Numerical Simulation And Experimental Study Of Negative Pressure Cleaning And Grading Device

Harvest crops,often contain more impurities and crops such as peanuts,jujube,peppers also inevitably mixed with immature,damaged,plant diseases and insect pests of fruit.If not handled in time,it will greatly affect the economic benefits of growers and it easily cause the decay of crops in the process of storage and transportation.Therefore,it is an important link to remove impurities and grade the harvested crops.At present,most of the crop cleaning devices with good cleaning and impurity removal effect adopt the mode of wind-screen combination and the devices have the defects of large size,heavy weight,difficult maintenance,high cost and so on.The classification of crops is still mainly by manual selection.Therefore,a new type of negative pressure air separation device is designed based on the Laval nozzle structure principle.The air flow blown into the air duct by the fan generates a certain negative pressure in the negative pressure pipe and the crop is separated under the action of the negative pressure lifting force of the air flow in the negative pressure pipe.The whole negative pressure sorting process does not generate dust or damage crop fruits and the device has the advantages of simple operation,easy maintenance,small size,high automation degree,low cost and the like.The main work and conclusions are as follows:(1)The structure of the negative pressure air separation device is designed by analyzing the fluid flow energy loss in the pipeline.In order to improve the utilization rate of energy and the vacuum degree of negative pressure tube can be precisely controlled,the structure optimization of the negative pressure air separation device is carried out based on the fluid simulation software Fluent.The value of each factor is determined based on the single factor and five factor and three level experiments and the structure size of the negative pressure grading device based on Laval nozzle is determined.(2)The flow field of the negative pressure grading device is simulated based on the software Fluent.The relationship between the velocity of the active inlet and the passive inlet and the pressure distribution in the negative pressure pipe mouth and negative pressure pipe are analyzed.Taking the light-weight regular cylinder as the experimental object,the change of the negative pressure lifting force in the negative pressure tube is analyzed with different heights in the negative pressure tube,the upwind section area,the length of the negative pressure tube as the variable.The law of change of the negative pressure lifting force in negative pressure tubes with different heights is verified by taking peanut as the experimental object.(3)The negative pressure separation process of high quality and inferior grade peanuts is simulated based on CFD-DEM coupling simulation.According to the stress situation in the process of peanut negative pressure separation,the contact mechanical model between peanut and air duct is selected,the peanut particle model is established by using the method of multiple spherical surfaces combination.The difference between the movement speed and the lifting force of high quality and inferior peanuts in the negative pressure tube is analyzed.In order to discuss the effect of the ratio of the windward area and the diameter of the pipe to the negative pressure lifting force,the spherical model is used to analyze the resultant force changes in pipes with different diameters when the intake velocity is constant.(4)Taking the long pepper in the pepper as the test object,a negative pressure air separation device suitable for impurity removal of hot pepper is designed based on the structure of negative pressure air separation device and relying on hot pepper feeding device,the negative pressure impurity removal test of pepper is carried out to verify the impurity removal effect of the device.The negative pressure grading device is used to carry out negative pressure grading test for peanuts with a small difference in quality based on the simulation and optimization of Fluent.The peanut grading test is carried out with taking the speed of the conveyer belt,the height of peanut and the inlet speed of the air duct as the experimental variables by setting up a simple conveyer table and the influence of three variables on the grading effect of peanut is obtained.