and protrusions is predicted using an artificial neural network and a specially formulated discrete version of genetic algorithm.     

Computational fluid dynamics-based optimization of dimpled steam cracking reactors for reduced CO2 emissions

Spherical dimples in cylindrical tubes enhance heat transfer and lead to a more uniform radial temperature profile. To combine these positive properties with a low pressure drop, a single dimple was optimized through a genetic algorithm. Multiple design parameters such as width, height, and curvature of the dimple were investigated. Heart-shaped dimples outperformed spherical dimples. Three-dimensional reactive simulations of a Millisecond propane steam cracking reactor showed that both the spherically dimpled and the heart-shaped dimpled coil positively affect the light olefin selectivity, mainly through an increase in propylene selectivity. The optimized dimples could reduce the high pressure drop penalty by 21%. Run length simulations proved that the optimized dimple shape results in an additional run length extension of 18%. Next to this, the fuel rate consumption can be decreased by 6% compared to a bare coil, which could theoretically result in 4% less CO₂ emissions.     

钛合金BT9非比例载荷低周疲劳断口显微分析

在室温下对钛合金BT9比例及非比例载荷下的低用疲劳试验后,利用扫描电镜及透射电镜对材料的疲劳变形结构进行观测.结果表明:在比例载荷条件下,疲劳断口扩展区微现形貌为等轴韧窝,随着应变强度的增加,断口韧窝密度增加,韧窝变深;在非比例载荷条件下,断口扩展区的微现形貌为准解理断裂和解理断裂.随着非比例载荷程度(相位角)的增大,断口的形貌由微孔聚集型断裂向解理断裂方向发展.     

Atomic diffusion properties in wire bonding

1 Introduction Ultrasonic bonding was applied primarily to wire bonding in microelectronic packaging industry, while the mechanism of ultrasonic bonding has not been understood very well. HARMAN[1] observed that the peeling underdeveloped bonds simulate a…     

影响椭圆微孔端面机械密封回吸现象的参数研究

为研究回吸现象对泄漏率的影响,基于Fluent多相流空化模型,建立椭圆微孔端面机械密封间隙液膜的三维数值计算模型,并从原理上分析影响回吸现象的因素。结果表明:回吸越强,泄漏率越低,甚至是零泄漏;回吸现象的影响参数可以分为两类:影响动压效应的参数,如转速、内外径压差、空化压力;造成低压区与密封间隙出口截面间距离改变的参数,如方向角(椭圆长轴与水平轴逆时针夹角)、椭圆形状因子(椭圆长短轴比)。探讨各因素对椭圆微孔端面机械密封回吸现象的影响。结果表明,回吸的强弱与转速、椭圆形状因子正相关,与内外径压差、空化压力负相关,与方向角的关系类似正弦曲线。