Particle Flocculation and Filtration by High-Gradient Magnetic Fields

Abstract

Flocculation and filtration of micrometer-sized particles in a high-gradient magnetic field (HGMF) were investigated. Experiments were conducted using a cryogenic magnet of 6 Tesla maximum strength. Hematite particles were used for flocculation and filtration experiments. A new approach of using magnetic fields to enhance separation of weakly magnetic particles was also investigated. This approach is based on magnetic seeding which involves flocculation of existing nonmagnetic particles with injected paramagnetic particles. A particle-flocculation model was developed based on trajectory analysis. External forces due to gravity and magnetism, and interparticle forces such as electrostatic, hydrodynamic, magnetic dipole, and van der Waals forces, were taken into consideration in these models.

     

磁性液体在外施磁场下的方向性弱絮凝行为

磁性液体是一种高分子稳定胶体,实验观察发现磁性液体在外施磁场作用下,磁性颗粒沿着外磁场方向形成一定有序排列的球链簇,却又不是絮凝使胶体系统失稳,显示出与其它胶体系统的不同之处。在一般胶体系统中弱絮凝行为表现不明显,不引起重视,通过计算分析发现磁性液体在外加磁场下弱絮凝行为表现却异常明显,而且弱絮凝行为存在着方向性,又不使胶体系统失稳,与实验和实际应用相符。从而揭示了磁性液体在外施磁场作用下各向异性的机理,并且很好地解释了光波在在外施磁场作用下的磁性液体中会产生光的双折射效应等现象。     

磁粒研磨中单颗磁性磨粒磁场力的实验研究

为了解决单颗磁性磨粒其磁场力难以定量分析和测量的问题,本文通过对现有磁场力理论进行分析,利用特斯拉仪对永磁极轴线方向上的磁场强度进行测量,并利用MATLAB对磁场强度的实际测量值进行数值拟合,得出了磁场强度关于加工距离的函数曲线,进而获得磁场强度变化率的函数曲线,以其代替理论公式中的磁场强度梯度推导得出了便于定量分析的...     

Velocity Field Structure and Flocculation Efficiency in Taylor-Couette Flow

Velocity field data were acquired for Taylor-Couette flow in the annulus gap between a rotating inner cylinder and a fixed concentric outer cylinder by using particle image velocimetry. The flocculation efficiencies were also obtained in the same Taylor-Couette flow under the conditions corresponding to the velocity field measurement. The flocculation efficiencies reached the maximum values due to the closed vortices, their contraction and expansion with time in wavy vortex flow. But out of the wavy vortex flow range, the comparatively low flocculation efficiencies were obtained due to the no-closed vortices which connected with each other.     

PEMFC Performance in a Magnetic Field

A polymer electrolyte fuel cell is operated in a magnetic field gradient (B × dB/dx = ±3 T²�m^–1) and the power output is investigated at lower partial pressure of oxygen gas and lower temperature than customarily used in fuel cells. The effects of the magnetic field are not confirmed at the cell current of i < 12 mA cm^–2. On the other hand, the cell performance is improved or deteriorated depending on the direction of the magnetic field gradient at higher current densities at which the mass transfer of oxygen gas is limited by diffusion. The results suggest that the magnetic field influences the diffusion process of the oxygen molecules rather than the catalysis.     

Instability of a Magnetic Fluid Jet in a Transverse Magnetic Field

The instability behavior of moving magnetic fluid jet in the presence of a constant uniform transverse magnetic field is investigated theoretically within the framework of linear stability analysis. The corresponding dispersion relation between the wave growth rate of instability and the magnitude of its wavenumber is obtained. The dependence of the wave growth rate on the polar angle in the presence of magnetic field is found. The influence of the magnetic field on the length of undisturbed jet section and the instability wavelength is studied. The correlation with the experimental results is demonstrated.     

Flocculation and Separation of Oil Droplets in Ultrasonic Standing Wave Field

A new method for breaking oil in water emulsion based on flocculation of droplets in high intensity ultrasonic standing wave field was developed in this study and the effect of initial droplets size, type of disperse phase as well as the time of sonication and the height of emulsion in the chamber on the extent of interdroplet interactions were investigated. The results showed that type of disperse phase affects the efficiency of separation process through controlling the initial size of droplets. For the two types of disperse phase in question the efficiency of separation was calculated to be 42.7% for canola oil/water emulsion and 37% for sunflower oil/water emulsion. The time of sonication was found to have a positive contribution to the percent of flocculation and coalescence, so that the largest aggregates were formed after 30 minutes treatment. Also, the optimum height of emulsion in the treatment chamber was determined to be λ/4 at which the strongest flocculation and highest percent of coalescence took place. Increasing the height of emulsion did not significantly influence the course of aggregation and separation.     

Electromagnetic Field and Current Waves in a Conductor Compressed by a Shock Wave in a Magnetic Field

A physically correct and mathematically rigorous solution of the problem on the structure of an electromagnetic field formed when a shock wave enters a conducting half–space in a transverse magnetic field is obtained. It is shown that only physically grounded boundary conditions lead to a noncontrovercial pattern of the electromagnetic field and a system of currents in a conductor. The main parameters and characteristic times are found, which determine the structure of current waves in a metal. The solution in the uncompressed region is determined by the parameter R₁ = µ₀₁D²t and that in the compressed region by the parameter R₂ = µ₀₂(D—U)²t (₁ and ₂ are the electric conductivities of the uncompressed and compressed substance, respectively, µ₀ is the magnetic permeability of vacuum, D is the wave–front velocity, U is the mass velocity, and t is the time). The parameter for the compressed substance R ₂ coincides with the parameter obtained previously for the shock–wave dielectric—metal transition; the governing parameter for the uncompressed substance R ₁ is obtained for the first time. The asymptotic solutions of the problem for small and large times and the special case R ₁ = R ₂ considered help in understanding the physical meaning of the solution found.     

Assessment and Mechanism Investigation of Selective Flocculation Process for Ultrafine Chromite Particle

During beneficiation of low-grade chromite ore, huge amounts of ultrafine tailings are generated and contain substantial metal values which need to be recovered. Selective flocculation technique is one of the processes for beneficiation of ultrafine particles. Here an attempt was made to establish selective flocculation process by using two types of synthetic mixtures. In addition to this, selective flocculation was also attempted on natural tailings. It was found that it is possible to enrich the chromite value using the selective flocculation process. The selectivity of the wheat starch to the chromite mineral was also investigated using image analysis, FTIR analysis, and zeta potential analysis.     

Separation of Phosphorus and Magnetic Mineral Fines from Siderite Reductive Ore by Applying Magnetic Flocculation

The characteristics of siderite reductive ore and the ultrafine grinding-magnetic flocculation separation (MFS) of this ore were investigated in the present work. The results indicated that the iron phase in the raw ore was predominantly metallic iron with an iron particle size below 30 μm, and the phosphorus compound was apatite. By applying MFS to siderite reductive ore containing 37.14% Fe and 0.52 P, a concentrate assaying 66.37% Fe and 0.19 P with 74.32% recovery was produced. The iron recovery increased by 5.77% compared with the results of the conventional magnetic separation. The high efficiency in phosphorus removal and iron recovery achieved by the MFS process may be attributed to the adequate liberation of iron particles and the increase in magnetic force on the iron mineral fines in the form of flocs in a magnetic field.     

Study of a Magnetic Filter System for the Characterization of Particle Magnetic Property

A magnetic filter system has been constructed, and its performance has been investigated, to measure the magnetic property of monodisperse γ -Fe ₂ O ₃ particles in the size range from 100 to 300 nm. In the system, SS 430 screens are placed in the magnetic filter element and exposed to a strong external magnetic field generated by an electric coil. The high magnetic field gradient resulted from magnetized fine wires enhances the collection of magnetic particles in addition to the particle collection via the diffusion mechanism. The particle concentrations at the upstream and downstream of the magnetic filter element were measured by an Ultrafine Condensation Particle Counter (UCPC, TSI model 3025A). Particle penetration obtained in the experiment is a function of particle size, particle magnetic property, and wire magnetization. To retrieve the magnetic property of characterized particles from the measured penetration data, a numerical model was further developed using the finite element package COMSOL Multiphysics 3.5. In this modeling, a single mesh screen is assumed to be represented by unit cells. The flow, the magnetic fields, and particle trajectory were solved in a unit cell. The relationship between particle penetration and magnetic property can then be obtained via this model for the given particle size, aerosol flowrate, and external magnetic field strength. The numerical model was first validated by comparing the experimental penetration with the simulation results for the case of 100, 150, and 250 nm γ -Fe ₂ O ₃ particles having the magnetic susceptibility characterized by Vibrating Sample Magnetometer (VSM). The magnetic susceptibilities of other sizes from 100 to 300 nm were then derived from this model according to the measured penetration data.     

磁粉检测的可靠性

分析了磁粉检测理论和磁粉检测工艺过程,讨论了影响磁粉检测可靠性的主要因素和提高磁粉检测可靠性的措施。     

Copper Ion Cementation in Presence of a Magnetic Field

The effect of an electromagnetic field (EMF) on the rate of copper(II) cementation from copper sulfate solutions on a rotating iron cylinder was investigated. The studied variables were cylinder rotation speed, magnetic field strength, and magnetic field direction. The application of EMF increased the rate of cementation in both parallel and perpendicular direction of the magnetic field where the latter proved to be more effective. The rate of mass transfer under an EMF was found to be more than doubled. The enhancement of copper recovery in presence of the EMF is due to the induced motion of Fe⁺ⁿ in the solution which is limited to a certain range of cylinder rotation speed. The power consumption for cementation of copper could be significantly reduced by utilizing EMF.     

Magnetic Field,Flow Field and Inclusion Collision Growth in a Continuous Caster with EMBR

A three‐dimension mathematical model has been developed to describe the magnetic field, fluid flow and inclusion transport in a continuous caster with electromagnetic brake (EMBR). According to the model, all the governing equations can be expressed as a general differential equation, so a general numerical method was developed to solve these equations. The numerical results agree well with the experimental result. In the continuous caster, the inclusion distributions have ‘M’ shape under the nozzle and ‘W’ shape at the exit, which come from the centrifugal effect and the collision and aggregation among inclusions. The three‐dimensional static magnetic field can effectively damp local flows and affect the inclusion transport in a continuous caster. If EMBR is installed under the nozzle, it can promote the inclusion removal and the inclusion ‘M’ distribution disappears.     

气田絮凝除油试验研究

以海上某气田生产污水为研究对象,根据生产污水性质,开发一种以聚胺类表面活性剂为主剂、水溶性高分子为辅剂的复合絮凝剂。该复合絮凝剂通过阳离子型高分子多元共聚物分子链上的支链结构,使药剂体系具有较强的网捕和桥接性能,实现气田生产污水的快速沉降分离。该药剂在气田进行了现场试验,试验期间处理水水质完全达到气田排海要求,且在溶解油去除方面有很大改善。     

磁编码器多极磁鼓空间磁场分布研究

本文通过对磁编码器磁鼓空间磁场分布的理论计算和定性分析,找出场点位置、磁极数、磁层厚度和磁鼓形状等因素对磁场空间分布的影响,阐明在一定条件下,磁阻探头存在一最佳空间放置点。     

The Effect of Ozonation on Particle Size Distribution for Recirculating Aquacultural Seawater: Analysis of Particle Flocculation and Breakup

ABSTRACT

Solids removal is very important for water quality maintenance in recirculating aquaculture systems (RAS). Ozonation is a practical water treatment which can promote the solids removal. However, the characteristics of ozonation effects on particles are still unclear. In this study, the effect of ozonation on particle size distribution (PSD) was investigated for seawater from a RAS of Pacific white shrimp (Litopenaeus Vannamei). Both flocculation and breakup of particles were demonstrated during ozonation treatment, which resulted in changes of PSD. By using a fractal characteristic value (D_f), the flocculation process could be divided into three stages of preparation, growth and steady. Besides, the flocculation efficiency varied parabolically with contact time. A higher ozone dosage resulted in a shorter preparation stage, along with a longer growth stage (namely lasting a longer flocculation effect) and thus a relatively higher limit of parabolic flocculation efficiency. However, the limit would reach a peak and probably be accompanied with a more breakup of particles. The best flocculation efficiency was 43% at ozone dosage of 3.5 mg/L with 5 min contact time. Furthermore, a higher ozone dosage could produce more ammonia.     

高压脉冲电絮凝+加载磁絮凝工艺处理电镀废水

电镀废水中含有大量难降解有机物和多种形态的重金属离子,一般化学法处理成本高,且不能稳定达标。脉冲电絮凝针对电镀废水重金属破络以及去除COD方面发挥独特的优势,结合后续加载磁絮凝技术,整体工艺占地面积小,COD和重金属的处理效率高。对于车间镀锌、铬、铜等产品排放的综合废水处理有显著的效果,通过本工程应用,出水水质各项指标均达到电镀污染物排放标准(GB21900-2008)表2要求,COD去除率70%以上,六价铬离子、锌离子、铜离子去除率均在99%以上。