磁流体在磁场中的粘度测试研究

针对磁流体在磁场中粘度测试的特殊性,研制了一种新型的旋转法磁流体粘度测试实验台,该实验台可通过测试带动工作气隙内磁流体作旋转剪切运动所需的力矩来推算得出磁流体的粘度,满足磁流体在磁场中的粘度测试要求。利用所设计的实验台对矿物油基Fe3O4磁流体的粘度进行了测试,研究了外加磁场、温度及磁流体中磁性颗粒含量对其粘度的影响规律。结果表明:磁流体的粘度随着外加磁场强度的增加而增大,当磁场强度增大到一定程度时,其粘度变化逐渐趋缓;随着温度的升高,磁流体的粘度呈不断下降趋势,在有外加磁场作用情况下,其粘度下降的幅度要远大于无外加磁场作用的情况;随着磁流体中所含磁性颗粒质量分数的增加,其粘度逐渐增大,当磁性颗粒质量分数小于30%时,粘度增加缓慢,但当质量分数超过30%以后,粘度则急剧增大。     

磁场作用下磁流体粘度特性的研究

采用自制的试验设备研究了磁流体的粘度与外加磁场及温度的关系。结果表明：磁流体的粘度随温度的增加而减小;当环境温度一定时,在磁场的作用下磁流体的粘度会增加,粘度的大小与磁场作用的时间有关;磁场作用达到一定时间后,磁流体的粘度达到稳定;随着磁场的增加,磁流体的粘度增加,当磁场达到一定强度后粘度不再增加。     

滑动轴承磁流体薄膜和润滑特性的研究

在横向外磁场作用下，同时伴随磁流体中磁粒子的转动时，推导磁流体薄膜中压力的雷诺方程表达式；研究不同载体类型的磁流体在外磁场作用下，对无限长挤压薄膜轴承和滑动轴承的润滑特性的影响。结果表明：磁场增加磁流体液膜的粘度，提高薄膜承载力，而对轴承的滑动摩擦力影响很小。     

船舶艉轴磁流体密封液的制备与性能研究

针对船舶艉轴的密封问题,采用化学法制备了以Fe3O4为磁性粒子,以水、油和氟醚油为基液的磁流体密封液,并分别对其疏水性能、疏油性能进行了研究,分析了磁化特性、粘度特性和悬浮稳定性的影响因素.结果表明:磁流体的磁化强度随着外加磁场强度的增大而增大,粘度随着密度的增大而增大;在外加磁场作用下,水基型磁流体表现出极强的亲水性和亲油性,而油基型磁流体具有较好的疏水性和疏油性,密封能力较好.     

磁流体轴承的磁场与润滑特性分析研究

针对电机轴承高速化载荷高的需求以及磁流体轴承具有的自润滑密封、可靠性高、高速、低摩擦润滑等一系列优点,对磁流体轴承在不同条件下的性能开展了研究。首先从理论上推导了磁流体粘度的相关公式,通过采用Matlab软件在外加磁场的条件下,对磁流体的粘度进行了修正,并给出了磁流体轴承润滑的粘温、粘压特性。其次,采用有限元分析方法设计了外加磁场,并对轴承内部的磁场分布进行了分析。研究结果表明,在外加磁场的作用下,磁流体轴承润滑的粘度发生变化,同时,相较于传统普通轴承,磁流体轴承的承载能力得到提高,能在高温、高速的工况下工作。     

磁场中磁流体粘度测试系统的实现

介绍了一种磁流体粘度测试系统，可用于研究磁流体动密封磁场对磁流体粘度的影响。在该系统中驱动外筒的电机转速的变化与填充在固定内筒和外筒之间的磁流体粘度成反比，而模拟磁流体动密封运行工况的磁路则提供了定量的可变的外磁场，另外基于外推法的温度测量方案可精确地对测试时的温度进行控制，最后使用标准液体标定的结果表明其相对误差小于0．83%。     

磁流体密封中转轴偏心时磁场和轴受力的数值计算

在磁流体密封理论及磁场和磁场力计算理论的基础上,用Pro/E和Ansys软件联合建立密封结构的三维模型并用Ansys软件计算磁场分布和磁场力.在验证了计算方法的可行性后,计算某典型的三槽四齿密封结构在密封间隙分别为0.1 mm和0.2 mm时多种偏心量下的磁场分布和转轴受力.结果表明,磁流体的密封耐压随偏心率的增加而减小,且间隙越小,耐压对偏心量的变化越敏感;转轴受到的磁场力随偏心率的增大而增大,且依赖关系近似呈线性.进一步的分析表明,转轴偏心时受到磁场力的作用不是轴承失效的主要原因.     

磁场作用下的Fe3 O4磁流体承载能力的试验研究

通过对MS-800四球机油杯的改进,在测试区域内产生可调磁场,利用该改进后的油杯在四球机上对磁场作用下Fe3O4磁流体承载能力进行测定。试验结果表明,磁流体润滑膜在外加磁场作用下,综合承载能力得到了很大的提高,最大可提高至原来的1.3倍。结合Rosensweig理论模型,通过对磁场下磁流体粘度的测定,分析得出磁流体的粘度变化是引起综合承载能力发生变化的主要原因。     

磁流变阻尼器阻尼通道结构参数对响应时间的影响研究

通过ANSYS软件进行磁场仿真得出了不同磁流体通道间隙,磁极长度,磁极形状以及磁回路厚度下磁流变阻尼器磁感应强度随时间变化的曲线图。通过分析磁场仿真结果得出:随着磁流体通道间隙的增加,其响应时间呈上升趋势;随着磁极长度的增加,其响应时间减小;磁极表面有不同形状,当磁极表面形状为平面且有圆弧倒角时其响应时间最短;活塞磁场未饱和时,随着磁回路的厚度的增加其响应时间增大,当活塞磁场饱和时,磁回路的厚度对磁流变阻尼器的响应时间不会产生影响。     

磁流体密封中黏性损耗对密封性能的影响

磁流体密封中,由于摩擦产生大量的热将会引起温度急剧变化,而黏性损耗则是影响摩擦功耗的一个重要因素。以醇-水共热沉淀法制得的二辛酯基磁流体作为密封介质,研究黏性损耗对磁流体温度场和黏度的影响。结果表明:黏性耗散是引起磁流体温度升高、黏度降低的主要因素,对磁流体密封性能的影响不可忽略;磁场作用明显增大相同转速下磁流体的黏滞损耗,但磁场的大小不对磁流体温度场和黏度变化的影响不大。     

高温熔体粘度仪在半导体熔体研究中应用

本文介绍带可调水平磁场的高精度高温熔体粘度测量仪在半导体熔体粘度测试中的应用。该仪器试验用料少、测试温度范围宽、磁场均匀可调、精度高。利用回转振动法对硅、锗等半导体熔体的粘度进行测试分析,获得许多有意义的结果。     

Flow Properties of Alicyclic Compounds as Traction Fluids

Several alicyclic compounds, model compounds of traction fluids, were synthesized and the high-pressure viscosity was measured with a rolling viscometer. The relation between the molecular structure of the synthetic alicyclic compounds and their activation quantities for viscous flow is discussed. A useful structure-property guideline for the design of better traction fluids is presented. The relation between these flow activation quantities is also discussed. It was found that his relation could be used to estimate the pressure dependence of the viscosity from the temperature dependence of the viscosity.     

A Simple,New Type of Rotational Viscometer

Abstract

The objective of this study was to construct a new type of rotational viscometer and to obtain the temperature dependence of the viscosities of fluids. A beaker containing 80 mL of fluid was rotated and the variation of the angular velocity of the beaker was measured with a photogate using a frequency?voltage converter (FVC). Viscosity measurements were performed while heating the fluid. The variation of the viscosity with temperature was investigated for lubricants. The output of the FVC and the temperature probe (thermistor) were connected to a PC via an analog-to-digital converter (ADC).     

Continuous viscosity measurement of non-Newtonian fluids over a range of shear rates using a mass-detecting capillary viscometer

A newly designed mass-detecting capillary viscometer uses a novel concept to continuously measure non-Newtonian fluids viscosity over a range of shear rates. A single measurement of liquid-mass variation with time replaces the flow rate and pressure drop measurements that are usually required by capillary tube viscometers. Using a load cell and a capillary, we measured change in the mass flow rate through a capillary tube with respect to the time,m(t), from which viscosity and shear rate were mathematically calculated. For aqueous polymer solutions, excellent agreement was found between the results from the mass-detecting capillary viscometer and those from a commercially available rotating viscometer. This new method overcomes the drawbacks of conventional capillary viscometers meassuring non-Newtonian fluid viscosity. First, the mass-detecting capillary viscometer can accurately and consistently measure non-Newtonian viscosity over a wide range of shear rate extending as low as 1 s⁻¹. Second, this design provides simplicity (i. e., ease of operation, no moving parts), and low cost.     

用旋转粘度计法研究非牛顿流体的流变性能

本文主要介绍在5个不同减阻剂浓度(0 mg/L,100 mg/L,200 mg/L,300 mg/L,400 mg/L)和不同温度(15℃,20℃,25℃)下,用旋转粘度计法测定减阻剂样品在7m in内,剪切速率从0~183.45/s下,研究0号柴油及加入减阻剂后的流变性能。一般情况下,幂律模型适合于大部分非牛顿流体。加剂后的柴油溶液,与空白柴油相比较,稠度都有不同程度的提高。在低剪切速率下,大多数实验结果表现为牛顿流体流变行为,但D-41(块)溶液例外,浓度为300mg/L的15℃和20℃及浓度为400mg/L的25℃表现出假塑性流动行为。浓度与粘度的线性关系用关系和指数关系相对于乘幂关系拟合程度较高,而用乘幂关系拟合程度较低。粘度与温度间服从于阿累尼乌斯方程。     

Blood viscosity measurements using a pressure-scanning capillary viscometer

A previously designed capillary viscometer with measuring differential pressure was modified to measure the viscosity of non-Newtonian fluids including unadulterated blood continuously over numerous shear rates in a single measurement. Because of unavoidable experimental noise and a limited number of data, the previous capillary viscometer experienced an inaccuracy and could not directly determine a viscosity without an iterative calculation. However, in the present measurement there are numerous data available near the point of interest so that the numeric-value of the derivative,d(lnQ)/dln τω), is no longer sensitive to the method of differentiation. In addition, relatively low and wide shear rate viscosity measurements were possible because of the present precision pressure-scanning method with respect to time. For aqueous polymer solutions, excellent agreement was found between the results from the pressure-scanning capillary viscometer and those from a commercially available rotating viscometer. In addition, the pressure-scanning capillary viscometer measured the viscosity of unadulterated whole blood without adding any anticoagulants.     

Rotordynamic Analysis of a Shaft Using Magnetorheological and Nanomagnetorheological Fluid Journal Bearings

The rotordynamic behavior of a system supported by journal bearings is critical to its reliability. A suitable method of control of the orbital motion of a shaft in a journal bearing is the use of smart lubricants, in effect fluids with controllable physical properties. There are various categories of smart lubricants. One class of smart lubricants, magnetorheological fluids, are produced as a dispersion of magnetic particles in a carrier fluid, which is usually a conventional lubricant. These particles form chains under the influence of a magnetic field, which hinder the lubricant flow, thus changing its apparent viscosity. Magnetorheological fluids (MRFs) exhibit high yield stress, low delay of response, and relatively low friction while not in their active state. A subcategory of MRFs, nanomagnetorheological fluids (NMRFs) with particle size on the nanometer scale, exhibits lower yield stress than MRFs but display high viscosity. The effect of the MRFs and NMRFs on the rotordynamic behavior of a shaft is calculated through a combined finite element and computational fluid dynamics analysis. Though the MRF with the specific geometrical configuration of the bearing is not sufficiently activated and therefore does not improve the performance of the magnetorheological journal bearing, the NMRF has the ability of limiting up to 82% the amplitude of the vibrations of the shaft.