Study On Particle Flow Characteristics In Magnetic Field Fluidized Bed Under Microgravity

Magnetic fluidized bed,which is a kind of fluidized bed reactors with an external energy field,has attracted more and more attention from researchers due to its advantages including low vibration and noise,easy loading and unloading and high heat and mass transfer rate.In order to analyze the particle flow characteristics in magnetic fluidized beds and guide industrial production and reactor design,a great deal of researches on magnetic fluidized beds have been conducted.However,it still has some limitations in the field of microgravity.In addition,most of the current researches mainly focus on the analysis of particle flow characteristics in a single component particle system in a magnetic fluidized bed,but in actual production and life,it is inevitable that a variety of component particles will appear.Therefore,this thesis takes binary particle systems(magnetic and non-magnetic)as the research object,and analyzes the flow characteristics of binary particle in a magnetic field fluidized bed under the condition of microgravity and the gas-solid two-phase flow behavior in the particle system by means of numerical simulation.Based on the soft sphere model of discrete element,the soft sphere model of discrete element of magnetic particle was established by adding the magnetic field force model to the external force term of particle and considering the effect of external magnetic field force on particle flow characteristics.Navier-Stokes equation is used to numerically solve partial differential equations for gas phase and magnetic force is considered in solid force.Gidaspow drag force model is appled for the momentum exchange between gas-solid phases.Model verification is done to validate the mathematic model.Using the soft sphere model with the magnetic field force,the fluidization behavior of binary particles in a fluidized bed with magnetic field under gravity is numerically simulated.It is found that proper magnetic field intensity,magnetic field gradient and apparent gas velocity can improve the particle separation under the conditions of this work.Using the soft sphere model with the magnetic field force,the fluidization behavior of single component particles in a magnetic fluidized bed and without magnetic field under microgravity was numerically simulated.Results show that the bubble growth can be effectively inhibited and the particle fluidization can be more uniform adding suitable gradient magnetic field.There is almost no particle formation into chains or clusters by the combined action of the magnetic field force between particles and the gradient force of the outer magnetic field.Moreover,due to increasing the force of particles along the direction of gravity,that is,increasing the "gravity" of particles,the range of particle fluidization operable gas velocity becomes wider.Using the soft sphere model with the magnetic field force,the fluidization behavior of particles in a magnetic fluidized bed with binary particle under microgravity was numerically simulated.It is found that in microgravity environment,adding a suitable gradient magnetic field can promote the mixing degree of two kinds of binary particle with a density difference of 28%,but too high magnetic field intensity will cause the magnetic particles to form clusters.