Numerical Simulation And Experiment Of Gas-solid Two-phase Flow In A Novel Grain Separation Unit

In this dissertation, the domestic and foreign research condition of the separation unit is introduced. A cross-flow air separation unit is put forward according to some existing problems on the design and research of the separation unit. Finally the prototype was designed and manufactured. The novel separation unit has three main characteristics. Firstly a horn-shape channel was designed which can ensure the inlet of the separation chamber consistent with the air outlet. Therefore the airflow can uniformly distribute in a direction perpendicular to the flow velocity and enhance the air velocity when the air enters the separation chamber. Secondly two cross-flow fans were used as the wind source which can generate the uniformly distributed airflow along the fan axis. Last two oppositely rotating feeding rollers were employed which grind the crop material into thin layer when the crop material enters the cleaning chamber. Thus most straw pieces could turn their longitudinal axis perpendicular to the wind direction so that the straw pieces could be separated from the grain as soon as possible.For pure air movement, the movement and distribution of air in the channel and cleaning chamber were studied based on the gas phase k-s turbulent model. The discrete element method (DEM) was introduced to establish the mechanics model of the discrete solid particle. The equation of the contact force between the particles and the kinematics equation of the particle model were deduced. The coupling simulation of computational fluid dynamics and discrete element method (CFD-DEM) was adopted to simulate the gas-solid two-phase flow in the cleaning chamber in order to obtain the trajectory of the particles, where the SIMPLE method was used to simulate the gas phase, and the particle trajectory model was used to simulate the solid phase. The simulation results indicate that the airflow in the cleaning chamber presents a certain delamination where the airflow near the top and bottom walls has lower velocity than that passing through the mid-chamber and the airflow distribution in each layer is stable without obvious vortex. Each grain component has respective particle trajectory which is significantly different. This indicates that effective separation on each grain component could be achieved in the novel grain separation unit. The experiments on the material movement trajectory during the grain separation process were executed under two sets of conditions and the distribution of the grain, chaff and straw pieces at different moments was shot by high-speed camera. The Blaster’s MAS software was used to track the particle trajectory. By comparing the experimental trajectory with the simulated trajectory calculated from the CFD-DEM model, it is found the simulated results are mostly in accordance with the experimental ones, which verifies the feasibility of the CFD-DEM model.