Research On Synergistic Action Of Large Particle Fluidization Characteristics And Heat Transfer

This paper selects the glass beads to replace of silicon particle in polysilicon production as the experimental material,which size range of 0.1 mm to 0.5 mm.Frequency response technique is used to study the heat transfer between particles and fluid characteristics,and the influence of Grain size,fluidizing gas velocity and bed void fraction was investigated.17 groups of coefficient of heat transfer between particles and fluid flow characteristics in fluidized bed and fluid property was determinate in the experiments.Heat transfer correlation was got by using regression analysis.Then the heat transfer correlations were used in the Fluent,and simulate the process of gas-solid unsteady heat transfer,the simulation results are compared with Guun heat transfer model and the experimental results.The influence to the fluidization and heat transfer characteristics were also studied when fluidized bed was built-in vertical convection heating rod.Specific content is as follows:1.Gas-solid fluidized bed experimental device with 0.16 m diameter and 1.3 m high was set up to study the fluidization and gas-solid heat transfer characteristics.Temperature control system can output sinusoidal temperature change with amplitude in the 5-10?,cycle in more than 90 s.Using the K type thermocouple to acquired gas temperature with five times per second.Set1-Set3 are narrow screening particles,Set4 and Set5 are wide screening particles,Sampling method is used to measure local particle volume fraction,differential pressure gauge is used to determine pressure change.2.Particle size and fluidizing gas velocity is the mean factors to the heat transfer coefficient between particles and fluid,but not the change of the temperature parameters at the entrance.The heat transfer coefficient will be higher with larger particle size and greater gas velocity.In this paper,the heat transfer coefficient between particle and fluid is 10 times bigger than the empirical value,and get heattransfer correlations from 17 groups of experimental data:0.648 1/2 0.33Nu3.37 Re ?Pr-(28)?(1<Rep<11).The error between calculated value of correlations and experimental value is within 15%,meeting the demands of engineering calculation accuracy.3.The radial and axial particle volume fraction distribution,the height of the bed in the simulation of the gas-solid unsteady heat transfer,was consistent with the experimental results.The analysis of particles' instantaneous velocity vector shows that there are particles circulating movement from the center to the sides as a whole and local vortex in fluidized bed.Heat transfer between particles and fluid is mainly in fluidized bed entrance to a small area.The simulation of particle heating curves with the User-defined heat transfer model are same to the experimental results,but Guun heat transfer model is lower than the experimental results.The instantaneous temperature of particles is associated with the speed of the gas at the fluidized bed entrance,which is proportional to the particle Reynolds number.4.Bubbles are produced mainly along the wall.Internals in fluidized bed break bubble,and increase the content of solid bed the center,which lead to the bed particle size distribution more uniform.By contrasting gas pressure changes in the fixed position before and after adding inner component found that,the bubbles crushing frequency was not significantly changed,but the size of the bubble decreases.It does not change the temperature of the fluidized bed of gas and particles in the overall distribution after adding internals,but the built-in heating rods heating form,can significantly reduce the fluidized bed wall temperature,which can effectively reduce the surface sediments in the polysilicon production.