Kinetic model of mutual effect of the components on the viscosity of binary mixtures

A kinetic model describing the temperature dependence of the viscous flow of multicomponent liquids over the whole range of compositions is suggested. It takes into account the mutual influence of component molecules—either increasing or decreasing the activation energy of viscous jump of each other, which formally is equivalent to catalysis. The quantitative possibilities of the model are shown using liquid binary systems characterized by strong intermolecular interactions.     

高粘性液体试剂的自动化微量分配系统

在膜蛋白结晶等生物工程领域,常需要对高粘性生物试剂进行精确的分配和转移操作.研制一套液体操作机器人系统,它可以实现纳升级别高粘性试剂的精确分配操作.介绍该系统的结构原理,主要由运动控制模块、分配控制模块和液滴体积检测模块等组成,分别用来实现液滴的精确分配操作和体积检测功能.接下来对影响试剂分配过程的因素进行分析,给出成功实现微量试剂液滴分配操作时,分配头与基板之间高度必须满足的临界高度范围.针对具有不同粘度的三种试剂进行分配试验,验证理论分析结果,结果表明该系统分配精度小于7%,重复精度(用变异系数表示)小于10%.     

空化效应对斜线槽机械密封性能的影响

润滑膜的空化效应对流体动压型机械密封的密封性能影响显著。以煤油基磁流体润滑斜线槽上游泵送机械密封为研究对象,考虑空化热效应以及黏温效应,建立润滑液膜特性的数值分析模型,以液膜中的气相体积分数为指标,研究工况和结构参数对密封性能的影响规律,并与仅考虑黏温效应的模型进行对比。结果表明：因空化热模型考虑液膜介质饱和蒸汽压力随温度变化,考虑空化热效应时的开启力、泄漏率和气相体积分数均小于仅考虑黏温效应下的对应值,但2种条件下各参数的变化趋势基本一致;转速和槽径比增大,空化效应增强,而进口压力、膜厚、径向夹角和槽数的增大会削弱空化效应;转速、槽深、径向夹角、槽径比增加,会导致泄漏率增加,而进口压力和槽数的增加能够提升密封性能。     

Cryo-SEM specimen preparation under controlled temperature and concentration conditions

Cryogenic temperature scanning electron microscopy (cryo-SEM) is an excellent technique for imaging liquid and semi-liquid materials of high vapour pressure, which are highly viscous or contain large (>0.5 μm) aggregates, in which nanometric details are to be studied. However, so far there have been no adequate tools for controlled cryo-specimen preparation. The specimen preparation stage is critical, because most of those samples are very sensitive to concentration and temperature changes, leading to nanostructural artefacts in the specimens. We designed and built a system for easy and reliable cryo-SEM specimen preparation under controlled conditions of fixed temperature and humidity. We describe this new methodology, and demonstrate its applicability, by showing imaging data of three liquid material systems. We have studied carbon nanotubes (CNTs) dispersions in superacid. We also characterized a number of systems made of water/isooctane/nonionic and cationic surfactant that showed different microemulsion phases as function of the system composition and temperature. In all of the examples given, we demonstrate artefact- and contamination-free specimens, which have preserved their native nanostructure. Our new system paves the way for a new methodology for the newly emerging field of cryo-SEM.     

Thermorheological behaviour of a lithium lubricating grease

Thermal-induced changes in the viscous and viscoelastic responses of lubricating greases have been investigated through different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear and viscous flow measurements were carried out on a model conventional lithium lubricating grease prepared by inducing the in situ saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide. The linear viscoelasticity functions dramatically decrease above 110 °C, but not below this critical temperature, which determines the maximum recommended operating temperature in relation to its durability and resistance under working conditions. Two different regions, below and above this critical temperature, in the plateau modulus versus temperature plot have been detected. From this thermal dependence, a much larger thermal susceptibility of the lubricating grease at temperatures above 110 °C is apparent. The thermo-mechanical reversibility of this material has been studied by applying different combined stress–temperature protocols. Regarding the viscous flow, a minimum in the shear stress versus shear rate plots appeared at temperatures above 60 °C, more pronounced as temperature increases, resulting from material instabilities. The experimental results obtained have been explained on the basis of the thermo-mechanical degradation of the lubricating grease microstructure.     

Experiment and simulation study on cavitation flow in pressure relief valve at different hydraulic oil temperatures

Hydraulic oil is the “blood” of hydraulic system, its high temperature in low-pressure hydraulic system would promote the development of cavitation and cause severe erosion of pressure relief valve. The influence of high oil temperature on the distribution of pressure field, velocity field and vapor volume fraction are discussed experimentally and numerically. The results show that with the increasing oil temperature, the viscosity of the oil decreases, and the flow rate increases, resulting the decreasing pressure at the orifice. Higher oil temperature promotes the occurrence of cavitation in the pressure relief valve, wider low-pressure zone could be found and cavitation bubble developed more fully and towards the valve core head. When the oil temperature increases from 303 K to 353 K, the cavitation intensity rises more sharply, but the growth rate of cavitation intensity increases firstly and then decreases with the increasing input pressure. Furthermore, based on the field synergy theory, the flow resistance and energy dissipation under different oil temperatures are evaluated. Both of large viscous dissipation and effective viscosity coefficient are mainly concentrated at the orifice, which are all effected by the oil temperature, so as to the characteristics of cavitation flow. The average field synergy cosine angle and the average viscosity coefficient decreases gradually with the increasing oil temperature, while the average vapor volume fraction increases. The energy dissipation is reduced by 3.3 × 10⁷ (W m⁻³) while the hydraulic oil temperature increases from 303 K to 353 K. Appropriate hydraulic oil temperature could provide favourable working conditions for the pressure relief valve which is beneficial for extending the hydraulic system's service life.     

Four degree of freedom liquid dispenser for direct write capillary self-assembly with sub-nanoliter precision

Capillary forces provide a ubiquitous means of organizing micro- and nanoscale structures on substrates. In order to investigate the mechanism of capillary self-assembly and to fabricate complex ordered structures, precise control of the meniscus shape is needed. We present a precision instrument that enables deposition of liquid droplets spanning from 2 nl to 300 μl, in concert with mechanical manipulation of the liquid-substrate interface with four degrees of freedom. The substrate has sub-100 nm positioning resolution in three axes of translation, and its temperature is controlled using thermoelectric modules. The capillary tip can rotate about the vertical axis while simultaneously dispensing liquid onto the substrate. Liquid is displaced using a custom bidirectional diaphragm pump, in which an elastic membrane is hydraulically actuated by a stainless steel syringe. The syringe is driven by a piezoelectric actuator, enabling nanoliter volume and rate control. A quantitative model of the liquid dispenser is verified experimentally, and suggests that compressibility in the hydraulic line deamplifies the syringe stroke, enabling sub-nanoliter resolution control of liquid displacement at the capillary tip. We use this system to contact-print water and oil droplets by mechanical manipulation of a liquid bridge between the capillary and the substrate. Finally, we study the effect of droplet volume and substrate temperature on the evaporative self-assembly of monodisperse polymer microspheres from sessile droplets, and demonstrate the formation of 3D chiral assemblies of micro-rods by rotation of the capillary tip during evaporative assembly.     

Fiberglas insert to liquid helium Dewar

We present the design of a simple Fiberglas insert to the liquid helium space of a conventional metal Dewar that results in a considerable reduction in the liquid helium evaporation rate. The original purpose of this simple modification was to minimize the volume of liquid helium that is used for experiments not requiring the full volume available at low temperature.     

Vorticity and viscous dissipation in an incompressible flow

The relation between the vorticity and viscous dissipation in an incompressible flow has been investigated. It is shown that the square of relative vorticity with respect to the coordinate system fixed to the container or to the flow at infinity gives the global rate of viscous dissipation, that is, the viscous dissipation is proportional to the volume integral of the square of relative vorticity. Thus, the total rate of viscous dissipation in the flow produced by the motion of a rigid body is proportional to the integral of the square of vorticity taken over the whole space including the region occupied by the volume of the rigid body in which the vorticity is assumed to be the twice of the angular velocity of the body.     

储罐中的超稠油液位检测设计与实现

超稠油介质具有独特的物性,常温下的粘度极高,其生产过程需要在较高温度下进行操作运行。由于操作运行温度较高,且超稠油的密度与水接近,在液位测量方面需要针对实际,采取可靠、实用的测量方法。此方法的介质液位检测通常有微波法、射线法、射频导纳型、差压式等。     

468Q汽油机润滑系统循环油量的计算及试验研究

按照经验公式估算了自行开发的468Q汽油机润滑系统的循环油量,行车试验发现,汽油机由高速大负荷运行突然转为怠速运行时,在怠速偏低和苛刻行驶后机油温度偏高的共同作用下,使用较低黏度等级的机油出现了油压偏低、油压报警的问题。针对这一问题提出了一种以发动机在热车状态低速运转时所需保证的最低机油压力为条件,依据流体力学基本原理的润滑系统循环油量的计算方法,根据计算结果重新调整机油泵的循环油量,试验结果表明机油压力满足汽油机的工作要求。     

Viscous pressure bulging of aluminium alloy sheet at warm temperatures

Improving the formability of aluminium alloy sheet metal by using warm or elevated temperature has become a valid approach. In this paper, viscous pressure bulging (VPB) at warm temperature is proposed. The coupled thermo-mechanical finite element method and experimental method were used to investigate the VPB of aluminium alloy AA3003 at warm temperature. The temperature distributions of sheet metal and viscous medium were analyzed for non-isothermal VPB. The influence of forming temperature on thickness distribution, forming load and failure location of sheet metal were investigated. Research results show the temperature gradient field in sheet metal forms when the initial temperature of viscous medium is lower than that of sheet metal. The formability and failure location of sheet metal changes with initial temperature of viscous medium.     

不同燃油温度下柴油机喷嘴空穴流动特性试验研究

作为喷射系统的终端,喷油器内部的空穴流动对燃油雾化具有重要影响。采用比例放大透明喷嘴,研究不同燃油温度对喷嘴内空穴流动及其对近场喷雾的影响。引入无单位参数空穴数表征喷油器内燃油空化程度,研究发现燃油温度升高,其空穴初生时的压力减小,同一空穴数下,空穴程度更强烈。同时,试验观察到喷嘴内空穴区域的不对称性,喷孔管壁下壁面的空穴分布远大于上壁面的空穴分布;发生超空穴之后,随着空穴数的增加,试验结果中喷嘴内部的空穴流动变化不太明显,但仿真结果中看出喷孔出口流速减小。相同燃油温度下,随着空穴数增加,体积流量增加,流量系数减小,空穴相对面积增加,近场喷雾锥角增大;相同空穴数下,燃油温度增加使体积流量和流量系数都增加,空穴相对面积逐渐增大,近场雾化效果更好。     

基于转速转矩双闭环的液黏调速控制方法研究

液黏风扇调速系统存在滞环、死区、饱和区等多种非线性特性,在调速过程中,其输入输出关系曲线存在最大可达44%的滞环和大约为43%的死区,非线性度最大可达30%。设计了转速-转矩双闭环模糊控制策略:结合Stribeck摩擦理论,按照稳态曲线的分段线性规律将控制过程分段,获得模糊控制表;基于扩展卡尔曼滤波环节修正转矩测量值,从主动轴与从动轴之间的转矩传递关系分析输出转速变化规律,并进行试验验证。结果表明:相比于PID控制策略,所提出的控制策略将转速误差降低了75%,滞环减小至小于11%,消除死区,拓宽控制电压输入范围,有效改善了系统稳态调速过程中表现出的非线性滞环和死区现象。     

火箭增压输送系统减压阀出口压力性能改进研究

为解决液体火箭增压输送系统气体减压阀在生产和飞行试验中出现的出口压力长时间持续下降问题,基于实测摩擦力提出了O形圈黏弹摩擦特性对减压阀出口压力的影响机理。使用修正摩擦力后的减压阀仿真模型复现了该减压阀出口压力长时间持续下降现象,并提出改进方案。样机验证试验表明,改进后减压阀出口压力长时间下降现象明显改善,减压阀精度提高约30%,验证了改进方案的有效性和O形圈黏弹摩擦特性对减压阀出口压力影响机理的正确性。     

Study on Changes in the Rheologic Properties of EHL Film Using Fluorescence Measurements

This article describes a fundamental study using the fluorescence measurement method to understand the rheologic properties (such as viscosity and solidification) of elasto-hydrodynamic lubrication (EHL) film. The measurement principle is based upon the excimer emission of a pyrene fluorescence agent, which depends on the viscosity. To investigate the relationship between the excimer emission and viscosity, the measurements were taken under low temperature, with the results showing that the excimer emission decreased with decreasing temperature because of increasing of viscosity. No remarkable peak was observed below the temperature at which the state changed from liquid into a viscoelastic or elastic–plastic solid. The fluorescence was clearly observed in EHL film, and its spectrum revealed that the intensity of excimer emission decreases along the flow direction, with a contact area having the same behavior as that of the elastic–plastic solid at 243 K. These results suggest that the viscosity increased at the inlet of contact because of increasing hydrodynamic pressure under the wedge action and that the state in the contact region changes to solid because of high contact pressure. This study also proposes that this measurement method can be used to understand the viscosity change and solidification in the lubrication film.     

液粘调速器的结构和理论分析

液粘调速器是利用摩擦片间的相对滑动来实现无级变速的新型传动装置。由于它的动力传递，转矩改变和转速的调节都是靠液体的粘性来实现的，所以这种传动实质上就是液体的粘性传动。本文将重点阐述这种传动的结构和油膜传动机理。     

超声外场对微通道中熔体黏性耗散效应的影响

针对聚合物熔体在微尺度通道中流动时的黏性耗散效应对其流动行为的影响,通过自行构建的带有温度传感器和超声振子的微注塑成型试验系统,采用单因素成型试验方法,对聚丙烯(Polypropylene, PP)和高密度聚乙烯(High-density polyethylene, HDPE)两种聚合物材料在不同工艺参数和超声外场作用下,流经矩形截面微通道时由黏性耗散效应引起的通道出口熔体温升进行试验测量。结果表明,微通道中熔体的黏性耗散效应随注射速度的增加而增强,随入口熔体温度和模具温度的升高而减弱;与不加超声振动相比,施加超声振动使两种材料的微通道出口熔体温升值明显升高;但材料自身的微观分子结构及其热物理性能不同,其温升增幅差别较大。试验注射速度下,施加超声振动比不加超声振动时的PP熔体温升增幅高出34.7%,而HDPE熔体的温升增幅则高达71.7%。当超声频率和工艺参数一定时,增大超声功率使PP熔体的微通道出口温升增加了24.8%,HDPE熔体的温升增加了83.6%。可见施加超声外场作用能使微通道中聚合物熔体的黏性耗散效应明显增强。     

液黏传动摩擦副流固耦合传热分析

为探求液黏传动在充满工作油的流体阶段摩擦副温度分布情况,建立薄盘结构摩擦副热流固耦合模型,采用计算机流体仿真软件FLUENT对径向槽摩擦副进行数值模拟,得到摩擦副的温度云图。通过搭建液黏传动装置试验台,测得径向油槽摩擦副间油膜温度分布数据。结果表明:在径向方向上,随半径的增加,摩擦副温度逐渐增加且沟槽处温度低于无沟槽处;在圆周方向上,相同半径处摩擦副的沟槽区比无沟槽区温度高,表明沟槽可以有效地降低工作油的升温;在纯油膜阶段摩擦片升温明显高于对偶片升温。有限元分析和实验研究结果趋势基本一致,验证了理论分析的可靠性。     

Process control of product quality

This paper describes a method to control output product quality (product variability) by applying engineering or automatic process control (APC) and statistical process control (SPC) techniques. APC techniques have been used to control process variables such as feed rate, temperature, pressure, viscosity, and to product quality variables as well. SPC techniques have also been applied to control product quality. APC and SPC techniques overlap at the interface of the two process control methodologies. It is possible to produce material of desired quality by having an acceptable level of variation in the measured output characteristics. APC aims to maintain certain key process variables as near their set points for as much of the time as possible. There are situations in process control where some form of feedback control is necessary and yet where stability cannot be easily attained in the feedback control loop. Disturbance (noise) afflicts a process, which together with issues of dynamics and dead time (time delay) compounds the process control problem. The process control practitioner faces a challenge while tackling issues of process delay (dead time) and dynamics (inertia). Process control of product variability (control error standard deviation) is possible by developing and simulating a feedback control algorithm for dead-time processes. It is quite common to encounter problems connected with feedback (closed-loop) control stability, controller limitations, and dead-time compensation to obtain minimum variance (mean square error) control at the output. Details of a method to control the quality of a product at output by applying statistical process monitoring and feedback control adjustment are presented in this paper. The focus of this paper is on the issues of process delay ("dead time") and dynamics ("inertia") at the interface between SPC and APC to control output product quality.