Study On Drying Process Of Silicon Particles Based On CFD-DEM

As the shortage of traditional energy is increasing,the photovoltaic industry has been developing rapidly and solar photovoltaic power generation technology is widely popular in people’s lives.Silicon wafers for photovoltaic power generation need to consume a large amount of silicon particles in the production process,requiring silicon particles need to have a good quality.Silicon material drying is the last step in the production process of automatic ultrasonic cleaning machine,and is also one of the most important links,the study of the drying process of silicon particles in the workwear basket of this link is of great significance for the energy saving of the drying device and the optimization of the structure of the workwear basket.In this thesis,the airflow field at the nozzle of the gas flow channel of the workwear basket is simulated by CFD numerical simulation,and a more uniform distribution of the nozzle is determined according to the velocity and flow rate of the airflow;the movement and mixing of the silica particles in the workwear basket is simulated by DEM numerical simulation,and the movement mode,optimal process and optimal structural parameters of the workwear basket are determined according to the movement trajectory,Lacey mixing index and mixing rate of the particles.parameters and optimal structural parameters;the heat transfer process of the silicon material inside the workwear basket was simulated by coupled CFD-DEM numerical simulation,and the most energy-efficient process parameters for drying were determined based on the temperature distribution and the average temperature of the silicon material;the concrete discuss and plan work is as follows.First of all,the drying process of silica pellets was investigated and it was found that there were problems such as uneven axial drying,uneven mixing and uneven radial drying during the drying process.In order to solve the corresponding problems,studies on airflow field characteristics,silicon particle mixing characteristics and heat transfer characteristics were carried out respectively.Then,a 3D CFD model of the workpiece basket was constructed,based on which the airflow field at the gas flow channel nozzle was simulated,and the effects of several process parameters and structural parameters on the properties of the airflow field at the nozzle were studied.A new design of the air flow channel and segmented nozzle distribution design are proposed to reduce the pressure difference generated below the nozzle of the gas flow channel,so as to reduce the generation of negative pressure and make the air emitted from the nozzle have good uniformity in velocity and flow rate.The results show that a suitable reducer cone,inlet width and velocity,as well as an appropriate pitch distribution can effectively improve the airflow uniformity and thus the drying performance of the whole unit.Next,according to the above results,a three-dimensional geometric model of the new workwear basket is established.Based on this model,the motion mixing of silicon particles in the workwear basket is simulated by DEM.The final simulation length was determined by length-independent verification and the movement was determined by analysis of the two types of movement of the workwear basket.The effects of process parameters such as workwear basket speed,particle filling rate,stirrer structure and number on the mixing of silicon motion were investigated.Studies have shown that fill rate has a small effect on particle mixing and that choosing the ideal fill rate,speed and shape and number of stirrers can improve the mixing effect and mixing rate.Finally,a three-dimensional geometric model is recreated based on the above results,on the basis of which the heat transfer process of the silicon particles in the workwear basket is simulated.The effect of process parameters such as the speed of the workwear basket,the particle filling rate and the number of radial nozzles on the heat transfer of the silicon material is investigated by a coupled CFD-DEM numerical simulation method.The optimization scheme was designed using the orthogonal test method,and the significance among the factors was obtained by the methods of extreme difference analysis and analysis of variance.The optimal combination was obtained by using the single-factor multiple comparison method,and the optimal combination of process parameters was verified by simulation to finally determine the best energy-saving process parameters for the workwear basket.