Simulation Study And Experiment Of Rice Cleaning Based On DEM-CFD Coupling

Rice is an important food crop in China.Its production,planting area and yield per unit area are all ranked first in the country.Therefore,the mechanization level of rice production is developing rapidly,and the cleaning device is the main equipment for cleaning and removing impurities after rice harvest.The performance is directly related to the impurity rate of the rice after selection.Because the rice cleaning process is a typical gas-solid two-phase flow coupling,it has a certain complexity,it is difficult to describe it by traditional methods,and it is not accurate to interact with the gas and clean objects.The motion change law of the object when it is subjected to airflow.Therefore,based on the discrete element method(DEM)and computational fluid dynamics(CFD)coupling method,the EDEM software and Fluent software coupling method are used to simulate the rice cleaning process.The simulation method simulates the solid phase and the gas phase in different softwares,and transmits the interaction between the solid phase and the gas phase through the coupling interface,which can accurately update the motion behavior of the particles in the flow field and between the flow field and the particles.The interaction is described.This paper summarizes the researches on vibration cleaning,airflow cleaning and other cleaning methods by domestic and foreign scholars.The basic principle of discrete element method and the contact model between particles are described in detail.The computational fluid dynamics method and DEM-CFD coupling are introduced.The related theory,using the “overlapping multisphere clump method” to model the rice,rice straw and broken rice straw particles in the cleaning,and based on the DEM-CFD coupling method,the impurity rate in the rice selection process and The entrainment loss rate is the standard for measuring the effect of cleaning.The simulation process of rice cleaning process is carried out.The separation mechanism of the cleaned objects is described by combining the trajectories and force analysis of different particles in the flow field.The influence of airflow inclination and cleaning method on the cleaning effect,and the water content of the material and the surface energy of the JKR contact model were calibrated.The influence of the moisture content of the material on the cleaning effect was discussed.Finally,the rice cleaning was designed and carried out test.The study found that in a certain range to increase the airflow velocity and the inclination of the airflow,the average impurity rate of the rice decreased,and the entrainment loss rate decreased.Adding a vibrating sieve in the cleaning device can reduce the average impurity rate of the rice,and increase the vibrating sieve.The vibration frequency can further reduce the average impurity rate of rice.After the vibrating screen in the device is inclined by 10°,the average impurity rate of the rice continues to decrease.However,after the vibrating screen is added,the sieve surface collides with some particles to cause the particle to change.There is a trend of movement,so the entrainment loss rate of rice increases after thevibrating screen is added without changing the airflow speed;compared with the dry material cleaning result,the average impurity rate of the wet material after watering increases significantly,and The entrainment loss rate is reduced.The qualitative analysis of the results of rice cleaning experiments under different airflow velocities and airflow dip angles,and the simulation results demonstrate the feasibility of the DEM-CFD coupling method for rice cleaning simulation.The conclusions obtained in this paper provide a useful reference for the design of rice cleaning device,and verify the feasibility of DEM-CFD coupling method for rice cleaning,which provides a new idea and research method for the future simulation of rice cleaning device.