Research On Agglomeration Characteristics Of Micro-scale Particles In Turbulent Flow Field

With the rapid development of the national economy,the demand for energy is also growing rapidly.Although China’s consumption of coal is decreasing year by year,it is still the main source of energy.Burning a large amount of coal will produce many suspended particles that are harmful to the human body.In order to solve the problem of particulate pollution,researchers have proposed a series of dust removal methods,in which turbulent agglomeration has the advantages of simple layout and lower cost,which has gradually become a hot spot in the study of fine particle emissions.Based on the research background of turbulent flow agglomeration,this paper numerically simulates the micro-scale particle agglomeration process in the flow field,and analyzes the basic laws of the movement,collision and agglomeration of fine particles in the turbulent flow field from a microscopic point of view.Firstly,the basic theory of turbulent agglomeration is introduced.Through the CFD-DEM coupling mechanism,the interaction between the flow field and the particles,and between the particles and the particles is considered,and the Euler-Lagrangian method is used to simulate the gas-solid two-phase flow problem.This article focuses on the turbulence model,discrete element method,particle contact model,and the coupling mechanism and alternating sequence of computational fluid dynamics and discrete element method.In addition,in order to describe the size and properties of the particle agglomerates,the corresponding particle agglomeration post-processing program was written by using the VB language,and the particle agglomeration efficiency was obtained.Secondly,by constructing the geometric model of the cylindrical turbulence,the LES method is used to calculate the cylindrical turbulence with Re=200,and the complete Karman vortex street phenomenon is simulated,which is consistent with the calculation results in the literature.After the flow field is stabilized,particles of different sizes are introduced at the same time to simulate the phenomenon of turbulent agglomeration.The results show that under the action of turbulence,small particles are distributed in the center of the vortex,while large particles are gathered around the vortex,which greatly improves the particle agglomeration efficiency,and the agglomeration rate in the local area reaches 58.9%.Among them,particles with different particle sizes are easier to adhere,accounting for more than 80% of the total agglomeration number.In addition,the effects of the flow field and the relative turbulent agglomeration of particles are also studied.The results show that with the increase of the gas flow rate,the particle agglomeration efficiency first increases and then decreases,reaching the maximum at 5 m/s.The interaction between particles also plays an important role in turbulent agglomeration.The higher the surface energy of particles,the more conducive to particle agglomeration,but there is also a threshold,and the effect of exceeding the threshold is less obvious.Reducing the coefficient of restitution of particle collisions can effectively increase the momentum loss of the particles and increase the agglomeration rate of the particles.Finally,the turbulent agglomeration simulation of four different shapes of bluff body structures(Cross,triangle,square,ellipse)is carried out under the best working conditions.The flow field generated by different shapes of bluff bodies,the flow characteristics of vortex shedding and the pressure drop of the inlet and outlet fluids are studied,and the bluff bodies with the greatest potential are selected to improve the effect of turbulent agglomeration.The results show that the triangular and cross-shaped structures generate relatively greater disturbances in the flow field,and the pressure difference between the inlet and outlet is also correspondingly increased.The vortex structure produced by them has a relatively larger range of influence,and the vortex structure is broken into many small-scale vortex structures.In terms of particle agglomeration,although the triangular bluff body has the largest disturbance,the cruciform structure has the best agglomeration effect.The use of a cross-shaped bluff body structure can achieve 38.27% agglomeration efficiency of 2μm particles,which is a very large improvement compared to the 9.3% agglomeration rate of the non-turbulent column structure,it plays an important role in the agglomeration and removal of ultrafine particles.