Analysis of the flow field,thermal performance,and heat transfer augmentation in circular tube using different dimple geometrical configurations with internal twisted-tape insert

In this study, a numerical investigation for the fluid flow field analysis using different configuration dimple parameters in conjunction with an internal type insert in pipe is carried out. The effects of the dimple diameters with a center twisted tape on the flow pattern, pressure drop, friction factor, and heat transfer characteristics are investigated. The influence of the latter device on heat performance and thermal-hydraulic performance evaluation factor (PEF) were carried out in a pipe for fully developed flow with range for fully developed flow with range of Reynolds number (Re) of 1573 and 23 592. Experiments with numerical models are performed using different dimpled dimeters by inserting twisted tapes. The outcomes observe that the qualitative analysis for flow fields such as static pressure, dynamic pressure, velocity magnitude, wall shear stress, and turbulent kinetic energy as well as the quantities analysis for pressure drop, heat transfer coefficient friction factor, and Nu number in dimpled pipe fitted with twisted tape are greater than plain pipe. This is because using these devices cause more secondary flow, swirl flow, and flow mixing that lead to higher turbulence, which, in turn, enhance the overall heat transfer. The results indicated that the lower and higher values of thermal PEF are about 0.78 and 1.6, respectively, at the dimple dimmers of 1 mm.     

表面微造型对滑动轴承气穴影响的探究

基于Rayleigh-Plesset方程的气穴模型,研究了微造型对滑动轴承润滑剂中气穴分布规律的影响。为此,分别建立了具有不同位置、尺寸微造型的滑动轴承有限元模型,利用软件ANSYS 11.0着重分析了气化位置、气化面积和润滑剂蒸汽体积率的变化规律。计算结果表明:微造型布置在滑动轴承润滑剂气化区时,蒸汽体积率波动变大,气化面积变小;微造型的几何尺寸对气穴发生位置有显著影响;滑动轴承气化面积越大,其承载力越小,摩擦系数越大。     

镶嵌MoS2的Al2O3/TiC基陶瓷刀具材料微孔表面摩擦磨损性能研究

采用Nd:YAG激光器在Al2O3/TiC陶瓷刀具材料表面加工出不同密度的微孔,并涂覆填装MoS2固体润滑剂,在UMT-2摩擦磨损试验机上进行往复摩擦试验,研究其在不同载荷和速度下的摩擦磨损性能,通过白光干涉仪、光学显微镜和扫描电镜观察激光织构化后表面特征和磨损后表面形貌。结果表明:激光织构化后,陶瓷材料表面发生了氧化;在相同的实验条件下,与光滑表面相比较,填装MoS2固体润滑剂的微孔表面能够有效地降低摩擦因数,减小磨损率。这主要是由于填装在微孔中的润滑剂在摩擦作用下涂覆到基体表面,形成润滑膜,起到减摩降磨作用,同时激光加工后微孔周围凸起及氧化后形成的摩擦特性优良的TiO2也能起到良好的减摩降磨效果。通过对磨损形貌分析,光滑表面磨损较为严重,有大量的犁沟产生,主要的磨损形式为磨粒磨损及脆性断裂;微孔表面磨损较为轻微,其主要磨损发生在微孔周围。     

Corrosive fatigue of structures with dimple holes under spectrum loading

ABSTRACT Experimental investigation and life prediction are made for structures with straight holes and dimple holes in both laboratory ambient conditions and 3.5% NaCl solution under spectrum loading. With the aid of acoustic emission, label loading and fractography technique, the crack‐growth data are obtained in both environments. Stress‐intensity factors for the corner crack emanated from the dimple hole are evaluated by three‐dimensional (3D) finite element (FE) method. Life prediction of the tested structures is made by using the modified FASTRAN‐II code on the basis of corresponding fatigue crack‐growth rate curves. It is shown that once the initial defect size a₀ is determined by one set of test data, it can be used together with the 3D crack‐growth method in order to provide accurate life prediction in alternative structure and loading condition. By comparison, life prediction by the traditional local strain method is also made which is shown to be less reliable than the 3D crack‐growth method.     

考虑横向振动的热弹流润滑分析

数值模拟接触固体的横向振动对点接触热弹性流体动力润滑的影响。结果揭示出接触固体的微小横向振动就会造成接触区中油膜压力、膜厚和温度的显著变化,接触区中产生多重凹陷并不断移动。重载下由于动态效应产生的凹陷的移动和合并及热效应的作用,使得膜厚不但不随载荷的增加而减小,反而随载荷的增加而增加。     

热条件下表面中央凹陷对平面轴承承载力的影响

针对方形滑块平面轴承,建立热条件下的流体动力润滑模型。用有限差分法求解温度场,多重网格法求解压力场,基于几种不同的表面温度条件讨论表面中央凹陷的存在对承载能力的影响,并进一步分析凹陷的尺度对承载力的影响。结果表明:凹陷对承载力的贡献可能是正面的亦可能是负面的,这与表面的温度及凹陷尺度都直接相关。尤其需要指出的是在热楔占主导且边界条件为静止表面常温而运动表面绝热时,中央凹陷会减低承载力,即此时使用表面凹陷织构来提高承载力是不可行的。     

大型薄膜蒸发器夹套结构传热性能数值模拟

利用FLUENT软件对大型薄膜蒸发器夹套结构内流体的传热性能进行数值模拟,通过对比蜂窝结构与整体结构,得出蜂窝结构夹套内温度场和速度场分布均匀,传热性能较整体结构夹套得到了很大提高。采用正交实验理论,分析了蜂窝夹套不同结构参数对传热的影响,得到了合理的蜂窝夹套结构形式。     

仿生硅藻结构圆周位置和间距对轴承润滑性能的影响*

基于硅藻结构,在水润滑轴承表面设计矩形-半球型复合型织构,采用流固耦合的方法研究不同织构位置角度和织构间距下的复合型织构轴承的润滑性能,并与光滑轴承和单层织构轴承润滑性能进行对比。结果表明：复合型织构轴承的摩擦力和摩擦因数始终小于单层织构轴承和光滑轴承,且在织构位置角度超过22.5°~45°范围内的某一角度后,复合型织构轴承的最大水膜压力大于单层织构轴承;在不同间距条件下,随着织构位置角度的增大,复合型织构轴承最大水膜压力呈先增加后减小的趋势,摩擦因数呈现先减小后增加的趋势;在织构间距为5°且织构位置角度为45°时,复合型织构轴承的摩擦学特性最优。     

TENSILE FRACURE IN AN Al-Li ALLOY 8090

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