A lubrication theory for fluids with microstructure

Experimental observations indicate that viscosity of fluids adjacent to solid surfaces is altered as compared to bulk viscosity measured away from the surfaces. It is well-established that in thin films of less than several molecules thick, the classical Reynolds theory of lubrication breaks down and there is at present no microscopic model for the flow behavior of a collection of molecules near a solid wall. In this paper, a nonlocal lubrication theory of fluids with microstructure is presented to provide a basic theory for calculatin the rate at which a thin film of liquid drains from between two molecularly smooth, solid surfaces as they are forced together. The viscosity moduli, proposed by the theory are in excellent agreement with experiments for all film thicknesses down to zero. Exact solutions are obtained for drainage curves and for the spread of thin films on a rotating surface. Theoretical calculations are in perfect agreement with several experimental observations.     

Effect of viscous dissipation on the lubrication characteristics of micropolar fluids

Summary Thermohydrodynamic solutions are presented for a finite journal bearing lubricated with micropolar fluid. Comparison with isothermal results, assuming that viscosity remains at the inlet temperature, is also given. Results indicate the heat generation due to viscous dissipation plays an important role on the load-carrying of a journal bearing lubricated with micropolar fluids.     

Non-classical kinematic shocks in suspensions of particles in fluids

Summary The properties of weakly nonlinear kinematic waves in suspensions are investigated under the assumption that the particle concentration deviates only slightly from the value at the inflexion point of the drift flux curve. Special emphasis is placed on the conditions for the existence of an internal dissipative-dispersive shock structure. The resulting shock admissibility criteria are found to be significantly different from those following from standard theories of kinematic waves. Most interesting, the analysis shows that non-classical shocks which emanate rather than absorb characteristics may be admissible under certain conditions.     

Using light to study boundary lubrication: spectroscopic study of confined fluids

Several instrumental developments to examine the spectroscopic response of molecularly thin fluids confined between mica sheets are described. They are predicated on using a redesigned surface forces apparatus where dielectric coatings, transparent to light at needed optical wavelengths, retain the ability to measure interferometric thickness at other optical wavelengths. Examples of recent measurements are presented using confocal laser Raman spectroscopy to evaluate how molecules orient as well as to perform chemical imaging. Other examples are presented using confocal fluorescence recovery after photobleaching to evaluate translational diffusion of confined polymer melts. The advantage of separating the mechanical average (force and friction) from direct information about structure and mobility at the molecular level is stressed.     

Weakly nonlinear kinematic waves in suspensions of particles in fluids

Summary The properties of weakly nonlinear kinematic waves in suspensions are investigated under the assumption that the particle concentration deviates only slightly from the value at the inflexion point of the drift flux curve. Special emphasis is placed on the mechanism of shock splitting and the properties of the shock structure.     

杆形颗粒磁流变液的剪切屈服应力模型

杆形颗粒磁流变液是新近出现的新型磁流变液,它比传统磁流变液具有更好的性能.基于磁力学理论,通过分析磁化链中杆形颗粒的受力,包括磁力、压力、摩擦力及磁场对颗粒的力矩等,建立了磁流变液的剪切屈服应力模型,并和球形颗粒磁流变液加以对比,发现杆形颗粒磁流变液具有更高的屈服应力.计算结果和实验数据的比较表明,该模型能描述不同磁场...     

Accurate treatment of lubrication forces between rigid spheres in viscous fluids using a traction-corrected boundary element method

Traditional boundary element methods cannot accurately resolve lubrication forces in the interstitial regions between nearly touching particles in viscous flows. In many cases, the interstitial tractions are underestimated and the relative particle velocities are overestimated resulting in significant errors in predicting particle trajectories. In order to accurately treat the lubrication forces between nearly touching particles, a traction-corrected boundary element method (TC-BEM) for multiple particles is developed by combining the analytical asymptotic solution for the tractions in the interstitial regions with the boundary element method. An adaptive meshing algorithm is developed to provide appropriate meshes on surfaces of particles with close interactions. The numerical method also employs an efficient parallelization scheme to make possible prediction of long-time behavior of particles suspended in viscous flow fields. The results of the TC-BEM are benchmarked by comparisons to analytical results for two particles in a linear shear flow and by considering the reversibility of three particles in a circular Couette flow. It is shown that the TC-BEM is able to correctly resolve the lubrication forces between nearly touching particles, thus enabling the accurate analysis of particles suspended in nonlinear shear flows.     

Magnetic particles stabilized by chemically adsorbed monolayers for use in functional fluids

Chemically adsorbed monolayers were applied to magnetic particle surfaces for preparing functional fluids. Fluorocarbon silanes were used to form the monolayers, as the methoxysilyl groups of fluorocarbon silanes can form a strong chemical bond with the surface of a magnetic particle without degrading its properties. Fluorocarbon oils were used as the carrier liquid because of their high affinity with the fluorocarbon group of the monolayers, enabling the particles to disperse easily in it. Also, fluorocarbon oils can sustain high temperature and low pressure. The functional fluids prepared using these materials showed magnetorheological characteristics and can be used under high-vacuum and/or high-temperature conditions like those encountered in space.     

AC electrothermal manipulation of conductive fluids and particles for lab-chip applications

AC electrokinetics has shown great potential for microfluidic functions such as pumping, mixing and concentrating particles. So far, electrokinetics are typically applied on fluids that are not too conductive (<0.02 S/m), which excludes most biofluidic applications. To solve this problem, this paper seeks to apply AC electrothermal (ACET) effect to manipulate conductive fluids and particles within. ACET generates temperature gradients in the fluids, and consequently induces space charges that move in electric fields and produce microflows. This paper reports two new ACET devices, a parallel plate particle trap and an asymmetric electrode micropump. Preliminary experiments were performed on fluids with conductivity at 0.224 S/m. Particle trapping and micropumping were demonstrated at low voltages, reaching ~100 mum/s for no more than 8 Vrms at 200 kHz. The fluid velocity was found to depend on the applied voltage as V⁴, and the maxima were observed to be ~20 mum above the electrodes     

Voltammetric behaviour of nitroxazepine in solubilized system and biological fluids

This study reports the development and validation of sensitive and selective assay method for the determination of the antidepressant drug in solubilized system and biological fluids. Solubilized system of different surfactants including cationic, anionic and non-ionic influences the electrochemical response of drug. Addition of cationic surfactant cetrimide to the solution containing drug enhances the peak current signal while anionic and non-ionic showed an opposite effect. The current signal due to reduction process was function of concentration of nitroxazepine, pH, type of surfactant and preconcentration time at the electrode surface. The reduction process is irreversible and adsorption controlled at HMDE. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for niroxazepine hydrochloride determination. The proposed SWCAdSV and DPCAdSV methods are linear over the concentration range 2.0 × 10^-7– 5.0 × 10^-9 mol/L and 6.1 × 10^-7– 1.0 × 10^-8 mol/L with detection limit of 1.62 × 10^-10 mo/L and 1.4 × 10^-9 mo/L respectively. The method shows good sensitivity, selectivity, accuracy and precision that makes it very suitable for determination of nitroxazepine in pharmaceutical formulation and biological fluids.     

Noise-induced transitions in a system of coagulating particles

Rigorously solvable models of the system of coagulating particles in a stochastic medium are proposed. It is demonstrated that such systems are featuring additional noise-induced stationary states. The results are considered from the standpoint of using this phenomenon for evaluating the effective parameters of the medium.     

Real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids

Cluster movements of ferro- and non-magnetic particles in magnetic fluids were investigated using optical microscope system and image processing system. Real-time visualizations of the Brownian motion of particles and the chain-like cluster movement of both types of particle were performed under a magnetic field. The principal objectives of this study were to clarify the applicability of the optical microscope system and image processing system, and to analyze the growth process of the cluster under magnetic field. The analysis of particle image was done using Particle Tracking Velocimetry (PTV). The results clarified that the real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids can be carried out using the optical microscope system and the PTV image measurement. Independent continuous measurements with changing positions and velocity of the minute particle were made possible. The study concluded that the system can obtain satisfactory results on growth process measurement of cluster under a magnetic field.     

Real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids

Cluster movements of ferro- and non-magnetic particles in magnetic fluids were investigated using optical microscope system and image processing system. Real-time visualizations of the Brownian motion of particles and the chain-like cluster movement of both types of particle were performed under a magnetic field. The principal objectives of this study were to clarify the applicability of the optical microscope system and image processing system, and to analyze the growth process of the cluster under magnetic field. The analysis of particle image was done using Particle Tracking Velocimetry (PTV). The results clarified that the real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids can be carried out using the optical microscope system and the PTV image measurement. Independent continuous measurements with changing positions and velocity of the minute particle were made possible. The study concluded that the system can obtain satisfactory results on growth process measurement of cluster under a magnetic field.     

Functionalized nano-magnetic particles for an in vivo delivery system

Nanotechnologies to allow the nondisruptive introduction of carriers in vivo have wide potential for therapeutic delivery system. We have prepared functional nano-magnetic particles (d = 3 nm) by silanization with (3-aminopropyl) triethoxysilane. For the purpose of functionalizing the surface of the nanoparticles with amino groups for subsequent cross-linking with pharmaceuticals and biomolecules. The extremely small particles were successfully introduced into living cells without any further modification to enhance endocytic internalization, such as the use of a cationic help. The cells containing the internalized particles continued to thrive, indicating that the particles have no inhibition effect for mitosis. In addition, the particles could be incorporated into the subcutaneous tissue of mouse's ear from ear skin and were able to be localized upon application of an external magnetic field. The functionalized nano-magnetic particles are expected to be useful as a new delivery tool.     

Boundary element method of multi-lobe hydrodynamic lubrication bearing for numerical analysis in lubrication theory

In the present paper, the hydrodynamic lubrication problems of multi-lobe bearings are treated by the Boundary Element Method in lubrication theory. For example, we have made numerical calculations for elliptical bearings and three-lobe bearings. The stress and pressure distributions on the bearings and the velocity fields of the lubricant are given. We also studied conditions for the occurrence of vortexes in the flow region. The numerical investigations have shown that the method is very effective in handling hydrodynamic lubrication problems and it can be used to study the vortex in arbitrary shape bearings. Furthermore, the method has some advantages of computational convenience and superior accuracy. Especially, the ending point of the oil film pressure can be ascertained when non-linear terms are considered, and that is undoubtedly extremely important in studying hydrodynamic lubrication problems.     

A power transducer system for the ultrasonic lubrication of the continuous steel casting

A critical point in the continuous steel casting process exists in the meniscus zone of the cooled mould, i.e., the region in which the steel stream flowing out of the tundish nozzle starts to solidify. This is a critical point because of the sticking that occurs between the solid shell of steel and the mould. In this work, a new system for the ultrasonic lubrication of the continuous steel casting is proposed and experimentally tested. The basic idea is to excite one of the mould's natural vibration modes by means of a distributed ultrasonic source. This source is composed of an array of power emitters, with each of them placed upon an antinode of the mould. An experimental characterization of the vibrational behavior of a square mould was first carried out. The most active resonance modes of the mould were detected with an experimental technique based on a simple impedance measurement. The modal shape of the selected mode, and hence the position of antinodes, was obtained by means of interferometer measurements. Additional experimental investigations were performed by exciting mould vibrations with up to four piezoceramic disks placed on different sets of antinodes. Some positioning criteria to maximize the superposition effect were derived. Measurements were obtained through excitation of the mould with up to four Langevin-type power emitters, designed and manufactured to work at the mould's selected resonance frequency. These measurements have shown that, by increasing the number of emitters, the ultrasonic power transmitted to the mould and, consequently, the maximum available displacement, increases. Other practical advantages of the proposed system are highlighted and discussed.     

Continuous reactor system of monosized colloidal particles

A reactor system, which continuously hydrolysed the metal alkoxide in an alcohol solution, was designed using an electromagnetic stirrer and an ageing tube. Several monosized colloidal particles were produced by this reactor system, which had high reproducibility and reliability for long-term production. The relation between powder characteristics and experimental parameters such as reagent concentration, mixing rate, ageing time, temperature, was investigated. These parameters had an effect on the particle size, size distribution, morphology and state of agglomeration. It is possible to control the particle size to between 0.1 and 1.0 μm by varying the experimental conditions. A narrower size distribution of powders was obtained by using an electromagnetic stirrer with greater flow rate. Physical and chemical properties of monosized colloidal particles obtained by this reactor were comparable to those of monosized colloidal particles obtained by the batch process.