Numerical Study On Flow Characteristics Of Gas-solid Two-phase Flow Field In Typical Pneumatic Conveying And Feeding Device

Pneumatic conveying technology is widely used in many production fields because of its high transport efficiency,small space occupation,low investment cost,and no pollution.As the core part of the pneumatic conveying system,the performance of the feeding device directly determines whether the whole system can run efficiently and steadily.The study of complex gas-solid two-phase turbulent flow in feed device is not enough.Although traditional experimental methods and experiences can be used for design and amplification of devices,detailed two-phase flow characteristics can not be obtained.Numerical simulation technology has an absolute advantage in this respect.In this paper,the most common two feeding devices,the gas-solid injector and the pneumatic conveying tank,were used as the research object of numerical simulation,through the analysis and discussion of the calculation results,provided theoretical basis for its performance optimization.The working principle and design theory of gas-solid injector were analyzed in depth.On this basis,a self-designed gas-solid ejector model was proposed.The two-phase flow field in the ejector was analyzed from three aspects of velocity,pressure and turbulence,and the internal ejection mixing process was discussed in the macro and micro layers respectively.The results showed that the jet flow could be divided into two parts,the core area and the mixing zone,and the secondary flow was ejected in the core region under the action of the mainstream gas which was spewed out at high speed.Under the action of high speed air entrainment,vortices and recirculation on both sides of the core area were observed.The turbulent kinetic energy and turbulent dissipation rate of both phases reached the maximum in the core area.The gas phase and solid phase gradually mixed in the mixing section and diffusion section,and the static pressure gradually increased.As the section area of the turbulent flow beam at the contraction section was larger than the section area of the mixed section,the flow was reflux at the entrance of the mixing section,and the intensity of the turbulence reaches the maximum value here.The asymmetric distribution characteristics of velocity and vorticity in the flow field revealed the flow characteristics of the gas-solid injector.The calculation results of the blow tank showed that there were a lot of whirlpools in the flow field in the tank,and the effect of the gas phase eddy on the solid particles could be divided into two parts.The normal vortex and the spreading vortex could promote the two phases mixing,and the transfer process of the momentum and energy between the phases could be accelerated,the material would be loosened until the transport state was reached.The streamwise vortices mainly played the role of driving material movement.The analysis showed that the gas-solid injector could be optimized by adjusting the vorticity in the injector feeding room,avoiding the large reflux in the injector contraction section and reducing the collision between the two-phase flow and the injector wall.The performance of the blow tank could be optimized by controlling the size of the intake air to adjusting the vorticity of various scales in the flow field.