Simulation Analysis And Research On The Screening Process And Airflow Field Of Rotary Combined Multi-layer Screen

Screening and air selection are important links in grain removal.The rotary combined multi-layer screen is a large-volume,high-efficiency grain cleaning equipment that combines air selection and screening.The rotary combined multi-layer sieve is a grain cleaning screen which is improved on the basis of the original plane rotary screen and has four sets of eight-layer sieve surfaces.During the screening process of materials,the grain particles collide with the foreign particles,and the movement is more complicated.There is also a close relationship between the movement parameters of the sieve body and the screening yield and screening efficiency.The structure of the channel system is complex,and the flow of the internal airflow field cannot be accurately observed.In this paper,the multi-layer sieve of rotary combination is taken as the prototype to study its screening system and wind selection system.The three-dimensional modeling software Solidworks is used to establish the three-dimensional solid model of the rotary combined multi-layer sieve.The movement of the four sets of sieves in the rotary combined multi-layer sieve is the same,so one of the sieve faces is taken as the research object,and the screening process is studied.Because the upper surface of the rotary combined multi-layer sieve mainly cleans the large impurities,the lower sieve surface mainly cleans the small impurities,and the main cleaning objects of the two-layer sieve surface are different.Therefore,the discrete element simulation software EDEM is used to separate the upper sieve in the screening process.Numerical simulations of the material flow motion of the face and the lower screen.The fluid dynamics simulation system software Fluent was used to simulate the airflow field of the air duct system in the rotary combined multi-layer screen air separation system.The main work of the thesis is as follows:(1)The research on the rotary combined multi-layer screening system is carried out,mainly to study the relationship between the movement of material particles on the upper and lower screen surfaces and the movement parameters of the screen surface and the material advancing speed and screening efficiency.A wheat grain model,a stalk model,and a rock model were established in EDEM.The contact properties between different materials,the movement parameters of the sieve and the particle factory were set up.The three-dimensional model of the superimposed multi-layer sieve was introduced into the discrete element simulation software EDEM for numerical simulation.The control variable method was used to change the movement parameters of the screen surface such as the radius of slewing radius,the inclination angle of the screen surface,and the rotation frequency of the screen surface,and the movement of the material flow under different motion parameters and the morphology of the sifting of wheat and stem were obtained.The relationship between different motion parameters and material advancement speed,impurity removal rate and grain extraction rate can also be obtained to obtain the optimal screening motion parameters.(2)The four-factor three-level orthogonal experiment was used to simulate the screening process of the rotary combined multi-layer sieve.On the basis of the three factors of the radius of slewing of the screen surface,the inclination angle of the screen surface and the frequency of the screen surface rotation,the factor of material impurity content is introduced.The propulsion speed and screening efficiency of the materials in the nine orthogonal simulation experiments were separately calculated,and the difference method was used to analyze the influence of these four factors on the propulsion speed and the screening efficiency,due to the two indexes of propulsion speed and screening efficiency.The optimal motion parameter combination determined by the value is different.Therefore,the matrix matrix method is used to obtain the weight matrix of the advancing speed and the screening efficiency respectively.The total weight matrix obtained by adding the weight matrix of the two indicators is used to obtain the material advancing speed.Combined with the optimal motion parameters of the screening surface for screening efficiency.(3)Carry out the study of the airflow dynamics in the rotary combined multi-layer screen air-selection system.Since the entire wind-selection process takes place in the air duct system,the fluid dynamics simulation software Fluent is used to convert the airflow in the combined multi-layer screen duct system.The field is simulated,and the eddy current area,the high airflow velocity,and the small-speed settlement area are small according to the airflow field in the sedimentation chamber of the air duct system.By changing the position and structure of the upper and lower sedimentation chamber windshields,the wind speed in the airflow field of the sedimentation chamber is adjusted,the airflow instability in the settlement chamber is reduced,the eddy current generation is reduced,the impurity sedimentation effect is improved,and the air separation efficiency is improved.The velocity cloud map,vector diagram and wind speed curve of the monitoring point under the structure verify the influence of structural changes on the airflow distribution and wind speed variation in the settlement.