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

Abstract

This 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 µm 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.

Effect of particle size polydispersity on the yield stress of magnetofluidized beds as depending on the magnetic field orientation

“…In the co-flow configuration, the gas flow promotes the formation of chainlike aggregates vertically oriented and parallel to the external magnetic field along which the attractive forces reach their maximum value. Thus, stronger interparticle interactions are induced in this case for a given intensity of the magnetic field, which precludes the development of bubbles at higher gas velocities [84,85].…”

“…Thus, the average angle between the strings of chained particles and the magnetic field direction depends also on particle size. Presumably due to this effect, in the cross-flow configuration, the magnetic yield stress is seen to increase with particle size whereas the opposite trend is found when co-flow magnetic fields are applied [84,85].…”

“…At the same time, the first practical applications based on MFBs were being envisaged [74][75][76][77][78]. During the next two decades, the improvement of experimental devices and techniques for the synthesis of magnetizable particles cleared the way to further research on the effect of the imposed magnetic field orientation [79,80] or the use magnetizable particles with tailored properties [81][82][83][84][85] as well as gas-liquid-solid admixtures [86][87][88]. New industrial applications have emerged in bioreactors [89,90] and aerosol filtration [91].…”

Optimisation of Automatic Dosed Mould Filling With Ferromagnetic Powders

“…По мере уменьшения размера частиц возрастает их взаимодействие, что приводит к изменению технологических характеристик дисперсной среды [1]. Накоплен значительный теоретический и экспериментальный материал о влиянии магнитных полей на реологическое состояние магнитных жидкостей [2][3][4], дисперсных материалов, находящихся в псевдоожиженном состоянии [5][6][7], порошков магнитных материалов при сепарации, измельчении и прессовании [8][9][10]. Специфика поведения порошков на различных этапах обработки и целесообразность технологического процесса, обеспечивающего выпуск продукции с заданными конечными свойствами, во многом определяются физико-технологическими свойствами порошков [11][12][13][14][15].…”

Technological processes intensification in devices with magneto-fluidized bed

“…Particle size decrease increases interparticle interaction leading to changing of particulate system technological characteristics [1]. Considerable theoretical and experimental material about influence of magnetic fields on rheological state of magnetic fluids [2][3][4] and particulate materials in fluidized state [5][6][7] was accumulated. There is a wide range of devices that fluidize particulate medium by means of hydration, aeration, ultrasonic, electrodynamic and electromagnetic effects [8][9][10][11].…”