磁流变技术及应用

介绍磁流变技术的基本情况,磁流变液的组成及磁流变效应的机理;简要阐述磁流变液的流变力学模型和工作模式。对近10年来磁流变技术在机械工程领域等方面的应用进行分类综述,并对其应用前景进行展望。     

Autoregressive trispectrum and its slices analysis of magnetorheological damping device

A combined magnetorheological damper combined with rubber spring and magnetorheological damper is addressed.This type of damping device has inherited the merits of rubber spring and the magnetorheological damper.The test damping device is made up of combined magnetorheological damper,amplitude controller,signal collecting device,computer software for dynamic analysis,etc.When a zeromean and non-Gaussian white noise interfere with the device,a time series autoregressive(AR) model is conducted by using the sampled experimental data.Trispectrum and its slices analysis are emerging as a new powerful technique in signal processing,which is put forward for investigating the dynamic characteristics of the magnetorheological vibrant device.The present of trispectrum and its slices analysis change with the variation of controllable working magnetic field of the damper correspondingly.It is indicated that AR trispectrum and its slices analysis methods are feasible and effective for investigation of magnetorheological vibrant device.     

电流变效应的机理进展

电流变液体是一种由固体小颗粒和绝缘液体组成的智能材料,在电场作用下黏度和软硬度连续可调。在移走电场后,流变性能具有可逆转性,其响应速度极快,可达毫秒级。电流变材料潜在的巨大经济和社会效益使其从20世纪40年代至今一直是一个研究热点。随着材料的研究,相继提出了双电层理论和＂水桥＂机理、极化模型、导电模型以及解释巨ER效应的表面极化饱和模型。综述了电流变效应的传统机理和最新的机理进展模型,介绍了一种适用于颗粒类型电流变液体的剪切应力方程。     

The condensation/polymerisation of dimethyl siloxane fluids in a three-phase trickle flow monolith reactor

For the production of siloxane fluids, the viability of using a multi-channel monolith as a catalyst support system in a three-phase reactor has been studied. The catalyst was tripotassium phosphate (K₃PO₄). Experiments were performed in a single-channel flow reactor (15 mm i.d. and 500 mm catalyst coated length). The rate of reaction was followed by monitoring the disappearance of the hydroxyl group (–OH). Reaction experiments were performed at a hydroxyl group concentration range from 150 to 170 mol m⁻³, T=373–413 K and P=7.9 kPa with a nitrogen purge. The maximum temperature of operation was restricted to 413 K to avoid the formation of undesirable by-products. In the regime controlled by chemical kinetics, reaction was of an apparent first order with respect to –OH concentration, and in the apparent rate constant, the pre-exponential factor was 4.19×10⁻⁴ ms⁻¹, and the apparent activation energy was 16.1 kJ mol⁻¹. These are only valid for the operating pressure and purge gas flowrate used, as both of these are shown to affect water removal from the liquid phase and, hence, reaction rates. Mass transfer coefficients from the liquid to the catalyst surface were estimated and these increased rapidly with flowrate and were higher than expected for a falling liquid film.     

Depletion of cross‐stream diffusion in the presence of viscoelasticity

An effort to analyze the viscoelasticity effects on transverse transport of neutral solutes between two miscible streams in an electrokinetic T‐sensor is presented. The analysis is based on an approximate analytical solution for the depthwise averaged concentration, assuming a channel of large width to depth ratio for which a one‐dimensional profile is sufficient for describing the velocity field. We show that the solution derived is surprisingly accurate even for very small channel aspect ratios and the maximum error reduces to only about 1% when the aspect ratio is 5. The developed model reveals that the mixing length for a viscoelastic fluid may be by far larger than that for a Newtonian fluid. Moreover, the Taylor dispersion coefficient for electroosmotic flow of viscoelastic fluids, which its determination is a main part of the analysis, is found to be an increasing function of both the elasticity level and the EDL thickness. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4533–4541, 2015     

Functionalization of Magnetite Nanoparticles as Oil Spill Collector

In the present study, a new magnetic powder based on magnetite can be used as a petroleum crude oil collector. Amidoximes based on rosin as a natural product can be prepared from a reaction between hydroxylamine and rosin/acrylonitrile adducts. The produced rosin amidoximes were used as capping agents for magnetite nanoparticles to prepare hydrophobic coated magnetic powders. A new class of monodisperse hydrophobic magnetite nanoparticles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The structure and morphology of magnetite capped with rosin amidoxime were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, thermogravimetric analysis (TGA) and dynamic light scattering (DLS). The magnetic properties were determined from vibrating sample magnetometer (VSM) analyses. These prepared magnetite nanoparticles were tested as bioactive nanosystems and their antimicrobial effects were investigated. The prepared nanomaterials were examined as a crude oil collector using magnetic fields. The results show promising data for the separation of the petroleum crude oil from aqueous solution in environmental pollution cleanup.     

Cold Simulation of momentum transfer of a metal droplet falling through slag systems possessing net-work structured fluids

Most of the high temperature smelting/refining processes involve falling of metal droplets through the slag systems. The slag systems comprising oxides viz., Al₂O₃, SiO₂, CaO, FeO, MgO, MnO etc., are essentially produced from the removal of ash and gangue from coke and/or ore during the metal extraction. At high temperatures these oxides form a network structured fluids. Momentum transfer phenomena of a falling sphere through these slag systems significantly influence the kinetics of the refining reactions occurring in the high temperature metallurgical reactors. It governs the metal quality including their productivity. The paper discusses cold simulation of the momentum transfer of a metal droplet falling through the slag systems possessing network structure.     

Effect of the contraction ratio upon viscoelastic fluid flow in three-dimensional square–square contractions

In this work we investigate the laminar flow through square–square sudden contractions with various contraction ratios (CR=2.4, 4, 8 and 12), using a Newtonian fluid and a shear-thinning viscoelastic fluid. Visualizations of the flow patterns were carried out using streak line photography and detailed velocity field measurements were performed using particle image velocimetry. The experimental results are compared with numerical predictions obtained using a finite-volume method. For the Newtonian fluid, a corner vortex is found upstream of the contraction and increasing flow inertia leads to a reduction of the vortex size. Good agreement is observed between experiments and numerical simulations. For the shear-thinning fluid flow a corner vortex is also observed upstream of the contraction independently of the contraction ratio. Increasing the elasticity of the flow, while still maintaining low inertia flow conditions, leads to a strong increase of the vortex size, until an elastic instability sets in and the flow becomes time-dependent at De≈200, 300, 70 and 450 for CR=2.4, 4, 8 and 12, respectively. At low contraction ratios, viscoelasticity brings out an anomalous divergent flow upstream of the contraction. For both fluids studied the flow presents a complex three-dimensional helical vortex structure which is well predicted by numerical simulations. However, for the viscoelastic fluid flow the maximum Deborah number achieved in the numerical simulations is about one order of magnitude lower than the critical Deborah number for the onset of the elastic instability found in the experiments.     

Optimization of in-situ combustion processes: A parameter space study towards reducing the CO2 emissions

Enhanced oil recovery (EOR) through in-situ combustion (ISC) is a process that utilizes a fraction of the oil in-place as fuel in order to upgrade and displace the hydrocarbons in heavy oil reservoirs. In ISC processes, air is injected into a heated section of the reservoir. Upon reaching a threshold temperature, the oxygen in the injected air reacts with the oil in-place and generates heat, a lighter oil fraction, as well as steam and other gaseous reaction products, primarily CO₂, which help drive the upgraded oil (lighter fraction) towards the production wells. ISC processes can, as a result, be highly efficient but at the same time produce significant amounts of CO₂, a potent greenhouse gas. In this paper the emphasis is on developing an ISC process with significantly reduced CO₂ emissions. The process involves the capture and re-injection of CO₂ into the formation. We find that, in addition to reducing the CO₂ emissions, this novel process also shows improved oil recovery rates relative to conventional ISC without CO₂ capture and recycle. We observe, for example, increases in the oil recovery of ∼33% for a fixed time of operation when comparing the ISC process with CO₂ recycle against the conventional ISC process. In addition, at the time when 80% of the total oil in-place has been produced, the CO₂ emissions are consistently lowered by 18–22% when CO₂ is recycled back into the formation. This study analyzes the characteristics and dynamics of the process and explores the effect of the relevant process parameters. For a wide range of Peclet and Damköhler numbers as well as initial saturations, favorable trends induced by CO₂ recycling are observed.     

Wall Effects for the Free Rise of Solid Spheres in Moderately Viscous Liquids

For the first time ever, the influence of wall effects on the free rise of a buoyant solid sphere in a square column in a non‐Newtonian (pseudoplastic) fluid was determined. It was found that in most cases, as the column width decreased, the terminal rise velocity of the sphere would decrease as well. It was also discovered that wall effects could change the rising sphere trajectory. Spheres that displayed a spiraling trajectory in larger columns would display a more linear trajectory in smaller columns. Occasionally, due to this change in trajectory, the solid sphere terminal velocity would increase as the column width decreased. This phenomenon (the positive wall effect) has not been reported for falling spheres in Newtonian or non‐Newtonian fluids.