工程车辆发动机润滑系统的常见故障诊排

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

上海帕萨特轿车发动机的故障诊修8例

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

气门冲击淬火调高阳压温度不升原因分析

内冷油腔强制冷却是降低高强化柴油机活塞热负荷的有效方法,但内冷油腔冷却对冷却喷嘴及喷油有着较高的要求,本文通过介绍流体特性及内冷油腔活塞对喷油冷却的要求,简要阐述了冷却喷嘴设计注意事项及冷却喷嘴喷油试验情况。     

非极性流体在微通道内的阻力特性分析

研究非极性流体在微通道内的流动特性。采用的微流动实验台通过测量不同极性液体流过矩形截面微通道中流量与压力,分析了不同极性流体的阻力特性。结果表明:对分子量较小的极性液体,微通道内流量-压差关系符合Hagen-Poiseuille定律,连续介质模型仍适用于微米尺度微通道;对分子量较大的非极性液体,常规理论在预测微通道内流量-压差、摩擦阻力系数-雷诺数关系时存在较大误差,须进行修正。     

基于格子Boltzmann方法的分叉微通道内非牛顿流体流动特性研究

为探究分叉微通道内非牛顿流体的流动特性,将非牛顿流体幂律模型引入牛顿流体格子Boltzmann模型,在不同分叉角度矩形截面微通道内数值模拟不同质量分数剪切稀化流体的流动行为;通过分析流动过程中密度随时间的变化趋势以及稳态流动下的密度,得到微通道内压力的分布以及流动区间的压力降;分析溶液质量分数、入口速度与分叉角度对非牛...     

矩形带肋通道中脉动流强化换热数值研究

为了提高燃气轮机叶片内部对流冷却,采用脉动蒸汽流取代稳态蒸汽流作为内冷介质。利用数值计算方法研究脉动蒸汽流在矩形带肋通道中的强化换热能力。通过与稳态蒸汽流的对比,分析了非稳态脉动流的脉动频率、脉动幅值和雷诺数对换热效果的影响。计算结果表明,脉动流对换热的影响取决于流体压力梯度的大小,当脉动的蒸汽处于逆压梯度区间,逆压梯度越大瞬态换热更强。而顺压梯度有稳定流体的作用,在顺压梯度时间区间,有瞬时的换热甚至低于稳态流体冷却的情况出现。     

离散叉排肋化内冷通道流动与传热的数值模拟

运用数值模拟方法,计算肋片导流角θ为15°～45°的离散叉排肋化冷却通道在雷诺数介于1×104～20×104之间时的换热和流阻特性。研究结果表明,(1)各算例的强化换热能力随雷诺数的增大而减小,流动阻力随雷诺数的增大而增大,综合换热效率随雷诺数的增大而减小。(2)肋片导流角的改变可以显著改变通道的换热和流阻特性。相同雷诺数下,θ=45°的强化换热比和通道阻力增大比最高,θ=15°的强化换热比和通道阻力增大比最低。在研究范围内θ=15°的综合换热效率最好。     

静电微泵的3D流固耦合动态特性分析

采用任意拉格朗日—欧拉(ALE)描述建立了无阀微泵的静电-结构-流体全耦合三维模型,数值仿真表明:泵内流体的动态特性与泵膜的运动存在着密切的关系;扩散/收缩口单元两端的压力差必须达到一定值后才有"整流"泵送效用;泵腔内流体压力的分布几乎一致;流体流动的最大雷诺数远小于宏观条件下认定的临界雷诺数;流体黏滞损失的非线性不容忽视。     

梯形带肋通道内空气流动与换热特性数值研究

带肋扰流冷却是航空发动机涡轮叶片内部冷却的一种主要冷却方式。采用CFX等计算流体动力学软件,通过气热耦合数值模拟方法,对比分析了梯形冷却通道和矩形冷却通道内空气的流动和换热特性,研究了雷诺数(Re=10 000~30 000)和肋角度(30°、45°、60°和90°)对梯形带肋通道内空气流动及换热特性的影响。     

超临界CO_2微细管内传热特性研究

考察超临界CO2微细管内冷却条件下流动和换热的细观信息(管内不同截面湍动能分布,无量纲速度和温度分布以及湍流雷诺数分布等),结果表明:近壁处湍动能的变化对传热有较大影响,微细管内换热关联式需考虑浮升力的影响。对管径d=0.5,0.3,0.1 mm时,超临界CO2的换热特性进行计算分析,回归出管径小于0.5 mm时,超临界CO2在冷却条件下竖直向上流动和竖直向下流动时的换热关联式,作为对超临界CO2研究的有效补充。     

单回路闭式脉动热管内流型的实验研究

对一个单回路闭式脉动热管进行了实验研究.该热管由铜管及玻璃管(内直径均为2mm)合制而成.两端的U形弯头是由细铜管弯曲而成,一端通电加热,另一端通水冷却.中间为两根直的平行玻璃管,采用酒精为工质.本实验目的是,揭示脉动热管内部所存在的复杂的气液两相现象,更好地理解其运行特性.实验表明流型及重力等对单回路系统的热力性能有着重要的影响.     

Numerical simulation of flows of non-Newtonian fluids in the stenotic and bifurcated tubes

Steady flows of Newtonian and non-Newtonian fluids in the stenotic and bifurcated tubes are numerically simulated. Four rheologically different fluids such as water, aqueous sugar solution, aqueous Carbopol solution and blood are selected for the namerical simulation and the modified power-law model is used for the numerical simulation of non-Newtonian fluids in the stenotic and bifurcated tubes. Apparent viscosity of a non-Newtonian fluid in the modified power-law model is expressed as a function of the shear rate. Flows in the circular tube with sudden contraction-sudden expansion and gradual contraction-gradual expansion are studied numerically. Analyses in the stenotic tubes are concentrated on the effects of rheological properties, the stenotic geometry and Reynolds number. Flow characteristics of Carbopol solution in the stenotic tubes are compared with those of blood. Effects of the bifurcation geometry on the flow behaviors of Newtonian and non-Newtonian fluids are numerically investigated. Numerical analyses are focused on the flow patterns in the branch tubes of which angles are 30°, 60° and 90° and on the diameter ratios for Newtonian and non-Newtonian fluids. Variations of the axial velocity and pressure drop along the bifurcated tubes for various flow parameters are presented for Newtonian and non-Newtonian fluids.     

凸轮转子泵抽送不同浓度非牛顿流体的流场分析及对性能影响

为了探讨摆线型凸轮转子泵抽送粪污介质的性能变化和针对非牛顿流体类抽送的优化设计,以三叶摆线型凸轮转子泵作为研究对象,选取清水和浓度为6.87%,9.20%,12.15%的猪粪作为抽送介质,对凸轮转子泵进行三维非定常数值模拟,分析内部流场瞬态特性,预测其外特性。分析结果表明:在抽送清水和不同浓度的猪粪时,从泵腔的进口区域到出口区域的压力逐渐升高,随猪粪浓度增大,独立工作腔室的压力增大;抽送非牛顿流体时,间隙处因挤压而产生的速度激增,转子泵腔内的速度分布更加均匀;出口的压力脉动主频均出现在2倍叶频处,压力脉动幅值随猪粪浓度增大而减小;随猪粪浓度增大,出口流量、容积效率及水力效率增大,流量脉动系数减小,其性能优于抽送清水介质。研究为凸轮转子泵输送非牛顿流体时的优化设计奠定了基础。     

脉动热管理论及技术进展

脉动热管作为热管家族新成员,相对传统热管和其他的散热器件有着很大的传热优势,能够实现高热流密度的微型电子器件的散热要求,近年来很多学者开展了对脉动热管的理论和技术研究,本文主要从以下方面介绍脉动热管研究进展:实验研究,通过可视化和传热性能实验,观察流型变化并分析传热强化效果;理论研究,通过建立脉动热管的简化模型,采用数值模拟的方法观察流动过程中流态的变化或者采用数值编程计算的方法分析求解脉动热管的传热过程;管路结构改进研究,采用不同的脉动热管的管路形式来实现两相流工质的合理分配,减少两相流的局部阻力,从而分析其对传热的影响。     

The consistency of pressure effects between three identical Coriolis flow meters

Coriolis flow meters are one of the most popular flow measurement technologies in the world today for high accuracy measurement of single-phase liquids, gases and even slurries. They are capable of measuring both mass and density directly and can also infer the volume flow. They can be installed in challenging process environments and have been successfully deployed with non-Newtonian fluids, high viscosity fluids, pulsating flows and even at extreme temperatures and pressures.However, it is known that operating most Coriolis flow meters at a pressure which differs from the original calibration pressure requires compensation else significant measurement errors will occur. Pressure compensation coefficients appear to vary by manufacturer, meter geometry and sensor material. Furthermore, the manufacturer published pressure compensation coefficients are not fully traceable. To date, there has not been sufficient research exploring the consistency of the pressure compensation for identical Coriolis flow meters.This paper presents the findings of a research conducted at the TÜV SÜD National Engineering Laboratory (NEL) Elevated Pressure and Temperature (EPAT) oil flow facility to investigate the pressure effect uniformity for matching Coriolis devices. The first stage of the experimental programme calibrated three identical DN80 Coriolis flow meters at a range of pressures with no pressure compensation applied. A pressure compensation coefficient was then derived from the data and the Coriolis meters were then calibrated at two alternative pressures to ascertain the robustness of the coefficients and whether the compensation could be extrapolated successfully.From the experimental results, it can be concluded that the pressure effect for the three DN80 Coriolis flow meters was extremely repeatable and consistent with a discrepancy of less than 0.025% between the devices at 80 bar. Whilst the mass flow was significantly affected by fluid pressure, the fluid density did not appear to be influenced. The pressure corrected results were also well within the manufacturer specification of ±0.1%.     

Thermo-hydrodynamics of closed loop pulsating heat pipe: an experimental study

The experimental result on the thermal performance of closed loop pulsating heat pipe (CLPHP) is presented. The CLPHP is made of copper capillary tubes, having inner and outer diameters of 2.0 mm and 3.6 mm respectively. The working fluids employed are water, ethanol, methanol and acetone also binary mixture (1:1 by volume) of water-ethanol, water-methanol and water-acetone. For all experimentations, filling ratio (FR) 50%, two-turns and vertical bottom heat mode position was maintained. The lengths of evaporator, condenser and adiabatic section are selected as 42 mm, 50 mm and 170 mm, respectively. The transparent adiabatic section is partially made of glass tube having length 80 mm, for flow visualization. The CFD analysis by VOF model in Star CCM+ simulation is carried out to validate the experimental results. The result shows that the thermal resistance decreases smoothly up to 40W heat input, thereafter reasonably steady. In comparison with all working fluids, water-acetone binary working fluid has shown the best thermal performance over other working fluids used in CLPHPs.     

Numerical simulation of fully developed flow and heat transfer characteristics in a curved tube with pulsating pressure gradient

Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.     

轴承腔中均匀流体/壁面油膜分层流动分析

航空发动机轴承腔精确的润滑与换热设计依赖于对其内油气两相润滑介质流动与换热本质的认识。针对轴承腔内复杂的油气两相润滑介质流动状态,建立轴承腔均匀流体/壁面油膜分层流动分析模型,开展腔内油气两相润滑介质流动特性研究,探讨转子转速和润滑油供油量对均匀流体和壁面油膜两相介质压力、速度以及温度分布的影响。分析模型中,气相介质(含油滴)的等效物理特征参数通过离散油滴和气相介质的组分比例关系确定,各固体壁面与流体介质的对流换热系数根据其各自的传热特性确定。研究结果表明,均匀流体与壁面油膜两相介质的压力随着润滑油供油量的增加而增大,受转子转速的影响较为复杂;均匀流体与壁面油膜两相介质的速度随着转子转速的增高而增大,受润滑油供油量影响较小;均匀流体的温度随着润滑油供油量的增加而减小,受转子转速的影响较小;与均匀流体温度不同,壁面油膜的温度随着转子转速的增加而增大,随着润滑油供油量的增加而减小。建立了轴承腔试验台系统,开展了轴承腔油气两相流动状态下的压力和温度测试,压力和温度试验结果与理论计算结果均具有较好的吻合性,验证了提出的理论分析方法的可靠性。     

Rheology of synthetic lubricating oils

A lubricating fluid's flow characteristics are affected by fluid deformation resulting from the action of mechanical forces: flow resistance, dissipation of mechanical energy, transfer and dampening of mechanical disturbances. These in turn affect the lubricating ability of the fluid through energy absorption, power transfer and other properties. Synthetic fluids can display various thixotropic characteristics and non-Newtonian effects. In this paper, experimental work on these phenomena are reported.