The Coupling Mechanism Of Fluid Dynamics And Heat Transfer Of Siemens Reduction Furnace

Nowadays,solar energy has been obtained more and more attention of the research.As the raw material of solar photovoltaic cells,the demand for polysilicon materials is also increasing.The production methods of polysilicon mainly include improved Siemens process,fluidized bed process,and metallurgical process.In comprehensive consideration,the Siemens method has the advantages of mature technology,high deposition rate,and relatively safe raw materials,and compatible with solar grades and electronics grade polysilicon.It's the mainstream production technology of polycrystalline silicon on the industrial scale.Although the improved Siemens process is relatively mature,high costs and energy consumption are the main problems and obstacles to this method.At present,the research mainly focuses on the radiative heat transfer in the reduction furnace,but it almost not involved in the convective heat transfer in the reduction furnace.The research on the interaction process between flow and heat transfer in the reduction furnace is rarely.In this paper,the flow field and temperature field of the reduction process in Siemens reduction furnace were analyzed,the flow state and the heat transfer process in the reduction furnace were discussed in detail,and the influence of various influencing factors on the convective heat transfer in the reduction furnace was studied.The influence of various factors on the convective heat transfer in the reduction furnace and the interaction mechanism between the fluid dynamics and heat transfer in the reduction furnace were studied.The purpose of reducing energy consumption and reducing production cost is achieved from the aspect of convection heat transfer,Firstly,the convection heat transfer model of the reduction furnace was build based on the laboratory scale Siemens reduction furnace and independent analysis of the model grid was performed.By comparing the calculation results with the experimental data in literature,the accuracy of the model was verified.The influence of different influencing factors on the convection heat transfer in the reduction furnace was discussed,and the convective heat transfer coefficient under the interaction of three factors(Ra,d/L,and X.H)was calculated.The convective heat transfer is significantly increased when Ra is greater than 1.4×10~7,d/L is greater than 0.04,and X.H is greater than 3.0.The contour map of convective heat transfer coefficient in the reduction furnace under different influence factors was obtained and developed the characteristic number equation of convection heat transfer in the reduction furnace.Then,the predicted values obtained by characteristic number equation and calculated by simulation of Nu number were compared when the number of silicon rods is 7 and 8.The average relative errors between the calculated results and the predicted values are 1.4%and 3.2%respectively,indicating the characteristic number equation effectiveness and accuracy.In order to obtain the influence factors and laws of convective heat transfer in an industrial-scale Siemens reactor,a convective heat transfer model for 12 pairs of rod-Siemens reduction furnace in industrial production was established,and the total power of silicon rods in the actual production in the Siemens reduction furnace was compared with the numerical simulation,verified the accuracy of the model calculation results.The influence of factors on the convective heat transfer and convection heat transfer coefficient in the reduction furnace was analyzed.The simulation results show that the flow and heat transfer in the reduction furnace are mixed convection heat transfer with turbulent flow under natural convection and forced convection interaction.Then the influence of different factors on the convective heat transfer in the reduction furnace was studied,and the influence of interactions between different influencing factors on the flow heat transfer coefficient was analyzed.Finally,dimensionless analysis was used to obtain the convection heat transfer correlation in industrial scale Siemens reduction furnace.