Study On The Gas Flow Field In The Reaction Chamber For Preparing Alumina Nanometer Powders

Alumina has good chemical stability,abrasion resistance and adsorption.And alumina nanometer powders is suitable for heat insulation materials.At present,the main methods for preparing alumina nanometer powders are solid phase method,liquid phase method and chemical vapor deposition method.Among them,Chemical Vapor Deposition(CVD)is expected to be a large-scale preparation method for high quality alumina nanometer powders.It makes aluminum chloride and water vapor react in the reaction chamber to form alumina nanometer powders.In recent years,preparation of alumina nanometer powders has been studying at home and abroad.But few researches on the effects of the gas flow field in the CVD reaction chamber on the preparation of alumina nanometer powders are reported.However,the gas flow field in the reaction chamber is an important factor in preparing alumina nanometer powders.Higher quality alumina nanometer powders can be prepared by changing the reaction chamber parameters to change the gas flow field.However,it is difficult to study the gas flow field in the reaction chamber with experimental methods because of the high cost and long period.The numerical simulation method can reveal the characteristics of the gas flow field conveniently and quickly.In this thesis,the gas flow field in reaction chamber is studied by numerical simulations.This thesis mainly includes three parts.In the first part,the gas flow field model in the chemical vapor deposition reaction chamber is established.The preprocessing software GAMBIT is utilized to build the geometry model and generate mesh of the reaction chamber which are imported into the Computational Fluid Dynamics software FLUENT.The pressure solver and standard k-? turbulence model are chosen.The energy equation is activated.Reaction conditions are set.The component transport equation is established.The boundary conditions are defined.The velocity,temperature and composition proportion are initialized.In the second part,the gas flow field in the reaction chamber is simulated numerically.The model control equation is iteratively solved.Distributions of the gas velocity,temperature,reactants concentration and alumina concentration are obtained.Several cross sections are taken in the reaction chamber.The concentration distributions of reactants and products are investigated and compared along these cross sections.The reaction conditions are analyzed in the reaction chamber.In the third part,effects of relative parameters of the reaction chamber on the gas flow field are studied.The velocity distribution,temperature distribution and concentration distribution of the gas flow field are compared by changing the inner ring diameter,the reaction chamber diameter and the aluminum chloride inlet velocity.It is found that the larger the inner ring diameter,the higher the gas velocity;The reaction chamber diameter has little effect on alumina concentration,but increasing reaction chamber diameter can increase the reaction efficiency.The higher the inlet velocity of aluminum chloride,the higher the concentration of alumina nano powder.In this thesis,the gas flow field in the reaction chamber for preparing alumina nanometer powders is modeled and simulated.The environmental characteristics for forming alumina nanometer powders are revealed,which lays a foundation for further researches on the CVD forming mechanism of alumina nanometer powders.