Experimental And Simulation Study On Flow Field Characteristics Of Upward Liquid-solid Two-phase Flow In Convergent-divergent Tube

The converging-diverging tube liquid-solid two-phase flow heat exchanger had the advantages of compact structure,low equipment renovation cost and high heat exchange efficiency,and can be widely used in chemical,energy and metallurgical industries.However,the flow characteristics inside the liquid-solid two-phase flow in the converging-diverging tube were complex,and the heat transfer law between the fluid and the tube wall was complicated and difficult due to various factors,which made the engineering design of the liquid-solid two-phase flow in converging-diverging tube complicated and difficult.Therefore,it was of great significance to study the liquid-solid two-phase liquid flow behavior and particle motion trajectory in the tube to reveal the effect of flow field on heat transfer.In this study,the particle image velocimetry(PIV)technique was used to obtain the distribution law of the vorticity field,velocity field and turbulent kinetic energy in the tube.On this basis,visualization technology and CFD-DEM dynamic simulation technology were used to obtain particle trajectory and particle force,and to explain the characteristics of flow field changes.The main contents of the paper are as follows:1、In this study,PIV was used to explore the behavior characteristics of the upward liquid-solid two-phase flow in the converging-diverging tube,and the vorticity value and turbulent kinetic energy were compared with the light tube,the liquid-solid two-phase flow,and the converging-diverging tube.The influence of u,ψ,Φ on the liquid-solid two-phase flow field in the pipe was studied by orthogonal analysis method,and the distribution of fluid vorticity,radial velocity and turbulent kinetic energy in the tube was obtained.The results show that the strength of the three factors was Φ<ψ<u.The average vorticity of the whole,the average vorticity of the near-wall region and the peak radial velocity are positively correlated with the u and ψ,but negatively correlated with Φ.In the experimental range,the average turbulent kinetic energy of u=1.0 m/s was increased by 123.91% compared with 0.6 m/s,the average turbulent kinetic energy of particle volume concentration 5% was increased by 31.77% compared with 1%,and the average turbulent kinetic energy of particle size 1.5mm was increased by 4.08% compared with 5mm.2、By independently building a particle visualization experimental platform,two high-speed cameras was used to take pictures of the upward particle movement in the tube,and the three-dimensional movement trajectory of the particle was obtained through image recognition,module processing and probability statistics.The results show that: after adding particles into the converging-diverging tube and the light tube,the collision frequency of the particles in the converging-diverging tube and the wall was higher,and the motion trajectory became a periodic and regular upward movement.And with the increase of u and ψ,the fluidization of particles was enhanced,but with the decrease of Φ,the effect of particles following the fluid was better.3、In order to obtain the dynamic characteristics of the particles in the tube,the numerical simulation method CFD-DEM was used to analyze the particle velocity,particle angular velocity,and the resultant force of the particles on the X,Y,and Z axes under different u,ψ,and Φ.The particle velocity,the particle angular velocity and the average resultant force on the particles in the X,Y and Z directions were positively correlated with u and ψ,but negatively correlated with Φ.