轻质磁性材料的制备及在磁流变液中的应用

研究了使用化学镀的方法在轻质载体上包覆具有磁性的镍、钴等物质。该材料具有密度低的优点（有效密度为2-3g/cm^3）。对比于几种羰基镍粉制备的磁流变液的沉降稳定性,使用该轻质磁性材料制备的磁流变液不用加防沉剂,其稳定性类似于加入较多防沉剂的羟基镍粉磁流变液。其在磁场下表观粘度比零磁场下的粘度有几十倍的变化。因此,使用该轻质磁性材料有望解决磁流变液普遍存在的沉降问题,得到综合性能良好的产品。     

高性能石油焦颗粒电流变液的研究

采用未经精制的石油催化裂化油浆的一步炭化产物,研究了将其作为电流变液粒子的可能性、条件和电流变性能。研究结果表明,经由油交论所得焦化颗粒配制的电流变液的力学性能,在2kV/mm直流场强下可达2kPa以上,电流密度不超过60μA/cm^2,长期静置颗粒无明显沉降,是一种性能优良的实用型电流变液。     

磁性粒子浓悬浮体系沉降稳定性的光学表征

报道一种新的磁性粒子浓悬浮体系沉降稳定性的表征方法。对均匀分散的磁性粒子浓悬浮体系,采用定时光度测量法对其沉降稳定性进行表征,可以得到一定时间内粒子沉降的定量数据。此方法可用于低体积分散磁流变液沉降稳定性的表征。同时,对比分析表明,在磁性粒子浓悬浮体系中加入纳米级TiO2粒子,能使制备的磁流变液稳定性显著增强。     

电流变液与电-磁流变液的衍射特性

本文把电流变液装置作为反射光栅研究其衍射特性,首次提出由电场强度改变来调节光栅常数的概念.并讨论了同时外加电场与磁场的情况下,电磁流变液的衍射特性.     

磁流变智能液场致微结构变化的Monte Carlo模拟

从磁流变液中存在的各种相互作用势出发，对Ｎ＝１００个球形羰基铁颗粒均匀分布于一正方形二维体系之中的物理模型，利用ＭｏｎｔｅＣａｒｌｏ方法和Ｍｅｔｒｏｐｌｉｓ算法着重计算了磁流变智能液的场致微结构变化。计算结果表明，磁流变液（ＭＲＦ）的流变效应在外磁场中的变化是由于其ＭＲＦ中磁性颗粒的成链团簇有序化所致。这与磁流变液在外磁场中熵的下降和对ＭＲＦ的光学显微镜观察结果是一致的。     

盘式磁流变液制动特性演示仪的设计

磁流变液是一种在磁场作用下其流变学性能可作出迅速响应, 且易于控制的新型智能材料. 为了演示 磁流变液的制动特性,设计了一种盘式磁流变液制动特性演示装置,介绍了装置的设计原理和工作方法. 该装置通 过演示磁场、扭矩、转速之间的变化关系,对磁流变液的制动特性做了直观形象的展示     

碳化硅基底改性硅表面的磁流变抛光EI北大核心CSCD

为克服传统抛光方法在硅改性的碳化硅表面抛光存在的不足,采用磁流变抛光在精抛光阶段实现面形误差高效去除和快速收敛。基于实际应用中的对磁流变抛光液的需求,提出了磁流变液的性能要求,并配制了适合改性硅表面抛光的磁流变抛光液,检测所配制的抛光液体的流变特性和分散稳定性,证明了液体具有良好的性能。对口径为130 mm(有效口径为120 mm)的硅改性的同轴非球面碳化硅工件进行实际抛光。经过两个周期约3 h的抛光,面形误差均方根(RMS)从0.051λ(λ=632.8 nm)快速收敛至0.012λ,粗糙度Ra达0.618 nm。验证了所配制的磁流变抛光液满足碳化硅基底改性硅表面的抛光需求,证明了磁流变抛光技术在镜面硅改性后精抛光阶段具有独特的优势。     

碳化硅基底改性硅表面的磁流变抛光

为克服传统抛光方法在硅改性的碳化硅表面抛光存在的不足,采用磁流变抛光在精抛光阶段实现面形误差高效去除和快速收敛。基于实际应用中的对磁流变抛光液的需求,提出了磁流变液的性能要求,并配制了适合改性硅表面抛光的磁流变抛光液,检测所配制的抛光液体的流变特性和分散稳定性,证明了液体具有良好的性能。对口径为130 mm(有效口径为120 mm)的硅改性的同轴非球面碳化硅工件进行实际抛光。经过两个周期约3 h的抛光,面形误差均方根(RMS)从0.051λ(λ=632.8 nm)快速收敛至0.012λ,粗糙度Ra达0.618 nm。验证了所配制的磁流变抛光液满足碳化硅基底改性硅表面的抛光需求,证明了磁流变抛光技术在镜面硅改性后精抛光阶段具有独特的优势。     

电流变阻尼器的抗冲击性能研究

从理论和试验两个方面研究了所设计的电流变阻尼器在大冲击下的抗冲击性能,分析了电流变液性能与阻尼器结构参数对抗冲击性能的影响。认为采用高性能的电流变液体及改变结构参数,都可以使电流变阻尼器的高速缓冲性能提高。电流变液流速对电流变液的屈服应力影响显著,其值随流速的增加按指数规律减小。从定性、定量两个方面分析了电流变阻尼器作为阻尼器效果不明显的原因为：由电流变效应引起的阻尼力在整个液压阻力所占比例太小,不能通过改变电压来使液压阻力具有很大的调节可控范围。     

光学玻璃研抛用磁流变液的研究

利用智能材料之一的磁流变液 (MRfluids)作为加工工具对光学玻璃进行了精密抛光加工。讨论了适用于光学玻璃抛光的磁流变液的配制机理及磁流变液对光学玻璃抛光效果的影响因素。针对光学玻璃磁流变的抛光原理和特点 ,开发配制了适合于光学玻璃加工用的磁流变液 ,并用该磁流变液对光学玻璃进行了实验加工。结果表明 ,最终得到的光学玻璃表面经过AFM测试 ,得到Ra =1 0 1 5nm。     

Comment: On charged analogue of shear-free fluids

Recently, Gupta et al. [2] claim that solutions with NDG have no uncharged analogue. This claim seems to be partially correct as it is seen in present article that neutral shear-free fluid (f =α₁ x ^−5/2α₁ being a constant) given by Stephani [3] can be charged.     

非牛顿流体二维溃坝问题的数值模拟

移动粒子半隐式法(Moving Particle Semi-implicit,MPS)是一种广泛应用于不可压缩自由表面流动的粒子方法。本文通过把非牛顿流体转化为变黏度牛顿流体的处理方法将MPS方法拓展至非牛顿自由表面流动,以Casson流体和Cross流体为例计算了非牛顿流体的二维溃坝问题。将计算结果与前人数据进行了对比,结果吻合较好。同时对比了非牛顿流体与牛顿流体的计算结果,发现非牛顿流体的溃坝前端发展速度较慢。     

Electric field dependence of phase equilibria of binary Stockmayer fluid mixtures

A perturbation theory based study of the effect of an external electric field on the phase equilibrium properties of binary Stockmayer fluids is presented. The dipole–dipole interaction and the applied field are treated as independent perturbations to a Lennard–Jones mixture, and the reference fluid is treated by the van der Waals one-fluid approximation. A third-order free energy expression in the electric field strength is established, and the dielectric constant is calculated for a needle-shaped sample parallel to the field direction. We present and discuss vapour–liquid and liquid–liquid equilibrium curves at a given temperature for some dipolar mixtures exposed to an electric field, including chlorodifluoromethane +?difluoromethane and acetonitrile +?methanol. A sufficiently high electric field may result in massive shifts of vapour pressures and critical or azeotropic points, and can considerably alter the properties of coexisting phases. The vapour pressure decreases with increasing field strength.     

A point source solution for unidirectional flow of a viscoelastic fluid

A Fourier point source solution modelling the effect of an impulse on a viscoelastic fluid of second-grade is investigated. By examining the second-moment of a Fourier point source solution we show that for Dt1, where D=ν/ for ν the kinematic viscosity, a viscoelastic parameter and t the time; the fluid undergoes superdiffusion indicating the dominance of the fluids viscoelastic properties. For Dt1 the fluid undergoes classical diffusion indicating that the viscous properties of the fluid are dominating.     

Stationary thermal convection in a viscoelastic ferrofluid

We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. We focus in the stationary convection for idealized boundary conditions. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system. Close to bifurcation, the coefficients of the corresponding amplitude equation are determined analytically. Finally, the secondary instabilities are performed.     

Thermal convection thresholds in a Oldroyd magnetic fluid

We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. The viscoelastic properties is given by the Oldroyd model. We obtain explicit expressions for the convective thresholds in terms of the parameters of the system in the case of idealized boundary conditions. We also calculate numerically the convective thresholds for the case of realistic boundary conditions. The effect of the Kelvin force and of the rheology on instability thresholds for a diluted suspensions are emphasized.     

Integral equation theory of a one dimensional hard-ellipse fluid between hard walls

Density functional theory is used to study the structure of a one dimensional fluid model of hard-ellipse molecules with their axes freely rotating in a plane, confined between hard walls. A simple Hypernetted chain (HNC) approximation is used for the density functional of the fluid and the integral equation for the density is obtained from the grand potential. The only required input is the direct correlation function of the one dimensional hard-ellipse fluid. For this model, the pressure, sum rule and the density at the walls are obtained. The Percus Yevick (PY), for lower density, and HNC, for higher density, integral equations are also solved to obtain the direct correlation function of hard-ellipse model introduced here. We obtain the average density at the wall as well as the radial density profile. We compare these with Monte Carlo simulations of the same model and find reasonable agreement.     

Existence of a Hartmann layer in the peristalsis of Sisko fluid

Analytical solutions for the peristaltic flow of a magneto hydrodynamic(MHD) Sisko fluid in a channel, under the effects of strong and weak magnetic fields, are presented. The governing nonlinear problem, for the strong magnetic field,is solved using the matched asymptotic expansion. The solution for the weak magnetic field is obtained using a regular perturbation method. The main observation is the existence of a Hartman boundary layer for the strong magnetic field at the location of the two plates of the channel. The thickness of the Hartmann boundary layer is determined analytically. The effects of a strong magnetic field and the shear thinning parameter of the Sisko fluid on the velocity profile are presented graphically.     

Investigation into the protein composition of human tear fluid using centrifugal filters and drop coating deposition Raman spectroscopy

Drop coating deposition Raman spectroscopy (DCDRS) is a simple method of analysing weak protein solutions. This study is another step in evaluating the analysis of tear fluid by DCDRS as a future medical diagnostic technique. The main aims of this study are to determine whether the DCDR spectra from tear samples contain signals from more than one protein (so relative levels can be measured) and, if so, are the proteins homogeneously distributed in the dried ring of the deposited material. Tear samples were collected from four healthy volunteers and pooled prior to analysis. Proteins were separated by mass into three groups using centrifugal filters. These groups contained proteins with (1) masses greater than 100 kDa, (2) masses between 100 and 50 kDa and (3) masses between 50 and 3 kDa. DCDR spectra from each of these protein group solutions displayed significant differences, confirming that the mass separation had been successful. When used as basis vectors for least‐squares fitting, these spectra (and that of urea) produced excellent fits to the normal tear spectra. Least‐squares fitting of spectra from the same point on a single sample and from several drops of the same sample showed that the tear DCDR spectra were highly reproducible. Raman point mapping of the tear ring showed significant radial ring variation, especially towards the outer edge of the ring. The specific peak changes in the protein signal across the ring suggested that the difference in the outer edge was due to protein desiccation as opposed to inhomogeneous protein deposition. Copyright © 2008 John Wiley & Sons, Ltd.     

竖管中CO2泡沫压裂液的管流阻力特性

CO2泡沫压裂液具有非牛顿流体性质,其在实际施工条件下的油管流动特性直接影响到对井底射孔处的压力确定,从而对进行准确的裂缝预测、压裂效果评估具有重要的意义。对垂直下降管中CO2泡沫压裂液的管流阻力特性进行了实验研究,二氧化碳泡沫压裂液的摩擦阻力随着流速的增大而增大,随着温度和压力的增大而减小;并通过实验研究得出了泡沫压裂液在垂直下降管中流动时的摩擦阻力系数的计算关联式,其在本文实验工况下的平均计算误差为14.8％。