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).

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.

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.

scholarly journals Study on Fluidization Characteristics of Magnetically Fluidized Beds for Microfine Particles

Minerals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 61
Author(s):  
Yakun Tian ◽  
Shulei Song ◽  
Xuan Xu ◽  
Xinyu Wei ◽  
Shanwen Yan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Fluidized Bed ◽  
Magnetic Field Strength ◽  
Fluidized Beds ◽  
Expansion Rate ◽  
Gas Velocity ◽  
Bed Height ◽  
Bed Expansion ◽  
The Magnetic Field

The bed pressure drop, minimum fluidized gas velocity, bed density, and bed expansion rate are important parameters characterizing the fluidization characteristics of gas-solid fluidized beds. By analyzing these parameters, the advantages and disadvantages of the fluidization state can be known. In this study, experiments were conducted to study the fluidization characteristics of a gas-solid magnetically fluidized bed for microfine particles by changing the magnetic field strength, magnetic field addition sequence, and static bed height. The experimental results show that when the magnetic field strength increased from 0 KA/m to 5 KA/m, the minimum fluidized gas velocity of particles increased from 4.42 cm/s to 10.32 cm/s, while the bed pressure drop first increased and then decreased. When the magnetic field strength is less than 3.4 KA/m, the microfine particles in the bed are mainly acted on by the airflow; while when the magnetic field strength is greater than 3.4 KA/m, the microfine particles are mainly dominated by the magnetic field. The magnetic field addition sequence affects the fluidization quality of microfine particles. The fluidized bed with ‘adding magnetic field first’ shows a more stable fluidization state than ‘adding magnetic field later’. Increasing of the static bed height reduces the bed expansion rate. The bed expansion rate is up to 112.5% at a static bed height of h0 = 40 mm and H = 5 KA/m. This will broaden the range of density regulation of a single magnetic particle and lay the advantage of gas-solid magnetically fluidized bed for microfine particles in the field of separation of fine coal.

scholarly journals Observations of Orion Molecular Cloud with NMA

1994 ◽  
Vol 140 ◽  
pp. 185-189
Author(s):  
Y. Murata ◽  
R. Kawabe ◽  
M. Ishiguro ◽  
K.-I. Morita ◽  
T. Hasegawa ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Molecular Cloud ◽  
Gas Flow ◽  
Position Angle ◽  
Aperture Synthesis ◽  
Width Ratio ◽  
Length Width ◽  
The Magnetic Field

AbstractWe have made aperture synthesis multifield observations of Orion Molecular Cloud-1 (OMC-1) in the CS (J=1-0) line using the Nobeyama Millimeter Array (NMA), and obtained 9” resolution maps over 10’ length. The OMC-1 ridge shows a wiggled structure. The position angle of whole the ridge is ~ 0° - 10°, but ~ 20° - 30°around the clumps. It is possible to make this structure by the magnetic field with a position angle of ~ 150°. We also found filamentary structures in the northwest of Orion-KL, with a length-width ratio of more than 25, which are made by the gas flow from Orion-KL.

Platform Design for Characterizing Shear Force Produced by Magnetized Magnetorheological Fluid

2019 ◽  
Author(s):  
Ping-Hsun Lee ◽  
Jen-Yuan (James) Chang
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Yield Stress ◽  
Flux Density ◽  
Shear Force ◽  
Permanent Magnets ◽  
Magnetic Flux Density ◽  
Finite Element Method Result ◽  
Mr Fluid ◽  
The Magnetic Field

Abstract In this paper we proposed a platform for measuring shear force of magnetorheological (MR) fluid by which the relationship of yield stress and magnetic flux density of specific material can be determined. The device consisted of a rotatable center tube in a frame body and the magnetic field was provided by two blocks of permanent magnets placed oppositely outside the frame body. The magnitude and direction of the magnetic field were manipulated by changing the distance of the two permanent magnets from the frame body and rotating the center tube, respectively. For determining the magnetic field of the device, we adopted an effective method by fitting the FEM (finite element method) result to the measured one and then rebuilt the absent components to approximate the magnetic field, which was hardly to be measured simultaneously as different device setup were required. With the proposed platform and analytical methods, the drawing shear force and the corresponding yield stress contributed by MR fluid could be evaluated in respect to the magnitude and direction of given magnetic flux density with acceptable accuracy for specific designing purposes without a large, complex, and expensive instrument.

Development of a double magnetic circuit yield stress measurement device for magnetorheological fluid

2016 ◽  
Vol 28 (10) ◽  
pp. 1249-1259 ◽  
Author(s):  
Xiang-Fan Wu ◽  
Xing-Ming Xiao ◽  
Zu-Zhi Tian ◽  
Fei Chen ◽  
Jian Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Yield Stress ◽  
Magnetic Circuit ◽  
Stress Measurement ◽  
Magnetorheological Fluid ◽  
High Yield ◽  
Magnetic Field Measurement ◽  
Measurement Device ◽  
Accuracy And Repeatability ◽  
The Magnetic Field

On the basis of shear working mode of magnetorheological fluid, in this article, a novel temperature controllable yield stress measurement device is designed, and the double magnetic circuit structure and the heating structure are proposed. And then, the magnetic field and temperature field of the measurement device are simulated, respectively, by the finite element method. Furthermore, several experiments are carried out to evaluate the magnetic field, measurement precision, and repeatability of the self-designed device. The results indicate that the proposed measurement device has uniform magnetic field distribution and controllable temperature and also has high yield stress testing accuracy and repeatability.

ASTROID CURVES FOR A SYNTHETIC ANTIFERROMAGNETIC STACK IN AN APPLIED MAGNETIC FIELD

2009 ◽  
Vol 23 (20n21) ◽  
pp. 4021-4040
Author(s):  
D. M. FORRESTER ◽  
E. KOVACS ◽  
K. E. KÜRTEN ◽  
F. V. KUSMARTSEV
Keyword(s):  
Magnetic Field ◽  
Applied Magnetic Field ◽  
Single Particle ◽  
Material Properties ◽  
Magnetic Particles ◽  
Particle System ◽  
Energy Landscape ◽  
Metastable States ◽  
Field Plane ◽  
The Magnetic Field

The interaction of two magnetic particles separated by an interlayer is illustrated through the "astroid" curves that represent regions in the magnetic field plane where different numbers of minima associated with stable or metastable states may exist. For a single particle, we describe the astroid curves of the Stoner-Wohlfarth model. The case of two particles is then examined and found to be much more complicated. The energy landscape of the two-particle system contains ferromagnetic, antiferromagnetic and canting states that emerge in response to the level of applied magnetic field. Because of this, up to four energy minima can exist in the system, depending upon the strength of the magnetic field and the material properties of the particles.

scholarly journals Experimental Investigation of a Magnetically Balanced Arc in a Transverse Argon Flow

1966 ◽  
Vol 88 (1) ◽  
pp. 27-30 ◽  
Author(s):  
T. W. Myers ◽  
C. N. McKinnon ◽  
J. C. Lysen
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Atmospheric Pressure ◽  
Gas Flow ◽  
Electric Arc ◽  
Test Apparatus ◽  
Gas Velocity ◽  
Argon Gas ◽  
Argon Flow ◽  
Arc Current

An experimental study of an electric arc in crossed convective and magnetic fields has been made. An electric arc was established across a rectangular test section through which argon gas was flowing at approximately atmospheric pressure and velocities up to 100 m/sec. Magnetic field strengths up to 3 webers/m2, oriented so that the Lorentz force opposed the convective force on the arc, were applied perpendicular to both the arc and the direction of the argon gas flow. The test apparatus and the procedure used to obtain the experimental relationship between the velocity of the argon flow and the balancing magnetic field are described. An analysis which assumed the magnetically balanced arc to be a gaseous cylinder positioned between the electrodes and with a diameter varying directly as the arc current satisfactorily explained the observed dependence of the balancing magnetic field on the gas velocity.

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