Stabilization of fluidized beds of particles magnetized by an external field: effects of particle size and field orientation

2013 ◽  
Vol 732 ◽  
pp. 282-303 ◽  
Author(s):  
M. J. Espin ◽  
J. M. Valverde ◽  
M. A. S. Quintanilla
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Magnetic Fields ◽  
Yield Stress ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Magnetic Contribution ◽  
Field Orientation ◽  
Jamming Transition ◽  
The Magnetic Field

AbstractThis paper reports experimental measurements on the yield stress, the permeability to gas flow and the gas velocity at the jamming transition of gas-fluidized beds of magnetizable particles as affected by particle size and orientation and strength of an externally imposed magnetic field. Tested samples consisted of relatively monodisperse magnetite powders of $35$, $50$ and $65~\unicode[.5,0][STIXGeneral,Times]{x03BC} \mathrm{m} $ particle size. The permeability to gas flow and jamming transition velocity increase with particle size and in a specially marked way when the magnetic field is applied along the gas flow direction. The magnetic contribution to the yield stress is also particularly enhanced for co-flow magnetic fields. However, the effect of particle size on the yield stress shows a dependence on the microstructure packing as affected by particle size and orientation of the field. The magnetic yield stress increases with particle size for magnetic fields applied in the cross-flow configuration while the opposite trend is observed when the direction of the magnetic field is parallel to the gas flow. The observations reported in this paper are generally explained by the formation of chains of particles due to attractive magnetic forces between the magnetized particles and the orientation of these chains with respect to the magnetic field.

Stabilization of gas-fluidized beds of magnetic powders by a cross-flow magnetic field

2011 ◽  
Vol 680 ◽  
pp. 80-113 ◽  
Author(s):  
M. J. ESPIN ◽  
J. M. VALVERDE ◽  
M. A. S. QUINTANILLA ◽  
A. CASTELLANOS
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Yield Stress ◽  
Material Properties ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Cross Flow ◽  
Gas Velocity ◽  
Gas Fluidized Beds ◽  
The Magnetic Field

In this paper we present an experimental study of the stabilization of gas-fluidized beds of magnetic powders by application of a cross-flow magnetic field. The powders tested consist of magnetite and steel powders in a range of particle size dp between 35 and 110 μm, allowing us to investigate the effect of particle size and material properties on magnetic stabilization. In the operation mode employed by us the magnetic field is applied to the unstable bubbling bed and the gas velocity is slowly decreased. According to our observations, the bed is stabilized at a critical gas velocity by the jamming of particle chains formed during bubbling because of the attractive forces induced between the magnetized particles, which are thus responsible for stabilization. Although the magnetic field is applied in the horizontal direction, these chains are mechanically stable at orientations close to the gas flow direction, in agreement with the prediction of an unconfined chain model based on the balance between gas flow shear and interparticle magnetic force fm. Since fm is increased as dp is increased, the critical gas velocity at marginal stability vc for a fixed field strength B is seen to increase with dp. As the gas velocity v0 is decreased below vc, there is a rearrangement of the structure depending on particle size. Restructuring of the bed depends on particle size as derived from measurements of its permeability to the gas flow, which causes the yield stress to be a function of particle size. It is also inferred from our results that natural agglomeration of fine particles (in the absence of a magnetic field) due to van der Waals forces enhances the yield stress of the magnetically stabilized bed. From our experimental results it is concluded that structural effects, as affected by operating conditions and material properties, play a main role in the rheology of the stabilized magnetofluidized bed (MFB).

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

Monte Carlo investigation of electron fluence perturbation in MRI-guided radiotherapy beams using six commercial radiation detectors

2022 ◽  
Author(s):  
Yunuen Cervantes ◽  
Simon Duane ◽  
Hugo Bouchard
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Solid State ◽  
Magnetic Fields ◽  
Radiation Detectors ◽  
Detector Response ◽  
Field Orientation ◽  
Solid State Detector ◽  
Parallel Orientation ◽  
The Magnetic Field

Abstract With the integration of MRI-linacs to the clinical workflow, the understanding and characterization of detector response in reference dosimetry in magnetic fields are required. The magnetic field perturbs the electron fluence (Fe), and the degree of perturbation depends on the irradiation conditions and the detector type. This work evaluates the magnetic field impact on the electron fluence spectra in several detectors to provide a deeper understanding of detector response in these conditions. Monte Carlo calculations of Fe are performed in six detectors (solid-state: PTW60012 and PTW60019, ionization chambers: PTW30013, PTW31010, PTW31021, and PTW31022) placed in water and irradiated by an Elekta Unity 7 MV FFF photon beam with small and reference fields, at 0 T and 1.5 T. Three chamber-axis orientations are investigated: parallel or perpendicular (two possibilities: FL towards the stem or the tip) to the magnetic field and perpendicular to the beam. One orientation for the solid-state detector is studied: parallel to the beam and perpendicular to the magnetic field. Additionally, Fe spectra are calculated in modified detector geometries to identify the underlying physical mechanisms behind the fluence perturbations. The total Fe is reduced up to 1.24% in the farmer chamber, at 1.5 T, in the parallel orientation. The interplay between the gyration radius and the farmer chamber cavity length significantly affects Fe in the perpendicular orientation; the total fluence varies up to 5.12% in magnetic fields. For the small-cavity chambers, the maximal variation in total Fe is 0.19%, for the reference field, in the parallel orientation. . In contrast, significant small-field effects occur; the total Fe is reduced between 9.86% to 14.50% at 1.5T (with respect to 0T) depending on the orientation. The magnetic field strongly impacted the solid-state detectors in both field sizes, probably due to the high-density extracameral components. The maximal reductions of total Fe are 15.06±0.09% (silicon) and 16.00±0.07% (microDiamond). This work provides insights into detector response in magnetic fields by illustrating the interplay between several factors causing dosimetric perturbation effects: 1) chamber and magnetic field orientation, 2) cavity size and shape, 3) extracameral components, 4) air gaps and their asymmetry, 5) electron energy. Low-energy electron trajectories are more susceptible to change in magnetic fields, and generally, they are associated with detector response perturbation.

scholarly journals Magnetic-Field-Orientation Dependent Magnetoelectric Effect in FeBSiC/PZT/FeBSiC Composites

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Jun-Xian Ye ◽  
Jia-Mian Hu ◽  
Zhan Shi ◽  
Zheng Li ◽  
Yang Shen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetoelectric Effect ◽  
Experimental Measurements ◽  
Bias Magnetic Field ◽  
Field Orientation ◽  
Magnetic Field Orientation ◽  
Field Dependent ◽  
Simulation Results ◽  
The Magnetic Field

We investigate the magnetic-field-orientation dependent magnetoelectric (ME) effect in the FeBSiC/Pb(Zr,Ti)O3(PZT)/FeBSiC laminates. It is shown that, by only using the bias-magnetic-field dependent ME response measured with the magnetic-field parallel to the surface plane of PZT slab, the magnetic-field-orientation dependent ME coefficient upon magnetic-fields of various amplitudes can be obtained via computer simulations. The simulation results match well the experimental measurements, demonstrating the applicability of the ME laminates-based sensors in detecting magnetic-fields with uncertain amplitudes and/or orientations in environment.

scholarly journals Magnetotransport studies of Fe vacancy-ordered Fe4+δSe5nanowires

2020 ◽  
Vol 117 (23) ◽  
pp. 12606-12610
Author(s):  
Keng-Yu Yeh ◽  
Tung-Sheng Lo ◽  
Phillip M. Wu ◽  
Kuei-Shu Chang-Liao ◽  
Ming-Jye Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electrical Transport ◽  
Parent Phase ◽  
Mixed Valence ◽  
Field Orientation ◽  
Spin Orbital ◽  
Field Independent ◽  
Mi Transition ◽  
The Magnetic Field

We studied the electrical transport of Fe4+δSe5single-crystal nanowires exhibiting √5 × √5 Fe-vacancy order and mixed valence of Fe. Fe4+δSe5compound has been identified as the parent phase of FeSe superconductor. A first-order metal-insulator (MI) transition of transition temperatureTMI∼ 28 K is observed at zero magnetic fields (B). Colossal positive magnetoresistance emerges, resulting from the magnetic field-dependent MI transition.TMIdemonstrates anisotropic magnetic field dependence with the preferred orientation along thecaxis. At temperatureT< ∼17 K, the state of near-magnetic field-independent resistance, which is due to spin polarized even at zero fields, preserves under magnetic fields up toB= 9 T. The Arrhenius law shift of the transition on the source-drain frequency dependence reveals that it is a nonoxide compound with the Verwey-like electronic correlation. The observation of the magnetic field-independent magnetoresistance at low temperature suggests it is in a charge-ordered state belowT∼ 17 K. The results of the field orientation measurements indicate that the spin-orbital coupling is crucial in √5 × √5 Fe vacancy-ordered Fe4+δSe5at low temperatures. Our findings provide valuable information to better understand the orbital nature and the interplay between the MI transition and superconductivity in FeSe-based materials.

Magneto-Stabilization of Fluidized Beds as due to Short Ranged Interparticle Forces

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
M. J. Espin ◽  
Jose Manuel Valverde ◽  
M. A S. Quintanilla
Keyword(s):  
Particle Size ◽  
Yield Stress ◽  
Fluidized Beds ◽  
Gas Flow ◽  
Fine Particles ◽  
Marginal Stability ◽  
Chain Model ◽  
Gas Velocity ◽  
Interparticle Forces ◽  
Magnetic Stabilization

We present an experimental study on the stabilization of bubbling gas-fluidized beds of magnetic powders by interparticle forces induced by an externally applied magnetic field in the cross-flow configuration. The samples tested consist of magnetite and steel powders in a range of particle size dp between 35 and 110 microns, allowing us to investigate the effect of particle size and material properties on magnetic stabilization. According to our observations, the stabilization physical mechanism is ruled by the jamming of particle chains created due to attractive forces induced between the magnetized particles. Even in the case of the horizontally applied field, these chains are mechanically stable at orientations close to the gas flow direction in agreement with the prediction of a chain model based on the balance between gas flow shear and interparticle magnetic force fm. Since fm is increased as dp is increased, the critical gas velocity at marginal stability vc for a fixed field strength B is seen to increase with dp. The yield stress of the stabilized bed s increases steadily as the gas velocity v0 is decreased below vc. Thus, s is increased with dp for fixed v0 and B. It is inferred also from our results that natural aggregation of fine particles due to the universal van der Waals interaction enhances the yield stress of the magnetically stabilized bed. A main conclusion is that interparticle short ranged attractive forces play an essential role on magnetic stabilization of fluidized beds.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust &amp; Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust &amp; Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

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