An Experimental Study of a Bubble-Driven Liquid Metal Flow Under the Influence of a Rotating Magnetic Field

In this study we investigate the flow structure in a liquid metal cylinder while a bubble-driven flow is superposed with a rotating magnetic field(RMF).Argon gas is injected through a nozzle into a column of the eutectic alloy GalnSn.Without electromagnetic stirring the bubble plume in the centre region of the cylindrical vessel produces a recirculation with high velocities near the free surface while the fluid velocities in the bottom region remain rather low.The measurements revealed the potential of the RMF to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume.Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.     

Electromagnetic Separation of Nonmetallic Inclusions From Liquid Steel by High Frequency Magnetic Field

The currernt work is to investigate the removal of nonmetallic inclusionsfrom liquid steel using electromagnetic separation.In experiments,a certain amount of aluminum was added to the molten steel in a crucible to generate aluminum inclusions.A layer of aluminum clusters were observed close to the wall of the crucible.Three dimensional electromagnetic field and fluid flow simulation indicated that particles moved to the wall of the crucible by the EM force and were entrapped at the inside wall of the crucible.     

Liquid Metal Stirring in a Rectangular Cavity Generated by the Traveling Magnetic Field

This study examines the flow generated in a rectangular cavity by the traveling magnetic field and the transport of passive admixtures in the molten metal,as well as the effects of various parameters and parameter combinations on the flow intensity and admixture distribution.The focus of the paper is on mathematical modeling and experimental investigation of the processes of admixture homogenization in the bulk of liquid metal subjected to electromagnetic stirring.The obtained results can further be used to determine the optimal conditions for manufacture of high-quality alloys and to select the appropriate stirring process parameters.     

Oscillation Characteristics of Molten Metal Free Surface Under Compound Magnetic Field

  The free surface waves of a molten low melting point Sn 32%Pb 52%Bi alloy under the imposition of an AC and a static magnetic field were visualized and recorded by use of a laser displacement sensor and a high speed video camera. The Fourier analysis method was used to analyze the oscillation characteristics. The results show that at the center of the free surface, the azimuthal and radial oscillation mode can be found simultaneously owing to AC magnetic field. With increasing coil current intensity, the amplitude and the main frequencies of the oscillations increase, and the azimuthal fluctuation at the center of the free surface is also enhanced. The fluctuation characteristics are closely related to the turbulent flow induced by the alternating electromagnetic force. A series of regular traveling waves can be observed on free surface, and the main frequencies of oscillations at three phase points decrease owing to superposing AC and static magnetic field. The static magnetic field can remarkably control the unstable swinging behavior of free surface. With increasing static magnetic flux density, the amplitude of oscillations at the center of free surface decreases firstly, and then increases, but the fluctuation amplitude at the triple phase point always reduces and keeps within 1 mm, and the azimuthal waves at the center of free surface are weakened. Especially at 144 T, the radial waves are dominant. The static magnetic flux density should be controlled in an appropriate range to obtain more stable free surface. With compound magnetic field, even if the static magnetic flux density is above 10 T, the free surface still vibrates with lower amplitude and dominant frequency.     

Liquid Metal Heat Transfer in an Inclined Tube Affected by a Longitudinal Magnetic Field

This paper presents results of hydrodynamic and heat transfer investigations in liquid metal flow affected by a longitudinal magnetic field in an inclined tube with respect to tokamak cooling problem.Experimental study has been conducted for the tube with slope 15 to the horizon which corresponds to the conditions oflTER project in case the LM flow faced longitudinal MF.The results obtained in the regimes without the MF,may be interesting for the design of nuclear reactors cooled by LM and metallurgical processes.     

Intermittent Behavior Caused by Surface Oxidation in a Liquid Metal Flow Driven by a Rotating Magnetic Field

The focus of the experimental and numerical study presented in this article is on the bulk flow within a swirling liquid metal column driven by a rotating magnetic field (RMF), whereas the free surface of the melt was covered by a distinct oxide layer. Flow measurements revealed an anomalous behavior of the flow: Pronounced oscillations of both the primary swirling and the secondary recirculating flow occur spontaneously. This peculiarity can be attributed to the influence of the oxide layer at the surface of the metal. The motion of the covering layer is governed by the strength of the fluid flow and the properties of the layer, and it might exhibit three different states of motion: permanent rotation, intermittent rotation, or the quiescent state. The regime of an intermittent oxide layer rotation reveals a striking influence on the bulk flow of the liquid metal. The amplitude of the velocity oscillations observed seems to be at least one order of magnitude larger than those of turbulent fluctuations in a steady RMF-driven flow. The essential features of the phenomenon observed were reproduced by a simple numerical model.     

Inertial Waves Occurring in a Liquid Metal Column due to Pulsed Excitation by a Rotating Magnetic Field

We present an experimental study concerning the flow inside a liquid metal column exposed to a pulsed rotating magnetic field.This paper is aimed at highly resolved,quantitative velocity measurements in the eutectic GalnSn alloy.A novel ultrasound Doppler system was used two measure two-dimensional velocity fields of the secondary flow in the radial-meridional plane.It employs an array of 25 transducer elements allowing a fast electronic traversing with concurrently high spatial and temporal resolution.The measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex structures.The results demonstrate that the arising flow structure depends sensitively on the frequency of the RMF pulses.A maximum intensity of a periodic meridional flow can be observed,if the corresponding pulse frequency fp relates to the eigenperiod of the respective inertial mode in a developed regime.The electromagnetic stirring method that uses a modulated RMF offers considerable potential to enhance the stirring efficiency and to optimize the properties of castings by a well-aimed flow control during solidification.     

The Impact of a Vertically Travelling Magnetic Field on the Flow in a Cylindrical Liquid Metal Bubble Plume

This article describes laboratory experiments for the investigations of flow structures and related transport processes in liquid metal bubbly flows under the influence of a traveling magnetic field (TMF). The melt flow is driven by central gas injection into a cylindrical container filled with the low-melting-point alloy GaInSn. The velocity fields of both the liquid and the gaseous phase were measured nonintrusively using the ultrasound Doppler method. Depending on the traveling direction of the magnetic field, the TMF mainly imposes either a concurrent flow or counterflow with respect to the original bubble-driven circulation. In general, the application of a downward TMF significantly increases the liquid velocity all over the fluid volume. An upward TMF gives rise to the more complex structures of the velocity field resulting in alternately arranged upstream and downstream regions. Both the upward and downward TMF promote the occurrence of nonsteady motions with distinct velocity fluctuations leading to an intensification of related transport processes in the melt and providing the perspective of enhanced mixing efficiencies.     

Hydrothermal Synthesis of Nano Ba-Ferrite With Additional High Pressure Under the Magnetic Field

The pressure of hydrothermal system is increased based on the traditional hydrothermal synthesis to prepare nano-barium ferrite at the reaction temperature of 180℃under different magnetic field.Using XRD,SEM and TEM methods,the phase composition and micro structure of the nano-barium ferrite powder obtained under different initial pressure（l.0atm,1.5atm and 2.0atm）is discussed.All the powder prepared under different initial pressure is mainly composed of BaFei₂O₁₉.But the morphology of the products is different.Flake BaFe₁₂O₁₉is obtained under the 10T magnetic field when the initial pressure is 1.5atm and 2.0atm.Moreover,the degree of crystallinity of hydrothermal products is also improved by the application of magnetic field and additional high pressure.Hexagonal flake grains of BaFei₂O₁₉with excellent crystallization have been prepared under 6T magnetic field,when the initial pressure reached2.0atm,some of the rod-like BaFe₁₂O₁₉self-organized to form ordered forked structure through oriented attachment due to the multiple influence of pressure and magnetic field on crystal face energy.It can be found that the additional high pressure will disturb the influence of the magnetic field on one-dimensional growth.And the phenomenon of oriented attachment can be regarded as the intermediate state between the one-dimensional rod and two-dimensional sheet.     

Formation Mechanism of Stray Grain of Nickel-Based Single-Crystal Superalloy Under a High Magnetic Field During Directional Solidification

Metallurgical and Materials Transactions B - We investigate the formation mechanism of stray grain of nickel-based single-crystal superalloy under a high magnetic field. It was shown that the high...     

圆坯电磁软接触连铸结晶器高频磁场分布

通过实验检测和数值模拟方法研究圆坯电磁结晶器切缝形式、切缝宽度、切缝数量及切缝长度对圆坯电磁软接触结晶器内高频磁场分布的影响,为软接触结晶器优化设计提供磁场理论依据.结果表明:切缝数增加可提高透磁性和均匀性;增大缝宽对透磁性影响不明显,但降低均匀性;缝长只在一定范围内对透磁性有影响.     

Progress in Research of Solidification of Metals Under a Strong Magnetic Field

Solidification of metals under a strong magnetic field is a new area for research.Here,some progress in the area is reviewed along with presentation of the fundamental effects of magnetic field.Focus is paid on the subjects of influence of a magnetic field on kinetics of solidification,instability of S/L interface,crystal growth of monophase alloy,eutectic growth,thermoelectrical magnetic convection and its effects,The core problems which should be investigated deeply and the key parameters needed are discussed.     

Effect of Electromagnetic Frequency on Magnetic Flux Coupling by Traveling Magnetic Field

The effect of frequency on magnetic flux coupling field were analyzed with traveling-wave electromagnetic stirring system using a coupled model of magnetic induction and fluid dynamics.Simulations were performed to investigate the influences of the frequency on magnetic flux density,electromagnetic body force and flow field.The results showed that the magnetic flux density decreased with increasing frequency.The electromagnetic body force wavy moved along the same direction and increased with increasing the frequency when the traveling magnetic field is applied.The core area of the stirring was in the bottom of the alloy melt.A large circulation in the vertical section of the alloy melt can be produced by the electromagnetic body and the maximum flow rate first increased and then decreased with increasing frequency.     

Magnetic Properties of Erbium Gallium Gallate under High Magnetic Field

A theoretical investigation on the magnetic properties of rare-earth Er3+ in Er3 Ga5 O12 was reported. The average magnetic moments(M) for applied magnetic field H parallel to the [001 ], [ 100], [ 110], [ 111 ] direction was studied based on the quantum theory. Temperature dependence of the magnetic properties is analyzed for H applied parallel to the [ 100] and [ 111 ] crystallographic directions. The magnetization decreases with increasing temperature,showing good agreement with thermal effect. A strong anisotropy of the magnetization is found under high magnetic field, but when the magnetic field is small, M and H are proportional.     

Microstructure Refinement of Mg-Gd-Y-Zr Alloy Under Pulsed Magnetic Field

The effects of pulsed magnetic field on the solidified microstructure of Mg-Gd-Y-Zr alloy were investigated.Fine uniform equiaxed grains are acquired in the whole ingot by the pulsed magnetic field treatment,and the average grain size of the as-castφ50 mm and 100φmm ingots is refined to 37μm and 47μm with the pulsed magnetic field.The macrosegregation of solute elements of Mg-Gd-Y-Zr alloy is also reduced by the pulsed magnetic field treatment.Structure refinement is due to the electromagnetic undercooling zone in front of the solid/liquid interface by the magnetic pressure,and reduction of temperature gradient by the vibration of melt resulted from the pulsed magnetic field,which increases the nucleation rate and prohibits dendrite growth.In addition,primaryα-Mg dendrites break into fine crystals,resulting in a refined solidification structure of the magnesium alloys.The Joule heat effect induced in the melt also strengthens the grain refinement effect and the spheroidization of dendrite arms.     

Modification of Solidification Structure Under DC Pulse Magnetic Field

A new process using direct cunent pulsed magnetic field for modification of solidification structure of pure aluminium has been investigated.The experimental results show that the fine equiaxed crystal zone exists at the bottom of ingots with pulse magnetic,and with the increase of rated output current the equiaxed grains are more finer.     

Migration of Paramagnetic Ions in Glass Melts Under Influence of a Magnetic Field

Magnetic forces are widely used to influence the properties of materials.The main focus of recent investigations concerning oxide melts mainly was on the use of Lorentz forces either to mix glass melts to avoid an improved inhomogeneity or to measure the flow of these melts.In the last years also the use of magnetic gradient forces has become an object of research mainly in electrochemistry.On the basis of preliminary investigations the influence of these forces on paramagnetic ions such as Fe²⁺in oxide melts is investigated to examine the potential of magnetic gradient forces as a tool to create defined gradient materials.     

Behavior of Conducting Liquid within an Arc Furnace in a Vertical Magnetic Field

In a vertical magnetic field, bulk electromagnetic forces arise in conducting melt within the bath of a dc arc furnace. As a result, the melt is set in motion. The flow of slag and metal in the furnace bath may lead to effective mixing but may also have negative consequences, such as increased lining wear in the region of the hearth electrode. There has been little research on conductive mixing in the bath of a dc arc furnace. Theoretical concerns include the character of the flow in the bath under the action of magnetic fields of specific magnitude; practical considerations include the lack of simple and reliable sources of magnetic fields. In the present work, the utility of a transparent physical model in studying the flow of conducting liquid in an external vertical magnetic field is investigated. The applicability of the modeling results to processes in the 5-t bath of an industrial dc arc furnace is analyzed. It proves possible in principle to study the flow of conducting melt in external vertical magnetic fields on models based on transparent nonmetallic conducting liquids. The use of an aqueous solution of table salt permits assessment of the liquid velocity at its free surface and close to the hearth electrode by video recording. By physical modeling of the flow of conducting fluid in the bath under the action of an external vertical magnetic field, with different switching sequences of the hearth electrode and different currents in the bath, it is possible to establish the character of the liquid flow when the hearth electrode is at the center of the bath or somewhat displaced. The mean rate of liquid rotation in the horizontal plane is increased when the hearth electrode is at some distance from the bath axis. The strength of the vertical magnetic field producing conductive motion in the metal bath of a 5-t dc arc furnace is estimated: around 5 kA/m.