Study On The Effect Of Particle Fluidization Characteristics In Gas-solid Fluidized Bed Under Electric Field

The presence of the electric field in the fluidized bed has an internal electric field and an external electric field.Application of the external electric field can change the state of the force between the particles and affect the formation and evolution of non-uniform structures such as bubbles and clusters in the fluidized bed.The purpose of this work is to achieve the regulation of the fluidized bed flow pattern,so that it is conducive to the actual production in the direction of change.Charge transfer occurs during the frictions and collisions of particle-particle and particle-wall.As a result,these radially distributed charges are excited to form an internal electric field,also called an electrostatic field.Studies have shown that the existence of static electricity on one hand can reduce the size of gas-solid fluidized bed bubble,improve the flow characteristics of particles,strengthen the process of heat transfer and mass transfer,on the other hand may also lead to agglomeration of particles,deteriorate the reaction environment and so on.Therefore,it is of great significance to study the effect of external electric field and electrostatic field in gas-solid fluidized bed.Some of the existing numerical simulations employ a two-fluid model(TFM),which treats the originally dispersed particles as a continuum and establishes the governing equations for the particle phase in the same way as the gas phase.Although the calculation amount is small and it is often used to simulate large-scale equipment such as industrial fluidized bed,it cannot get the detailed motion information of a single particle.Discrete element model(DEM)can track the collision process of particles and obtain the detailed information of each particle from the particle level,which is suitable for the study of particle motion mechanism.Based on the CFD-DEM method,a two-dimensional model of the gas-solid fluidized bed coupled electric field is established and the corresponding numerical simulation is carried out.The influence of a series of characteristic parameters such as the applied DC electric field intensity,the applied AC electric field frequency,the particle charge quantity of mono-charged system and bipolar-charged system on particle fluidization are discussed.The results show that when the intensity of the DC electric field increases,the length of the particle chai ns caused by the interaction between the particles increases,and the number of cluster-like structures caused by the mutual attraction between the particle chains increases,which inhibits the vortex motion of the particles and bubble generation.The change of AC electric field frequency cannot affect the flow characteristics of particles,but only has a weak influence on the force characteristics of particles.Particle fluidi zation characteristics in gas-solid fluidized bed are affected by particle charge distribution.The Coulomb force of the particles increases with the increase of the particle charge quantity,and the Coulomb force of the small particles is higher than the large particles.For the mono-charged system,when the particle charge quantity increases,the number and size of the bubbles gradually decrease until these bubbles disappear,the expansion height of the fluidized bed is obviously increased,and the number of particles in the height direction decreases gradually.The contact force between the particles will increase and the drag force between gas and the particles will decrease.For the bipolar-charged system,when the particle charge quantity is higher,the small particles adhere to the large particles can be formed on the large r size of the cluster structure.The number of the small particles located at the upper part above the large particles increases.The distance that the small particles can reach becomes farther and the contact force of the small particles increase,while the contact force of the large particles decrease,and the drag forces of the small particles and the large particles both increase when the particle has higher charge quantity.