The Research On Characteristics Of Particles Flowing Around The Tube

Particle flow refers to motion state which is similar to fluid when particles is under exogenous action or internal stress changes.It widely exists in agriculture,chemical industry,metallurgy,energy resources,pharmacy,etc.The process that gravity flowing bed exhaust-heat boiler retrieves residual heat of high-temperature slag is virtually heat-transfer process that high-temperature particles flow over heat exchanger.The flowing characteristics of particles affect heat recovery efficiency.Nevertheless,the flow mechanism of particles remains to be solved.So,it not only has important scientific sense,but also makes a great contribution to energy-saving and emission-reduction of iron and steel industry.It makes sense to optimization of equipment structure and improvement of heat-transfer efficiency that understanding flowing characteristics of particles.This article establishes experiment platform of gravity flow bed exhaust-heat boiler.This experiment uses glass balls to study flow characteristics of particles on the condition of invariant height of particles and analyze the influence of tube diameter,particle diameter,tubes arrangement way,tubes row number,the distance between center of tube and wall and size of outlet on flow-rate,particle trajectory and flow pattern.The process of particles discharged continuously was simulated by commercial software EDEM which analyzes the influence of tube diameter,tubes arrangement way and tubes row number on flow pattern,particle trajectory,velocity and stress distribution.The main research content and results are as followings:(1)At the beginning of discharged time,the flow-rate increases and fluctuates as time goes by.The flow-rate is mainly influenced by diameter of particle and size of out.It increases as the particle diameter decreases and size of outlet increases.Particle diameter,the tubes arrangement way,tube row number and distance between tube center and wall have a little influence on flow-rate.The bigger flow-rate is,the bigger fluctuation is.(2)The particle trajectory is mainly influenced by diameter,the tube arrangement way and distance between center of tube and wall.The bigger diameter of tube is,the bigger trajectory changed when particles flow over tube.Tubes staggered arrangement can change the particle trajectory from upright to S type.The trajectory of particles over tube deviates to center of tube as interval between center of tube and wall.(3)The particle diameter has a great influence on flow pattern.The bigger particle diameter is,the smaller staggered arrangement is,the worse of force uniformity is,the better mixing is.The bigger diameter of tube,the bigger dead zone among tubes is.Tubes staggered arrangement can reduce the region of dead zone among tubes.The more row number of tubes,the denser force nest among tubes is,the more obvious inhibition is,the bigger region of dead zone among tubes is.The closer distance between tube center and walls is,the worse particle flow integrally is,the bigger region closed to wall is.The bigger size of outlet is,the better mixture efficiency of particles per meter while dropping down,the easier tracer particles mix with others.(4)The Hertz-Mindlin contact model can predict particle flow characteristics.As diameter of tube becomes larger,region among tubes becomes larger,it becomes more difficult for particles to get out of dead zone,so it moves around tubes.When passageway faces to outlet,the resistance of particles is least,fluctuation of trace is least,velocity is fastest.The force distribution of different tubes are similar,force is biggest over tubes and funnel part.The bigger diameter of tubes is,the bigger area of cavity under last row of tubes.(5)When tubes staggered arrangement,the tubes affect the particles strongly,particles horizontal displacement increase and particle becomes S-shaped,the area of dead zone among tubes becomes smaller,velocity of particles beside tubes is in an unequal distribution.When tubes staggered arrangement,the force on the funnel part is bigger.(6)The less row number of tubes,the better tracer particle flowing characteristics are.Velocity of particles distributes unequally beside tubes,but equally without tubes.Tubes have an influence on particles,the more row number of tubes is favorable to mixture of particles,at the same time,the smaller force of the wall is.