Study On The Motion Characteristics And Heat Transfer Characteristics Of Ellipsoidal Particles In The Vertical Heat Exchange Tube

Liquid-solid two-phase flow heat exchanger is widely used in chemical industry,seawater desalination and other industrial fields.Solid particles have efficient heat transfer performance by enhancing fluid disturbance in tube.Therefore,it is of great significance to further improve the working efficiency of liquid-solid two-phase heat transfer equipment to explore the interaction process of liquid-solid two-phase flow.In this paper,the development status and existing problems of liquid-solid two-phase flow technology are introduced.Numerical simulation of liquid-solid two-phase flow in vertical heat exchange tube in liquid-solid two-phase flow heat exchange equipment is carried out,and corresponding conclusions are obtained,which has certain guiding significance for the design of liquid-solid two-phase flow heat exchanger.The paper mainly includes the following contents:?1?The reliability of the CFD-DEM coupling method is verified by comparing with the particle velocity in literature experiments.Based on it,75 different working conditions were constructed for the subsequent research on the influence of the aspect ratio?,particle inlet volume concentration?_inand fluid inlet velocity v on the motion and heat transfer characteristics of the ellipsoid particles in the tube.?2?The influencing factors of the distribution characteristics of ellipsoid particles?particle distribution position,mass flow rate,particle orientation angle?in the vertical heat exchange tube were studied.The simulation results show that the interaction between liquid and solid can significantly affect the distribution of particles in the tube.The larger the particle inlet volume concentration,the smaller the change of particle mass flow in the monitoring segment,and the more stable the particle movement in the tube.The ellipsoid particles with the length-diameter ratio?=1.5 have the most violent movement in the tube,the maximum peak value of the probability curve of the included Angle of particle orientation,the maximum area of the interaction between particles and fluids,and the maximum interaction force.?3?The motion characteristics of five kinds of particles in the vertical heat exchange tube with the length-diameter ratio?=1.0,1.5,2.0,2.5 and 3.0 were numerically simulated.The results show that the axial and radial forces of the?>1.0ellipsoid particles fluctuate more than those of the?=1.0 spherical particles.During the bottom-up movement,the average velocity of the particles in the tube firstly increased and then decreased,and finally tended to be stable dynamically.The average velocity of the ellipsoid particles with the length-diameter ratio?=1.5fluctuated the most.In the central region of the tube,the?=1.5 ellipsoid particles had the worst"following feature",while the?=1.0 spherical particles had the best"following feature".At the same time,the concentration of the five kinds of particles tends to increase in the near-wall area.With the increase of fluid inlet velocity,the concentration of the particles decreases in the near-wall area.With the increase of the inlet volume concentration of particles,the concentration of particles in the near-wall area first increased and then stabilized.?4?The effects of the ellipsoidal particle's aspect ratio?,particle's inlet volume concentration?_inand fluid inlet velocity v on the heat transfer characteristics of the ellipsoidal particle in the tube were studied.The simulation results show that the five kinds of particles can significantly enhance the radial velocity fluctuation of the fluid and cause the radial migration of the core area of the velocity field in the tube.The five kinds of particles can also significantly increase the turbulent kinetic energy of the flow field.The enhanced heat transfer capacity of the particles was evaluated based on PEC index.Within the parameter range of 1.5???2.5,2%??_in?4%,1.0m/s?v?1.5m/s,the PEC index of ellipsoid particles is greater than that of spherical particles,indicating that ellipsoid particles have a stronger heat transfer advantage than spherical particles.