Numerical Simulation Of Sepiolite Powder Gas-solid Two-phase Flow Based On DPD Method

With the development of ultra-fine powder technology and the in-depth study of sepiolite,sepiolite products with high purity and low particle size have attracted wide attention at home and abroad.Jet classifier is one of the core equipment to realize sepiolite powder purification and classification and the key to its design lies in the study of sepiolite powder gas-solid two-phase flow mechanism.In view of the shortcomings of the traditional numerical methods for gas-solid two-phase flow,the flow behavior of gas-solid two-phase flow in a horizontal pipe is studied in depth based on the dissipative particle dynamics method.This dissertation mainly discusses the following aspects:(1)The theoretical basis of classical dissipative particle dynamics is introduced systematically,including control equation,integral algorithm,parameter selection,calculation flow and so on.Taking air as the research object,the classical DPD method is used to simulate the Poiseuille flow,and compared with the analytical solution to verify the feasibility of the DPD method to simulate the gas phase and the accuracy of the DPD program simulation results.(2)Considering that the soft interaction potential of DPD method is difficult to describe the particle phase,the soft sphere model of discrete element method is introduced,the DPD-DEM coupling model is established,and a more efficient coupling method is proposed.Based on the above model,the classical experiment of Tsuji is reproduced with the same parameters.The comparison with the experimental results shows that the model has high simulation accuracy and good computational efficiency.(3)The physical and mechanical parameters of sepiolite particles needed for simulation are obtained by measurement.Based on these parameters,the flow process of air-sepiolite powder two-phase pipe flow is simulated by DPD-DEM model.The pneumatic conveying characteristics such as flow pattern,horizontal particle velocity,gas velocity,particle concentration and particle distribution are further analyzed,and the formation mechanism of some mesoscopic phenomena in the flow process is revealed.(4)An experimental platform for positive pressure pneumatic conveying of sepiolite particles was set up.The flow characteristics of gas-solid two-phase flow of sepiolite particles in horizontal pipes were measured based on PIV technology,and the results were compared with the simulation results.Within the error range,the experimental results are in good agreement with the simulation results,which verifies the feasibility of DPD-DEM model to simulate gas-solid two-phase flow and the accuracy of predicting the two-phase flow characteristics of air-sepiolite particles.The above research shows that the DPD-DEM coupling model proposed in this dissertation can effectively deal with the problem of gas-solid two-phase flow and realize the study of high gas-solid ratio pipe flow at mesoscopic scale.The flow characteristics of sepiolite powder represented by 5?m particle size are revealed in this dissertation,which provides a mathematical model and theoretical basis for further study on the purification and classification of sepiolite powder under complex flow field.