Research On The Effect Of Structure On Performance In Venturi Powder Injector

Pneumatic conveying technology of dry powder materials has merits,such as flexible layout,no dust pollution,low operation cost and simple maintenance.Thus,pneumatic conveying is widely used in petroleum,chemical,metallurgical,pharmaceutical and mineral processing.Venturi powder ejector is the key device in pneumatic conveying system,studying the characteristics of particles movement and fluid flow and the effect of structure on the transport performance is of great significance.The transportation performance of ejectors based on single-and doubleventuri effect and the influence of nozzle position on the transportation performance of venturi powder ejector were respectively investigated by the experimental method and the numerical simulation based on CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)coupling method.The results show:(1)The wind speed of particle inlet increases due to double-venturi effect,which is beneficial for particles into the injector.The driving force for particles by the fluid increased,which is beneficial for particles to be transferred to a long distance.(2)The closer the nozzle is to the export,the greater injector the wind speed of the particle inlet is and the greater the suction force exerting on particles is.(3)The closer the nozzle is to the export,the less the number of particles deposition in the injector is.The nozzle position y* = 30 mm is the optimal solution to reduce particles deposition.The pneumatic conveying process of venturi powder injector was simulated by using the method of CFD-DEM coupling,and the analysis of the wall stress change due to the impact of particles is carried out by using the method of DEM-FEA(Discrete Element Method-Finite Element Analysis)coupling.The results show:(1)Most of the particles distribute in the middle and lower parts of pipelines in venturi powder ejector,small size particles are faster.(2)The greater the particle size is,the more particle-particle collisionsare and the less particle-wall collisions are.(3)There is peak stress near the nozzle exit and the bottom of the absorbed section.The conveying process of two kinds of non-spherical particles inside venturi powder ejector was respectively simulated by using CFD-DEM coupling approach,and the stress change of walls due to the impact of particles inside ejector was analyzed by using DEM-FEM coupling approach.The results show:(1)Hot spots of particle-wall collision occur around ejector nozzle,there should be reinforcement as needed.(2)Both the number of particle-particle and particle-wall collision of oblate-shaped particles is larger than tablet-shaped particles.(3)The force magnitude of oblate-shaped particles caused by collision is larger than tablet-shaped particles.The effect of structure parameters of venturi tube on the transport performance of the ejector was discussed through CFD numerical simulation of the single gas phase,by the controlling variable method with the same factors and different levels and the orthogonal test with 4 factors 3 levels.The results show that:(1)The larger the throat length is,or the smaller the throat diameter is,or the smaller the contraction angle is,or the smaller the diffusion angle is,the greater the outlet pressure is.The large outlet pressure is benefit for the granular material to be transmitted over a long distance.(2)The influence of the structural parameters on the outlet pressure of venturi injector from large to small are: the throat length,the contraction angle,the throat diameter,the diffusion angle.