The Study Of Air Flow Field Of A Cylindrical Screen Cleaning Device

The airflow field in the cylindrical screen cleaning device plays a role in clearing light debris,improving grain trajectory in the sieve and easing grain accumulation,so it would be beneficial to improve the quality of cleaning by studying and optimizing the airflow field distribution.On the basis of investigated the physical properties of the grain,the flow field in the cylinder screen cleaning device was simulated and experimented in this thesis.The main conclusions included.(1)Some physical characteristics of each component of extractions was measured,such as triaxial size,moisture content,grain weight and suspension speed.The analysis revealed that there are some differences between physical characteristics of each component of extractions,especially the suspension speed of extractions.The suspension velocitys of grain,the empty grain and short stem are 9.77m/s-12.86m/s,4.23m/s-6.77m/s,5.36m/s-6.5m/s,respectively.This provided a reference for the study of the grain screen.(2)In this thesis,a multifactorial adjustable cylinder screen in the laboratory was taken as research object.The three-dimensional model of a cylindrical screen was established.The CFD software Fluent was used to calculating the flow field model.The finding by analysis is that:The air velocity is lower near the wall of cylinder screen.Along axis direction of cylindrical screen,air velocity of each point decreased obviously.Back in the cylinder screen,distribution of air is more uniform,air velocity of each point is smaller in the circumferential surface of cylindrical screen;Influenced by feeding plate,the highest air velocity is not in the center of the cross section on cylindrical screen,and a small area of backflow region is located in the front of cylinder screen and the middle-lower position of expanding duct exit.(3)Using Fluent software to simulate the air flow field based on different fan speed,the diameter of the cylindrical screen and the diameter of expansion duct outlet.The effects of these parameters on air flow field were analyzed.The analysis shows that the fan speed and cylinder diameter have a greater impact on air fleid distribution,while the diameter of expanding duct outlet has less effect on the flow field.(4)Setting the discrete phase of a multiphase flow is based on the physical properties of measurement of rice,the Lagrange method is used to simulate and analyze of the distribution of threshed materials(mainly for shriveled grain and grain).(5)Evaluation index is based on the center of cylinder entrance(A point)of air velocity,inspected the impact of the cylinder diameter,the rotating speed of centrifugal fan and expanding duct exit diameter on flow field through three factors and three levels orthogonal experiment.According to the scope of evaluation index,the best parameter combination for cleaning is found by using the analytic method.The fan speed is 2100 r/min,cylinder diameter is 250mm and expanding duct exit diameter is 400mm.And using variance analysis examined the impact of factors on the evaluation index.Centrifugal fan rotational speed and the cylinder diameter has a significant influence to airflow velocity of A point,the export expansion duct diameter had no significant effect to airflow velocity of A point.(6)Air velocity at different points in the cylinder screen has been measured by the way of setting points in the sieve,and the effects on airflow field of different fan speed has been compared.The flow velocity at each point from experiments was compared with the numerical simulation by using Fluent software,and analysised the reliability of the numerical results by using t-test,it could be concluded that there's no evident difference between the experiment and the simulative results.