Study On Motion And Structure Characteristics Of Dense Granular Impinging Jet

Impinging jet is widely used in industry because of its good heat and mass transfer and mixing characteristics,which has important theoretical research value.At present,the research of impinging jet mainly focuses on single-phase and sparse gas-solid two-phase impinging jet,while the study of dense two-phase flow mainly focuses on dense granular jet and dense granular wall impinging jet.The research of dense granular opposed impinging jet,which is more common in industrial practice,is almost blank.Based on this,in this paper,the discrete element simulation software EDEM 2018 and the data post-processing program based on MATLAB platform are used to simulate the macro motion characteristics of particles and the multi-scale structure characteristics of the granular film in dense granular impinging jet under different solid fraction,particle diameter,nozzle diameter,particle velocity and nozzle spacing.Through the application of self-developed data post-processing program,firstly,the distribution laws of motion characteristics statistics such as particle concentration,collision,velocity,particle temperature and pressure in dense granular impinging jet are obtained;then,the evolution rules of impinging plane motion pattern are explored,and the granular film structure characteristics are obtained by using Galileo decomposition idea and modeling method,including the number of wave layers and the enrichment width of the particle group,the wave structure gap and the average concentration of the particle enrichment area;finally,the formation mechanism of the wavy structure on the impinging plane is revealed.The research results show that the dense granular impinging jet forms a disc-shaped stagnation plane in the impinging zone.As the particle solid fraction and the ratio of the nozzle diameter to the particle diameter increase,the axial particles cannot penetrate the stagnation plane and gather on both sides of the stagnation area,and the particle concentration on the axis evolves from single peak to bimodal distribution.The particle collisions are mainly concentrated in the collision area;with the increase of the particle solid fraction and the ratio of the nozzle diameter to the particle diameter,the particle collision frequency increases linearly,while the collision force is greatly reduced,and the particle pressure increases;the higher the collision frequency between particles,the lower temperature of the particles.In addition,with the increase of the particle solid fraction and the ratio of the nozzle diameter to the particle diameter,the violent interaction of the impinging zone promotes the impinging plane to evolve from diffuse pattern to the granular film;and the larger the ratio of the nozzle diameter to the particle diameter,the lower the critical particle solid fraction,that is,the easier it is to form granular film on the impinging plane.The granular film structure of the impinging plane can be divided into disk stagnation zone,transition zone and fully developed wave zone.The diameter of the disk stagnation zone increases linearly with the increase of the particle solid fraction and the ratio of the nozzle diameter to the particle diameter;the enrichment width of the particle group and the gap width in the fully developed wave zone decrease with the increase of the ratio of the nozzle diameter to the particle diameter,and the number of wave layers gradually increases.The average concentration of the particle enrichment area increases with the increase of the particle solid fraction and the ratio of the nozzle diameter to the particle diameter,and shows a trend of first decreasing and then increasing with the increase of the particle diameter.The area near the stagnation point where the particle velocity is low and the velocity change rate is low is characterized as "dead zone" structure.The particles in the stagnant zone interact with the particles in the "dead zone" structure to exchange momentum,and the speed decreases,while the speed of the particles in the outer zone remains unchanged.There is speed difference between the inner and outer layers of the granular film,which appears as wave structure on the impinging plane.