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.

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.

CORRELATION BETWEEN MICROSTRUCTURE AND YIELD STRESS IN MAGNETICALLY STABILIZED FLUIDIZED BEDS

2010 ◽  
Vol 02 (03n04) ◽  
pp. 185-198
Author(s):  
J. M. VALVERDE ◽  
M. J. ESPIN ◽  
M. A. S. QUINTANILLA ◽  
A. CASTELLANOS
Keyword(s):  
Magnetic Field ◽  
Tensile Strength ◽  
Gas Flow ◽  
Fine Particles ◽  
Contact Forces ◽  
Interparticle Contact ◽  
Gas Velocity ◽  
Jamming Transition ◽  
Interparticle Contacts ◽  
Different Response

A magnetofluidized bed consists of a bed of magnetizable particles subjected to a gas flow in the presence of an externally applied magnetic field. In the absence of magnetic field, there is a given gas velocity at which naturally cohesive fine particles can form a network of permanent interparticle contacts capable of sustaining small stresses. This gas velocity marks the jamming transition of the fluidized bed. For gas velocities above the jamming transition, the bed resembles a liquid. Below the jamming transition, the bed behaves as a weak solid and it has a nonvanishing tensile strength. In the absence of magnetic field, the tensile strength of the solidlike stabilized bed has its only origin in nonmagnetic attractive forces acting between particles. In the presence of a magnetic field, the gas velocity at the jamming transition and the tensile strength of the bed depend on the field strength as a consequence of the magnetostatic attraction induced between the magnetized particles. In this work we present experimental measurements on the jamming transition and tensile strength of magnetofluidized beds of linearly magnetizable fine powders. It is shown that powders with similar magnetic susceptibility but different strength of the nonmagnetic forces show a different response to the magnetic field. This finding can be explained by the influence of the nonmagnetic natural forces on the network of contacts. Thus, our experimental results reported in this paper reinforce the role of short-ranged interparticle contact forces on the behavior of the system, which contrasts with the usual modeling approach in which the magnetofluidized bed is viewed as a continuum medium and a fundamental assumption is that the fields can be averaged over large distances as compared with particle size.

Parametric effects of particle size and gas velocity on cluster characteristics in fast fluidized beds

2000 ◽  
Vol 111 (1-2) ◽  
pp. 114-122 ◽  
Author(s):  
Arun K Sharma ◽  
Kemal Tuzla ◽  
John Matsen ◽  
John C Chen
Keyword(s):  
Particle Size ◽  
Fluidized Beds ◽  
Gas Velocity ◽  
Parametric Effects

scholarly journals PURIFICATION OF SMOKE AND PROCESS GASES IN DIRECT-FLOW CYCLONES

2021 ◽  
Vol 56 ◽  
pp. 44-50
Author(s):  
Valeriy S. Toptalov ◽  
◽  
Nikolai A. Martsulevich ◽  
Oleg M. Flisyuk ◽  
◽  
...  
Keyword(s):  
Particle Size ◽  
Flow Rate ◽  
Gas Flow ◽  
Velocity Profiles ◽  
Geometric Parameters ◽  
Gas Velocity ◽  
Gas Flow Rate ◽  
Direct Flow ◽  
Calculation Results ◽  
Process Gases

In this work, gas velocity profiles in the separating chamber of a direct-flow cyclone are obtained, and a method for calculating its efficiency is proposed. The method allows us to trace the influence of the geometric parameters of the chamber, the particle size and the gas flow rate on the degree of its purification. The calculation results are confirmed by numerous experiments

scholarly journals Segregation patterns in gas-fluidized systems

2001 ◽  
Vol 433 ◽  
pp. 347-356 ◽  
Author(s):  
M. A. GILBERTSON ◽  
I. EAMES
Keyword(s):  
Phase Diagram ◽  
Flow Rate ◽  
Gas Flow ◽  
Fine Particles ◽  
Lower Layer ◽  
Critical Value ◽  
Coarse Particles ◽  
Gas Velocity ◽  
Gas Flow Rate ◽  
Horizontal Band

The formation of segregation patterns in initially homogeneous, fluidized, binary mixtures of particles has been studied. The adjustment of the bed depends on the proportions of fine and coarse particles in the mixture and the gas flow rate relative to the minimum fluidization velocities of the two components. The particles are immobile until the gas flow rate is sufficiently large to fluidize the mixture of particles. When the gas flow rate exceeds this critical value, alternating vertical bands of coarse and fine particles form. At a second critical gas velocity this pattern breaks down and the more familiar pattern of a mixed horizontal band on top of a layer of coarse particles forms. A phase diagram, constructed from experimental observations, shows the conditions for which each of these regimes exists. Its structure is explained in terms of the fluidization and consequent mobility of the mixture components. When horizontal bands are present, the thickness of the lower layer of coarse particles decreases with increasing gas flow rate depending on the proportion of fine particles in the bed. This, and its development, can be understood by analogy with the sedimentation of particles through a turbulent fluid. The experiments imply that the efficiency of mixing by the bubbles in the fluidized bed is very much less than that expected from gas bubbles in a liquid.

INFLUENCE OF PARTICLE SIZE ON THE RHEOLOGICAL PROPERTIES OF MAGNETORHEOLOGICAL SUSPENSIONS

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1416-1422 ◽  
Author(s):  
A.-M. TRENDLER ◽  
H. BÖSE
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Yield Stress ◽  
Fine Particles ◽  
Elastic Behavior ◽  
Shear Load ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Magnetorheological Suspensions ◽  
Field Strengths

Magnetorheological suspensions with different particle sizes including bimodal particle size distributions have been rheologically investigated. The results show a continuous decrease in the base viscosity without magnetic field when increasing the ratio of coarse to fine particles, which is in accordance with the observed trend of sedimentation stability of the samples. However, measurements of the shear stress with a rising magnetic flux density demonstrate higher values for MR suspensions with special mixtures of coarse and fine particles indicating a strengthening of the particle interactions in the magnetic field. The change of the viscoelastic properties of the MR suspensions in dependence on the field strength and shear load (amplitude) have been studied with oscillatory experiments. As expected, at low field strengths, the viscous behavior dominates and, at high field strengths, the elastic behavior, but differences in the crossover field strengths between the two regimes occur for the different particle size distributions. The shear load variation also shows differences between the various MR suspensions indicating the highest yield stress for the sample with only fine particles without magnetic field, but the lowest yield stress at moderate field strengths.

The effect of Tin additionon on Structural and magnetic properties of the stannoferrite Li0.5+0.5XFe2.5-1.5XSnXO4

2016 ◽  
Vol 12 (3) ◽  
pp. 4307-4321 ◽  
Author(s):  
Ahmed Hassan Ibrahim ◽  
Yehia Abbas
Keyword(s):  
Particle Size ◽  
Fine Particles ◽  
Magnetic Moments ◽  
Lithium Ferrite ◽  
Tem Analysis ◽  
Weiss Temperature ◽  
X Ray ◽  
Two Phases ◽  
Nanocrystalline Ferrite ◽  
20 Nm

The physical properties of ferrites are verysensitive to microstructure, which in turn critically dependson the manufacturing process.Nanocrystalline Lithium Stannoferrite system Li0.5+0.5XFe2.5-1.5XSnXO4,X= (0, 0.2, 0.4, 0.6, 0.8 and 1.0) fine particles were successfully prepared by double sintering ceramic technique at pre-sintering temperature of 500oC for 3 h andthepre-sintered material was crushed and sintered finally in air at 1000oC.The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction (XRD) and the Rietveld method.The refinement results showed that the nanocrystalline ferrite has a two phases of ordered and disordered phases for polymorphous lithium Stannoferrite.The particle size of as obtained samples were found to be ~20 nm through TEM that increases up to ~ 85 nmand isdependent on the annealing temperature. TEM micrograph reveals that the grains of sample are spherical in shape. (TEM) analysis confirmed the X-ray results.The particle size of stannic substituted lithium ferrite fine particle obtained from the XRD using Scherrer equation.Magneticmeasurements obtained from lake shore’s vibrating sample magnetometer (VSM), saturation magnetization ofordered LiFe5O8 was found to be (57.829 emu/g) which was lower than disordered LiFe5O8(62.848 emu/g).Theinterplay between superexchange interactions of Fe3+ ions at A and B sublattices gives rise to ferrimagnetic ordering of magnetic moments,with a high Curie-Weiss temperature (TCW ~ 900 K).

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