CFD Simulation Of Chemical Vapor Deposition(CVD) In Solar Grade Polysilicon Fluidized Bed Reactors

Increases in solar energy utilization have resulted in a strong demand of solar grade polysilicon(SGP).However,the high energy consumption and the difficulty in exhaust treatment of polysilicon technologies,which is existing call for alternative technologies.In recent years,silane fluidized bed CVD reactors are actively developed for a high utilization rate of materials and a lower energy consumption rate.Due to the complexity of two-phase flow in fluidized beds and the cluster forming from homogeneous decomposition of silane,the scale-up of the CVD-FBR faces difficulty.Compared with experiments,numerical simulation has advantages for analyzing the flow characteristics of silane fluidized bed and deposition process,hence it is applied in the present study.To find a suitable drag model in coarse grid condition,the classic Gidaspow model and a sub grid model(SGS Model)drag force model were validated against literature reported experimental data for a square fluidized bed of Geldart B particles.The results confirmed the feasibility of the SGS model for coarse grid computations.A cylindrical silicon-CVD fluidized bed was simulated with the SGS model,and the simulated bed expansion height and the average bubble size were compared with the empirical formulas.The deviation of bubble size from SGS model is 12.6%comparing with Mori-Wen's empirical formula,which is smaller than the deviation of 21.4%obtained from Gidaspow model simulation.The chemical vapor deposition kinetics of Hogness and a surface deposition kinetic model of Iya were chosen to simulate a polysilicon fluidized bed of I.D.0.1524 m with population balance model(PBM Model).Comparing with Hsu's experiments,the deviation of predicted Si-growth rates is 6.4%for 20%SiH4 inlet concentration,and 5.6%for 50%SiH4 inlet concentration.Deposition rate of I.D.0.5m fluidized bed under different characteristics of flow was also discussed,and the results are reasonable.