Heat transfer and friction factor of Therminol liquid phase heat transfer fluid in a ribbed tube

Experiments and simulations on flow and heat transfer behavior of Therminol-55 liquid phase heat transfer fluid have been conducted in a ribbed tube with the outer diameter and inner diameter 25.0 and 20.0 mm,pitch and rib height of 4.5 and 1.0 mm.respectively.Experimental results show that the heat transfer and thermal performance of Therminol-55 liquid phase heat transfer fluid in the ribbed tube are considerably improved compared to those of the smooth tube.The Nusselt number increase with the increase of Reynolds number.The increase in heat transfer rate of the ribbed tube has a mean value of 2.24 times.Also,the pressure drop results reveal that the average friction factor of the ribbed tube is in a range of 2.4 and 2.8 times over the smooth tube.Numerical simulations of three-dimensional flow behavior of Therminol-55 liquid phase heat transfer fluid are carried out using three different turbulence models in the ribbed tube.The numerical results show that the heat transfer of ribbed tube is improved because vortices are generated behind ribs,which produce some disruptions to fluid flow and enhance heat transfer compared with smooth tube.The numerical results prove that the ribbed tube can improve heat transfer and fluid flow performances of Therminol liquid phase heat transfer fluid.

Friction Behavior of Magnetorheological Fluids with Different Material Types and Magnetic Field Strength

Magnetorheological （MR） fluid is a type of a smart material that can control its mechanical properties under a magnetic field. Iron particles in MR fluid form chain structures in the direction of an applied magnetic field, which is known as MR effect, resulting in variation of stiffness, shear modulus, damping and tribological characteristics of MR fluid. As MR effect depends on the density of particles in the fluid or the strength of a magnetic field, the experiments are conducted to evaluate the friction property under reciprocating motion by changing the types of MR fluid and the strength of a magnetic field. The material of aluminum, brass, and steel are chosen for specimen as they are the most common material in mechanical applications. The surfaces of specimen are also observed by optical microscope before and after experiments to compare the surfaces with test conditions. The comparing results show that the friction coefficient increases as the strength of a magnetic field increases in regardless of types of MR fluid or the material. Also the density of particle in MR fluid affects the friction characteristic. The results from this research can be used to improve the performance of mechanical applications using MR fluid.

Jeffery-Hamel flow of non-Newtonian fluid with nonlinear viscosity and wall friction

A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.

Boundary layer flow and heat transfer of a micropolar fluid near the stagnation point on a stretching vertical surface with prescribed skin friction

The steady laminar mixed convection boundary layer flow and heat transfer of a micropolar fluid near the stagnation point on a stretched vertical surface with prescribed skin friction were considered.The governing partial differential equations were transformed into a system of ordinary differential equations,which were then solved numerically using the shooting method.Results for the stretching velocity,the local Nusselt number,the temperature,and the velocity profiles are presented for various values of the mixed convection parameter λ and material parameter K when the Prandtl number is equal to 1.Both assisting（heated plate） and opposing（cooled plate） flow regions are considered.It is found that dual solutions exist for both assisting and opposing flows.

Study on Quantitative Relationship between Surface Wettability and Frictional Coefficient of Liquid Flowing in a Turbulent Horizontal Pipe

This paper had investigated the effects of surface wettability on the frictional resistance of turbulent horizontal flow for tap water in five pipes made of various materials and four kinds of liquids in a polytetrafluoroethylene(PTFE) pipe,with the same inner diameter of 14 mm. Pressure drops were measured under different flow rates through an experimental flow loop. The contact angles and adhesion work of liquids in contact with pipe surfaces were determined using a contact angle meter. Based on the dimension and regression analyses, two kinds of modified relationships between the frictional coefficient and the surface wettability were established according to the measured results corresponding to tap water in five pipes and four liquids in PTFE pipe. The experimental results show that the surface wettability has some influence on frictional coefficient of the studied liquids flowing in macroscale pipes, and the frictional coefficient decreases with the increase of the contact angle at the same Reynolds number. Meanwhile the effect of wettability on the hydrophobic surface is greater than that on the hydrophilic one. The frictional coefficients predicted by the modified formulas have verified to be in good agreement with the experimental values, the relative errors of which are within ±6% and ±3% for the tap water flowing in five different pipes and four kinds of liquids flowing in PTFE pipe, respectively.

Fluid-solid Interaction Model for Hydraulic Reciprocating O-ring Seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.

Progress in Thermomechanical Analysis of Friction Stir Welding

This article reviews the status of thermomechanical analysis of the friction stir welding(FSW)process for establishing guidelines for further investigation,filling the available research gaps,and expanding FSW applications.Firstly,the advantages and applications of FSW process are introduced,and the significance and key issues for thermomechanical analysis in FSW are pointed out.Then,solid mechanic and fluid dynamic methods in modeling FSW process are described,and the key issues in modeling FSW are discussed.Di erent available mesh modeling techniques including the applications,benefits and shortcomings are explained.After that,at different subsections,the thermomechanical analysis in FSW of aluminum alloys and steels are examined and summarized in depth.Finally,the conclusions and summary are presented in order to investigate the lack of knowledge and the possibilities for future study of each method and each material.

径向油孔结构对环下润滑高速轴承内部流动特性的影响研究

为了研究径向油孔结构对环下润滑高速轴承内部流动特性的影响规律,根据高速轴承内部流动特征建立了数值计算方法,针对包含输油通道、径向油孔和轴承组件的物理仿真模型开展了油气两相流动计算,对比并讨论了不同径向油孔结构下轴承内部的油气分布和黏性摩擦损失。数值模拟结果表明,径向油孔孔径增大后轴承内部的平均滑油体积分数单调增加且滑油分布更均匀。径向油孔布设在周向油槽的同侧有利于提升轴承内部的平均滑油体积分数,同时滑油沿周向分布的均匀性较好。轴承组件表面扩展参数受径向油孔结构的影响,其变化趋势与平均滑油体积分数的变化相似。全部采用经验公式预测得到的黏性摩擦损失整体偏高,且不能反映径向油孔结构参数的影响,数值模拟和经验公式相结合计算得到的黏性摩擦损失与直接采用数值模拟获得的结果表现出较好的一致性。

HFC型液压元件摩擦副摩擦学性能研究

为了研究液压元件在HFC型水-乙二醇液压液下的摩擦学性能,采用MFT-5000摩擦磨损实验机考察不同载荷和滑动频率下,3种液压元件常用材料(304钢球、ZrO2和Si3N4)和304不锈钢配副的摩擦磨损变化情况,并借助白光三维干涉仪对304钢的磨痕进行形貌分析。结果表明:在水-乙二醇液压液的润滑作用下,滑动频率对摩擦因数的影响比载荷更大,载荷对磨损体积的影响比滑动频率更大;在载荷为50 N、滑动频率为3 Hz时,ZrO2和304钢配副的摩擦因数和磨损体积均为最小,磨损机制以三体磨粒磨损为主。综合考虑,ZrO2/304钢配副在不同载荷和滑动频率下摩擦因数和磨损体积更加稳定,更加适合作为HFC型液压元件的摩擦副材料。

深水气田长距离混输模式下水相运动规律研究

陵水25-1深水气田混输管道距离长、管道爬坡段坡度大,初始投产阶段混输流体水相到达平台的时间长且预测困难,给管道安全运行带来风险。基于多相流计算模型,运用LedaFlow软件,对陵水25-1深水气田初始投产阶段的水相运动规律进行研究,并深入分析含水率、油量、气量、油水相间摩擦系数等因素对水相运行的影响。结果表明:初始投产阶段水相在爬坡段分离和积聚,形成长时间的停滞,管道坡度越大,水相波动越剧烈;含水率越高的物流,水相在爬坡段聚集时间越短;气量增大则会降低水相滞液程度,提高水相运行速度,有助于水相爬坡;油量变化对水相运行速度的影响较小,油水相间摩擦系数对爬坡段水相运动有直接影响,油水相间摩擦系数修正拟合,对实际管道运行有重要指导意义。研究结果可为深水气田开发研究提供借鉴。

四主缆大跨悬索桥抗震性能分析及减震措施优化

以燕矶长江大桥为工程背景,首先,采用动力非线性时程法分析了燕矶长江大桥抗震性能,并研究了设置电涡流-摩擦组合型阻尼器和黏滞阻尼器对大跨悬索桥抗震性能的影响;然后,对附加电涡流-摩擦组合型阻尼器摩擦力、阻尼系数和阻尼指数开展了参数敏感性分析;最后,从耗能角度分析地震作用下电涡流-摩擦组合型阻尼器减震特点.结果表明:在E2地震作用下,桥塔关键截面抗弯能力均大于弯矩需求;在“纵向+竖向”地震作用下梁端纵向位移较大.设置塔梁处纵桥向阻尼器后,可有效降低主桥梁端纵向位移;增大摩擦力、阻尼系数与降低阻尼指数均可提升梁端纵向地震响应的控制效果,但参数变化对桥塔控制截面的地震响应影响较小.阻尼系数较大时,电涡流阻尼主导了电涡流-摩擦组合型阻尼器耗能,相较于黏滞阻尼器,电涡流-摩擦组合型阻尼器对梁端纵向位移控制效果更好.

Axisymmetric magnetohydrodynamic flow of micropolar fluid between unsteady stretching surfaces

This investigation examines the time dependent magnetohydrodynamic （MHD） flow problem of a micropolar fluid between two radially stretching sheets. Both strong and weak concentrations of microelements are taken into account. Suitable transformations are employed for the conversion of partial differential equations into ordinary differential equations. Solutions to the resulting problems are developed with a homotopy analysis method （HAM）. The angular velocity, skin friction coefficient, and wall couple stress coefficient are illustrated for various parameters.

纳米MoS_(2)固体薄膜制备及在钢领上的应用研究

为了减小纺织机械及器材专件的摩擦磨损,对比分析普通MoS_(2)油和脂与纳米MoS_(2)固体薄膜的润滑机理和特性,提出一种在钢领上采用真空化学气相沉积法合成纳米MoS_(2)固体薄膜的制备工艺;通过X射线衍射谱图和原子力显微镜,分析纳米MoS_(2)固体薄膜的组织结构及表面形貌,并对纳米MoS_(2)钢领进行镀铬镀氟渗杂复合膜处理。通过对比纳米MoS_(2)固体薄膜钢领与普通钢领纺纱质量,指出:纳米MoS_(2)固体薄膜具有优异的润滑性能,可以代替普通润滑油,达到纺织设备及器材专件少用油、不用油及无油自润滑的目的;纳米MoS_(2)的制备方法是制约其应用和发展的瓶颈;镀铬镀氟渗杂复合膜纳米MoS_(2)钢领在潮湿环境中不易生锈,较普通钢领的成纱质量好,值车工劳动强度小,钢领使用寿命延长。

抗高温油基钻井液的室内研究与应用

针对YJ3-X超深大斜度井三开井段存在的裂缝发育、井漏风险高、斜井段位移长、携砂困难、摩阻扭矩大、完井下套管作业时间长等钻完井难题,室内通过乳化剂的优选对现有抗高温油基钻井液体系配方进行了优化,并根据临井出现的复杂情况模拟该井可能出现的风险,评价了优化后钻井液体系的抗岩屑污染和盐水污染性能。试验结果表明,优化后的抗高温油基钻井液具有良好的流变性,抗温达180℃,破乳电压高达1366 V,高温高压滤失量低至2 mL,抗岩屑污染达20%,抗CaCl2盐水污染达30%,静置120 h后沉降因子为0.52,可满足井下各类复杂环境的作业需求。现场应用效果表明,优化后的抗高温油基钻井液流变性稳定,具有较低的黏度和较强的触变性,井眼清洁良好,起下钻和下套管摩阻低,井壁稳定,较好地满足了YJ区块大斜度深井作业需求。

列车制动作用下悬索桥纵向运动及其黏滞阻尼器控制研究

列车的制动行为会对悬索桥的纵向运动产生影响,因此有必要对千米级大跨度铁路悬索桥在列车制动下的纵向运动进行研究。以一座主跨1060 m的大跨度铁路悬索桥为研究对象,采用数值模拟的方式探讨了列车制动作用下其梁端纵向运动的响应特性,并研究了黏滞阻尼器在控制纵向运动中的效果。首先介绍了该千米级大跨径铁路悬索桥的工程背景,以及基于ANSYS软件建立的有限元模型;然后介绍了大跨径铁路悬索桥纵向运动的加载求解方式,支座摩阻和黏滞阻尼器的有限元模拟方式,以及制动力的模拟方式;接着探究了不同制动位置、是否考虑支座摩阻力对悬索桥梁端纵向运动响应的影响;最后,研究了黏滞阻尼器的纵向运动控制效果,并进行了参数分析。研究结果表明:随着制动位置越接近下桥位置,纵向位移变化曲线形状越接近正弦函数形式;支座摩阻对列车制动作用下的梁端位移响应有一定的控制作用,对梁端速度响应控制效果不佳;采用黏滞阻尼器可以有效控制列车制动下的悬索桥梁端位移和速度响应;当采用阻尼系数为2500 kN(m/s)^(-α),阻尼指数为0.1的黏滞阻尼器时,控制效果最佳。

两亲性碳点在硅酸盐钻井液中的润滑性能

硅酸盐钻井液具有抑制封堵能力强、环保等优点,但其润滑性能差,这制约了硅酸盐钻井液的广泛应用。利用极压润滑仪测定含有两亲性碳点和聚氧乙烯型表面活性剂的硅酸钠溶液的润滑系数,筛选出性能优异的润滑剂,并采用总有机碳分析仪、动态光散射和接触角仪等分析其润滑机理。实验结果发现,两亲性碳点具有优良的润滑性能和耐温性,在5%硅酸钠水溶液中添加0.3%两亲性碳点C_(12)-CDs,经过110℃高温热滚16 h前后体系的极压润滑系数可从0.500左右分别降低至0.065和0.063,润滑系数降低率高达87.52%,而聚氧乙烯型表面活性剂并无润滑效果。进一步探究其润滑机理,C_(12)-CDs在石英砂表面具有优异的吸附性能,100 mg/L的C_(12)-CDs溶液吸附前后的表面张力从44.81 mN/m上升为64.03 mN/m,其吸附量可达到89.23 mg/L;且粒径分析数据表明,C_(12)-CDs可将Na_(2)SiO_(3)溶液的平均粒径从514.0 nm分散为63.2 nm。碳核表面的多羟基结构和长疏水链可促进两亲性碳点在金属钻杆、井壁和硅酸聚集体表面的吸附,两亲性碳点作为润滑剂与硅酸钠钻井液体系配伍性能好,添加C_(12)-CDs的现场硅酸盐钻井液润滑系数降低率可达到86.34%,可为硅酸盐水基钻井液润滑剂的现场应用提供理论指导。

含摩擦界面复合材料输流管道非线性振动分析

针对含摩擦界面复合材料输流管道流固耦合动力学问题,基于Reissner薄壳理论和对流波动方程建立了纤维增强复合材料管道和流体介质的动力学方程,采用宏观滑移摩擦模型刻画管道摩擦界面上的非线性摩擦力分布,发展轴对称半解析有限元方法来构建含摩擦界面复合材料输流管道非线性动力学模型,研究了流体载荷和摩擦界面等对管道非线性振动响应的影响.结果表明,含摩擦界面复合材料输流管道摩擦界面上点的滞回曲线由两个对称的黏滞区域和两个对称的滑移区域组成,摩擦界面的黏滞-滑移切换导致输流管道振动响应除包含激励频率外,还包含一系列奇次超谐波;随着界面摩擦系数增大,输流管道基频处的轴向振幅减小,法向振幅增大,而3次超谐波处的轴向及法向振幅先增大后减小;随着界面摩擦刚度增大,输流管道基频及3次超谐波处的轴向振幅先减小后增大;来流速度主要影响含摩擦界面输流管道的法向振动,对管道的轴向振动影响很小.

一种钻井液润滑剂的制备及其性能评价

基于现有钻井液润滑剂吸附、润滑抗磨性能差的问题,本文以多元醇、多元羧酸为原料制备一种强吸附、抗剪切的润滑剂(HR-1),采用极压润滑仪和四球摩擦试验机评价其润滑抗磨性能,并通过扫描电镜&能谱仪对其润滑机理进行探讨。实验发现,润滑剂HR-1显著提高了膨润土基浆的润滑抗磨性能,优于现场应用效果较好的润滑剂BLOE;另外,润滑剂HR-1使钢球表面的C元素含量升高以及Na、O元素含量降低,这表明,润滑剂HR-1的加入使润滑剂分子取代了原本吸附在钢球表面的钠基膨润土,且降低了摩擦腐蚀产物(Fe_(3)O_(4))的形成,起到润滑抗磨作用,达到保护金属的目的。

基于流固热多场耦合的高速旋转唇形密封性能研究

针对一种橡胶材料高速旋转唇形密封,结合其自身结构及应用工况,通过方程离散化计算等方法,建立定量分析密封系统密封性能的数值仿真模型。基于所建立的模型对密封实际服役状态下界面流体力学、宏观固体力学、表面粗糙峰微观接触力学、唇口摩擦生热等多物理过程之间的耦合关系进行分析,借助实验验证并完善数值仿真模型的准确性。通过所建立的数值仿真分析模型研究油封唇口接触压力分布、唇口温度、摩擦力矩及泄漏率等衡量密封性能的关键参数随转速的变化规律。结果表明:在高转速条件下考虑摩擦生热时油封径向力减小,接触宽度增加,摩擦力矩减小,说明摩擦热对油封密封性能产生较大影响。

3D打印铸造铝合金表面楔形织构的摩擦性能

实验对活塞-缸套使用较多材料铸造铝合金(AlSi10Mg)进行3D打印,研究其摩擦磨损性能。在内燃机实际运行条件下活塞裙部通常会发生严重的摩擦和磨损。表面织构已成为现代减摩抗磨的有效方式之一,并成功应用于许多领域。利用3D打印技术加工出两种不同面积占有率楔形凹坑表面试样与光滑表面试样。在立式万能摩擦磨损试验机上进行销-盘回转实验,采用三维形貌仪、同轴显微镜以及扫描电子显微镜观察试样工作表面的磨损形貌。通过Fluent流体分析软件模拟仿真润滑油内部压力,并对仿真结果进行验证。研究结果表明,与光滑无织构试样对比,楔形织构试样对提升活塞裙部摩擦学性能起着积极的作用,且当织构面积占有率为7.01%时对减少摩擦系数降低磨损质量的效果更加显著,提升了活塞裙部的摩擦学性能。