Increase Of Magnetic Flux Density Research Articles

Mechanism of magnetic field condition on deformation behavior of sheet metal using a property-adjustable flexible-die

To provide intelligent control options during sheet metal forming process, magnetorheological (MR) fluid has been applied as a property-adjustable flexible-die. However, the mechanism of the magnetic field effect on the sheet deformation behavior is not clear yet. In this paper, to clarify the deformation mechanism, the bulging behavior of thin-walled Al1060-O sheet was systematically investigated through experiment and numerical simulation. Special attention was paid to the effect of magnetic field on loading curve, bulge dome height, and thickness strain distribution. Results showed that the maximum bulging force increased obviously with the increase of magnetic flux density. The bulge dome height and thickness strain were influenced by magnetic field condition and magnetic particle content synthetically. Appropriate magnetic field condition and magnetic particle content can improve formability. However, excessive magnetic flux intensity and magnetic particle volume fraction, for example, B = 0.20 T and φ = 46%, would lead to premature rupture. Finite element analysis was adopted to assist in explaining the bulging behavior. Detailed analysis indicated that the flow stress variations caused by magnetic field affect the stress states, velocity distribution of MR fluid, and sheet/MR fluid contact condition, further leading to different stress and strain distribution of sheet metal. Finally it causes the great difference in specimen geometry and wall thickness distribution.

Femtosecond laser layered ring trepanning of stainless steel sheets with and without transverse magnetic assistance

A novel femtosecond laser layered ring trepanning (LLRT) technology assisted by external transverse magnetic fields is reported for improving laser trepanning efficiency and quality while reducing hole defects. The influence of key operating parameters on blind-hole geometry trepanned by altering magnetic flux density was discussed. The element compositions were compared and analyzed for the corresponding domains near the entrances, middles and bottoms of the blind-hole sidewalls trepanned with and without magnetic assistance. The surface morphology and roughness together with local microscale irregularities and defects of the blind-hole sidewalls trepanned with and without magnetic assistance were also analyzed based on corresponding comparisons via altering scanning speed, magnetic flux density, pulse repetition rate and feed distance. It was demonstrated that the magnetic field-enhanced plasma motion induced by Lorentz force scoured hole sidewall and weakened the multi-shock effect on the hole wall. A stronger transverse magnetic field was more effective to reduce/avoid the local hole-wall defects such as micro cracks together with micro irregularities for improving the formation uniformity/quality of the hole wall. With the increase of magnetic flux density, the hole depth and aspect ratio increased while the hole diameter and taper angle decreased. A smaller feed distance was more helpful for reducing hole-wall surface roughness, while the addition of an external magnetic field was useful for weakening hole-wall oxidation. The oxidation difference of the oxidized layers on the hole wall mainly resulted from the transient uncertainty/instability of further oxidation, which was caused by the thermal multi-shock effect induced by the transiently-changeable motion of laser-induced plasma at a high temperature. Despite the uncertainty normally encountered during the complex LLRT process, it was indicated that the repeatability of this work was acceptable based on the repeated experiments and measurements.

Thermal and exergy efficiency of magnetohydrodynamic Fe3O4‐H2O nanofluids flowing through a built‐in twisted turbulator corrugated tube under magnetic field

AbstractExperimental investigations were conducted to explore the thermal and exergy efficiency of Fe3O4‐H2O nanofluids in a corrugated tube. Some influences of the twisted turbulator, horizontal magnetic fields (B = 6mT, 12mT, and 18mT), particle mass fractions (ω = 0.1, 0.3, and 0.5 wt%) as well as Re numbers (800–12,000) were analyzed. The experimental results exhibited that the heat transfer capacity of nanofluids intensifies with the increment of mass fraction but weakens with the increase of magnetic flux density. For the same external conditions, the heat transfer capability of the corrugated tube with an inserted twisted turbulator is obviously stronger than that without the turbulator. The resistance coefficient can be augmented by the increasing mass fraction and horizontal magnetic field. In addition, the thermal efficiency R3 and the exergy efficiency were adopted to estimate the comprehensive performance of each working condition. It could be found that the increased mass fraction and reduced magnetic flux density cause an increasing trend on the thermal efficiency. Also, it was obtained that the exergy efficiency of working fluids is intensified under identical pumping power.

High performance of methanol gas sensing of ZnO/PAni nanocomposites synthesized under different magnetic field

The gas sensing performance of ZnO thin film was enhanced by polyaniline (PAni) composite, which was deposited on the thin film under different magnetic flux density (0.0, 0.3, and 0.5 T). X-ray diffraction (XRD) patterns, Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) results indicated that the heterostructures were created by ZnO thin film and PAni composites. The XRD and XPS results showed that different magnetic field caused the changes in structure and chemical bondings of the PAni composites. Scanning electron microscopy (SEM) images showed that the grain size of the PAni composites was also affected by the different magnetic field intensity. Gas sensing measurements of the samples indicated that the operating temperature of the sensors to sense methanol vapor was decreased from 150 °C for the gas-sensing device-based pristine ZnO thin film to 60 °C for the gas-sensing device-based ZnO/PAni composite, which was synthesized under 0.5 T of the magnetic flux density. In addition, the sensor response was increased by the increase of magnetic flux density. Furthermore, ZnO/PAni composite, which was formed by 0.5 T of magnetic flux density, performed a good selectivity compared to the other samples. In fact, characterization and gas sensing measurements indicated the protonation and deprotonation process of ZnO/PAni as well as lower activation energy play two essential roles in the enhancement of the gas sensing performance.

Field-Winding Claw-Pole Type Motor Characteristics Analysis Using Additional Ferrite Magnets

The magnetic flux density of a rotor core is increased on the basis of the B-H characteristics of the core when the field current of a field-winding claw-pole type motor (FWCPM) is increased. However, owing to the saturation of the rotor core caused by the increase in magnetic flux density, the magnitude of the electromotive force relative to the field current increase in a nonlinear direction. Therefore, to improve the performance of the FWCPM, it is necessary to reduce the leakage flux and rearrange the source of the rotor in order to supply additional magnetic flux. In this paper, three types of ferrite assisted field-winding claw-pole type motors (FAFWCPM) are proposed to improve the nonlinearity and performance of the FWCPM field current. The magnets applied to the FAFWCPM are located between the claws, at the front of the claws, and at the tops and bottoms of the claws. Further, to ensure analytical accuracy, the amount of magnets used in the motor is equally limited. Finally, the magnitude of the electromotive force under a no-load condition and the average torque under the load condition are studied through three-dimensional finite element analysis.

High magnetic-field-induced solute interception among dendrite arms in the mushy zone of a Mn–Sb alloy

The effect of high magnetic fields on the solute diffusion behavior in the mushy zone of a Mn–Sb alloy has been investigated. A hypoeutectic Mn–Sb alloy was heated in high magnetic fields to yield a mixture of primary MnSb dendrites and Mn/Sb liquid to simulate the mushy state, annealed isothermally for various times, and quenched to room temperature. Without a magnetic field or with a 1-T field, the quenched alloy had a microstructure that was composed of MnSb particles that were dispersed in MnSb/Sb eutectics. At higher magnetic fields, a multiple-phase mixed microstructure that consisted of fine MnSb particles, bulk Sb, and MnSb dendrites and eutectic was observed at relatively short annealing times. The amounts of fine MnSb particles and bulk Sb decreased with an increase in annealing time but increased with an increase in magnetic-flux density. The appearance of the multiple-phase mixed microstructure can be attributed to solute interception in the mushy zone, which can change the solute distribution among the dendrite arms and which is caused by a high magnetic field that is based on the Lorentz force. The application of a high magnetic field to the mushy state of the alloys is proposed as an effective route for the in-situ control of solute diffusion in the mushy zone.

Performance Analysis of Heaving Float Wave Energy Converter with Liquid Metal MHD Generator

Heaving float wave energy converter/conversion (WEC), which makes use of liquid metal magnetohydrodynamics (LMMHD) generator, converts directly the linear motion of heaving float into electrical power. In this paper, effect of magnetic flux density on performance of heaving float LMMHD-WEC is analytically investigated. The results reveal that the capture width ratio, the load voltage, the output power, the system efficiency have maximum values with the increase of magnetic flux density.

Micro-magnetofluidics of ferrofluid droplet formation in a T-junction

The combination of microfluidics with magnetism has led to the emergence of a new scientific domain known as micro-magnetofluidics. The present study aims to investigate the interfacial dynamics of ferrofluid droplet formation under magnetic field in a microfluidic T-junction. A non-uniform magnetic field was constructed by placing a permanent magnet at one side of the T-junction. Three typical flow regimes including the slug, slug-dripping transition and dripping flow were observed. The external magnetic field promotes the transition from the slug-dripping transition flow to the slug flow, prolongs the generation cycle of ferrofluid droplets and hinders the ferrofluid droplet formation. As the magnetic flux density increases, both the increasing rate of the length for the thread tip and the expanding rate of the dispersed neck decrease, and the peak value of the minimum width of the dispersed neck increases. The ferrofluid droplet size increases with increasing the magnetic flux density while decreases with increasing the two-phase flow rate ratio and the capillary number. A scaling law is proposed to predict the size of ferrofluid droplets, by taking the two-phase flow rate ratio, capillary number and magnetic Bond number into account.

Magnetic-field-assisted fabrication of micro-convex domes using long pulse laser

Surfaces with mimic micro-convex domes offer superior functions such as superhydrophobicity, self-cleaning, anti-wear and drag reduction. In this paper, magnetic-filed-assisted laser surface texturing (LST) using long pulse laser was employed to create micro-convex domes on 304L stainless steel. Spherical cap shaped domes with ripples around the bottom were fabricated through LST. The effects of laser power and magnetic flux density on surface morphologies of the created convex domes were investigated. It was found that the height and diameter of the created convex dome increased with the increment of the laser power without magnetic field. Moreover, the height of the created convex dome grew up gradually with the increase of magnetic flux density due to the induced Lorentz force. The height of the convex dome was increased by as much as 14.5% as compared to LST without the applied magnetic field at a laser power of 54 W. However, the applied magnetic field had no evident effect on the diameter of the created convex dome.

Refinement of primary Si in the bulk solidified Al-20 wt.%Si alloy assisting by high static magnetic field and phosphorus addition

Effects of high static magnetic field (HSMF) on microstructures and solidification process of Al-20 wt.%Si alloys with and without phosphorus addition (P addition) have been investigated. The size of primary Si (SPS) is refined continuously as the increase of magnetic flux density (B), and the minimum SPS value is about 15.4 μm when B is 29 T without P addition. However, the SPS decreases firstly and then increases as the increasing B combined with P addition, the average SPS value reaches to the minimum about 21.1 μm when B is 1 T. A unified refinement mechanism has been suggested based on the theory of thermodynamic nucleation and kinetic growth under the HSMF. And the influence of P addition on the morphology of primary Si has also been discussed.

Characteristics of welding and arc pressure in TIG narrow gap welding using novel magnetic arc oscillation

Tungsten inert gas (TIG) narrow gap welding using magnetic arc oscillation is one of the most important methods for joining thick components. Today’s developments are aimed at increasing a sophisticated process understanding, especially concerning the physical effect of arc behavior, which can provide many strategies to enhance weld prediction and joint quality. In this article, the arc behaviors studied by its arc pressure, static characteristic, and arc profile in terms of arc force are presented. With the help of the forces acting on the welding arc, arc profile can be considered separately to allow an improved investigation of narrow gap welding involved. Measurements of arc pressure distribution are used to validate the weld formation and the final welding result. Under the same conditions, the uniformity of arc pressure distribution in both the bottom and sidewall improved with the increase in magnetic flux density. Furthermore, a comparative study of arc static characteristic with magnetic field and non-magnetic field has also been carried out. The reduction in the difference of arc static characteristic is attributed to the inverse effect between electromagnetic pinch force and Lorentz force with the increasing welding current.

Optimization of Magneto-Rheological Damper for Maximizing Magnetic Flux Density in the Fluid Flow Gap Through FEA and GA Approaches

A magneto rheological (MR) fluid damper offers cost effective solution for semiactive vibration control in an automobile suspension. The performance of MR damper is significantly depends on the electromagnetic circuit incorporated into it. The force developed by MR fluid damper is highly influenced by the magnetic flux density induced in the fluid flow gap. In the present work, optimization of electromagnetic circuit of an MR damper is discussed in order to maximize the magnetic flux density. The optimization procedure was proposed by genetic algorithm and design of experiments techniques. The result shows that the fluid flow gap size less than 1.12 mm cause significant increase of magnetic flux density.

Effect of Axial Magnetic Field on the Microstructure and Mechanical Properties of CrN Films Deposited by Arc Ion Plating

CrN films were deposited on the high-speed-steel substrates by arc ion plating. The effect of an axial magnetic field on the microstructure and mechanical properties was investigated. The chemical composition, microstructure, surface morphology, surface roughness, hardness and film/substrate adhesion of the film were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope (SEM), surface morphology analyzer, Vickers microhardness test and scratch test. The results showed that the magnetic field puts much effect on the microstructure, chemical composition, hardness and film/substrate adhesion of the CrN films. The N content increases and Cr content decreases when the magnetic flux density increases from 0 to 30 mT. All of the CrN films were found to be sub-stoichiometric. With an increase in the magnetic flux density, the film structures change in such way: Cr2N → Cr2N + CrN → CrN + Cr2N → CrN. The SEM results showed that the number of macroparticles (MPs) on the film surface is significantly reduced when the magnetic flux density increases to 10 mT or higher. The surface roughness decreases with the magnetic field, which is attributed to the fewer MPs and sputtered craters on the film surface. The hardness value increases from 2074 HV0.025 at 0 mT (without magnetic field) and reaches a maximum value of 2509 HV0.025 at 10 mT. The further increase in the magnetic flux density leads to a decrease in the film hardness. The critical load of film/substrate adhesion shows a monotonous increase with the increase in magnetic flux density.

Enhancement of Salt Uptake with the Application of Rotary Magnetic Field in Brining Cucumber

<p>An experimental system by use of magnetic and hydrodynamic force was established to accelerate mass transport and thus to shorten the salting equilibrium time in salting of fresh-cut cucumbers. The cucumbers were brined with flowing 3% NaCl solution under rotary magnetic field at 22 ºC. During brining period, salt contents of the cucumbers at varying Reynolds number of flowing brine, rotary frequency, and magnetic flux density of magnetic field were separately investigated and the salt uptake kinetics was also analyzed. Results showed that flowing brine disturbed the salt diffusion into cucumber tissues without the application of magnetic field. Consequently, the salt uptake rate decreased compared to the conventional brining. No significant difference in salt content of cucumbers was observed between the conventional brining and static-magnetic-field-assisted brining. The salt uptake rate was improved by the combination of rotary magnetic field and flowing brine. The increment of salt uptake rate during this combined treatment got larger with the increase of magnetic flux density. Salt uptake rate of cucumber increased with the increase of rotational frequency of the magnetic field and Reynolds number of the flowing brine, up to a critical value. A 170% increment in salt uptake rate constant could be achieved at magnetic flux density 0.13 T, rotational frequency 5 Hz and Reynolds number 1127. Thus, an intergrated technique based upon rotary magnetic field and flowing brine is provided for brining of porous agricultural products.</p>

Tailoring the Morphology, Structure and Magnetic Properties of Electrodeposited CoFe Films onto Si(100) by In-Situ Uniform and Gradient High Magnetic Fields

In this work uniform high magnetic field of up to 12 tesla and well-defined magnetic field gradients were in-situ applied during the electrodeposition process of CoFe alloy films on Si(100) substrate with Ni seed-layer. The evolution of morphology obtained by LSCM and AFM revealed that the electrodeposition under uniform or gradient magnetic fields provides advantage of forming high quality films with small grains size and low surface roughness. The X-ray diffraction measurements revealed that the crystalline structure of the films changed with the increase of magnetic flux density from face-centered cubic (fcc) at 0 T to body-centered cubic (bcc) at 12 T. However, the formation of a mixture phase (fcc+bcc) under gradient magnetic fields reflected a negative effect of the field gradient force on the transformation from fcc phase to bcc phase. With increasing magnetic flux density (B), the saturation magnetization (Ms) and coercive force (Hc) of the films increased, while in the case of B = 12 T, both of Ms and Hc decreased. It could be ascribed to the changes in the chemical composition and the formation of the mixture phases, due to the combined effects of the paramagnetic force, micro-MHD and the field gradient force under different magnetic field conditions.

Design and Test Performance of 2G Pancake Coils for HTS DC Induction Heater Prototype

To improve the poor efficiency of the conventional induction heater using copper coil, a high temperature superconducting (HTS) DC induction heater is considered. In this study, we designed and built an HTS DC induction heater prototype with an iron core, and tested the insulated and no-insulation (NI) double pancake coils (DPCs). The results show that the critical currents of the DPCs with the iron core somewhat decrease than those without the iron core. The V-I curve of the insulated coil is a standard one of the superconductor, but a linear voltage appears in the NI coil due to the contact resistance between neighboring wires. For the insulated coil, the magnetic flux density of the air core is proportional to the coil current. However, a charging delay is found in the NI coil: The increment of the magnetic flux density for the NI coil is negligible when the current is increasing at first. Then the magnetic flux density increases and finally saturates even if the current is stable. The inductance of the coil with the iron core is about six times of that without the iron core.

Influence of magnetic field on the nucleation rate control of mono paracetamol

Crystallization of paracetamol was carried out under magnetic field in pure aqueous solution at ambient condition for the first time. Solutions at different supersaturation levels σ = 0.28–1.6 were exposed to various magnetic flux densities in the range 160–510 Gauss and the grown crystals were compared with that grown in the absence of magnetic field. Both in the absence and presence of magnetic field, solution yields only stable mono paracetamol and does not favors the metastable ortho polymorph at all supersaturation levels. The presence of magnetic field reduces the rate of crystal nucleations as well as modifies the habit of the nucleated mono paracetamol. Crystals obtained in the presence of magnetic field were of good quality and highly transparent as compared to the crystals grown in the absence of magnetic field. The induction period of the nucleation in solution decreases significantly with increase in magnetic flux density at all supersaturation ranges. The internal structure and thermal stability of the grown paracetamol crystal was confirmed by PXRD and DSC analysis.

Magnetostriction Increase of Tb0.3Dy0.7Fe1.95 Alloy Prepared by Solidification in High Magnetic Fields**Supported by the National Natural Science Foundation of China under Grant Nos 51425401 and 51271056, the Fundamental Research Funds for the Central Universities under Grant Nos N140901001 and N140902001, and the Doctoral Scientific Research Foundation of Liaoning Province under Grant No 20131034.

Tb0.3Dy0.7Fe1.95 alloys are solidified under various high magnetic field conditions. The influence of a high magnetic field on the crystal orientation, morphology and magnetostriction of the alloys are studied. The results show that with the increase of magnetic flux density, the crystal orientation of the (Tb,Dy)Fe2 phase changed from 〈113〉 to 〈111〉 direction; the grains in the alloys tended to align along the magnetic field direction; and the magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is remarkably improved. The change in magnetostriction of Tb0.3Dy0.7Fe1.95 alloys is linked to the amount and the crystal orientation behavior of the (Tb,Dy)Fe2 phase.

Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

Utilizing ANSYS CFX commercial software and volume fraction of fluid (VOF) model, fluctuation behavior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided into three zones: frontal valley zone, back valley zone and horizontal zone; as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag interface fluctuation can be properly controlled and slag entrapment can be prevented.

Effect of rotating magnetic field on the fading effect of Al–5Ti–1B in commercial pure Al

Abstract