Optimization And Simulation Of The Radio-freauency Thermal Plasma Reactor

With many advantages,such as high temperature,good thermal conductivity,great cooling rate,controllable atmosphere,etc.,radio-frequency(RF)thermal plasma has been widely used in the preparations of powder materials.In the present work,computational fluid dynamics are applied to simulate the thermal plasma reactor based on Fluent code,and to investigate plasma-assisted preparations of spherical powders and nano-powders by taking melt spheroidization and vaporization as the example.It is hoped to guide the optimization of the plasma reactor and the preparation process.The main results are listed below:(1)Model's foundation,meshing,mesh optimization,calculation boundaries'specification,and characterization of temperature and velocity distributions inside the reactor in three dimensions,are proceed based on the RF thermal plasma reactor in our laboratory.Effect of gas streams' flow rate,involving carrier gas,central gas and sheath gas,on temperature and velocity field inside the reactor is investigated.The regulation laws of the fluid fields inside the reactor are obtained,laying the foundation for studying particles'motion and heat transfer process inside the plasma reactor.(2)For the difficulty of small particles' spheroidization,models are built to simulate the motion of particles with different sizes inside the reactor to investigate the effect of particle size on powders' spheroidization.It is found that small particles are easily affected by axial velocity and radial velocity,obtaining great diffusion and 'back-mixing' phenomena in the reactor,as a result that they cannot absorb sufficient energy,which is the main reason that small particles are difficult to be spheroidized.After the optimization of the flow rate of sheath gas,central gas and sheath gas,particles' diffusion and 'back-mixing' can be reduced,and small particles' spheroidizing effect can be improved.(3)To investigate the effect of particle size on powders' vaporization process,silicon particles' motion and heat transfer process inside the plasma reactor is simulated.By comparing particles' residence time,initial-gasification time and fully-gasified time in statistics,the relationship between gasification ratio and particle size can be obtained.It is found that particles below 30.0?m are 99.0%vaporized in the 30 kW thermal plasma reactor.The impact of particles that are not fully gasified on productions' quality can be neglected.This result is consistent with the actual experimental works,and thus can be applied to guide the selections of raw materials' particle size.(4)To study the effect of particles' feed rate on the vaporization process,silicon powders' heating process in the plasma reactor is simulated.After the calculation of axial velocity and temperature in the reactor,continuous phase's heat flux distribution can be obtained.By its comparison with particles' distribution in radial direction,the effect of particles' feed rate on the gasification ratio can be found out.For the 30 kW plasma reactor,it is shown that particles' gasification ratio is above 99.0%,when the feed rate is lower than 9.63 g·min-1.The impact of particles that are not fully gasified on productions' quality can be neglected.This result can be applied to determine the flow rate of feeding particles.