Design And Working Mechanism Of Air-assisted Centralized Metering Device For Rapeseed And Wheat

Rapeseed and wheat are important oil plant and food supply in the middle-lower Yangtze area in China.They are grown in the same season and their sowing dates and mechanized seeding processes are closer.The precision planter has performance with precision seeding,high speed,good generality and high efficiency.Air-assisted centralized pneumatic planter which could be widely used in seeding is capable of handling a wide range of seeds with different sizes and shapes during travelling at high operating speed.Based on material properties for both rapeseed and wheat seed,the staggered arrangement model-hole and combined conical-hole unit which realize adjustment of seed feed rate in wide range for rapeseed and wheat were designed.The seed distribution performance of bowl-type distributor was good.The methods of kinetics analysis,DEM-CFD coupling approach and high speed photography were utilized to analyze the working mechanism including centralized metering system’s airflow field,seed motion and movement trajectory.The main research results were as follows:(1)According to the material properties and unit area’s seeding quantity of agronomic requirements,overall program of air-assisted centralized metering device based on seed feeding from mechanism and seeds’ distribution from airflow was carried out.The structure composition and working principle of centralized metering device were illustrated.The structures of core parts of centralized metering device including seed feed device,seed feeding device,seed conveying tube,pressurized tube,distributor and seed tube were determined.(2)The main components’ structure and parameters of air-assisted centralized metering device were designed and analyzed.The seed feed device for rapeseed and wheat with staggered arrangement model-hole and combined conical-hole unit was designed.This research determined main structural parameters of model-hole and conical-hole unit.The diameter of conical-hole unit was 80 mm.The length,width,depth and cone angle of model-hole were 8.0 mm,5.0 mm,4.0 mm and 14°,respectively.The sum of conical-hole unit and blank unit was 6.The range of seed feed rate which adjusted to different sowing width and operating speed was changed by No.of conical-hole unit and rotational speed for rapeseed and wheat.Seed feeding device based on Venturi theory was designed and the diameter of two-phase flow outlet tube was 42 mm.Besides,the corrugated pressurized tube and bowl-type distributor were designed and main structural parameters were determined.According to the airflow requirement and air pressure loss,air pump’s flow rate and air pressure was 115.16 m3/h and 1.96 kPa,respectively.The HG-1100 type vortex air pump was chosen as pump of air-assisted centralized metering device.(3)The seed filling mechanism of air-assisted centralized metering device was analyzed and the mechanical models of seed in seed filling and feed process were established.It demonstrated that seeds filling and throwing with inclined angle(θ)model-hole were easier and the optimal inclined angle(θ)was from 13.75° to 21.20°.While rotational speed of seed feed device was 10-30 r/min,seed feed performance of conical model-hole with 20° inclined angle was better than that of other model-hole.The coefficient of variation of seed feed rate stability of rapeseed and wheat was not more than 1.00% and 1.10%,respectively.With the increase of rotational speed in the range of 10-60 r/min,seed feed rate increased significantly,while the coefficient of variation of seed feed rate stability decreased and then raised up.Thus,the optimal rotational speed of rapeseed and wheat was 10-40 r/min and 20-50 r/min,respectively.By changing No.of conical-hole unit and rotational speed,the range of seed feed rate gained of seed feed device for rapeseed and wheat was 28-450 g/min and 95-770 g/min,respectively.The structure of seed feed device can realize adjustment of seed feed rate in wide range for rapeseed and wheat.(4)In order to analyze effects of seed thickness on seed movement and seed feed performance,EDEM software was utilized to simulate the filling performance and high speed camera technology was used for executing the experiment.It was observed that seeds’ compressive force,seed filling angle and feeding performance of regulating plate with 60° were found to be better than that of others parameters.Seeds’ compressive and tangential force increased with the increase of longitudinal distance and decrease of lateral distance.When rotational speed was within the range of 10-50 r/min,seed initial filling angle,filling angle and seed feed rate raised with increasing of longitudinal distance and decreasing lateral distance.In addition,the coefficient of variation of seed feed rate stability decreased and then raised up with increasing longitudinal distance and the decreasing of lateral distance.Effects of seed layer thickness and rotational speed on seed filling angle mainly resulted from compressive force and tangential force,respectively.The ideal parameters were longitudinal distance of 15 and 20 mm for rapeseed and wheat and lateral distance of 46 mm.Under the combination condition of optimum seeds layer thickness,seed filling and feed performance were good for both rapeseed and wheat seed.(5)In order to improve wheat seeds’ filling performance,seed churning device as a part of seed feed device was designed.It was observed that seed feed device with churning device gave superior filling performance at all treatments by increasing seeds’ compressive force,tangential force,number of seeds in model-hole,filling angle and seed filling rate.Seed churning tooth’s length affected filling angle and No.of seeds in each model-hole significantly and No.of seeds in each model-hole was different significantly among arrangements of churning tooth.The ranking orders of factors affecting filling angle and No.of seeds each model-hole were: churning tooth’s length > arrangements of churning tooth > churning tooth’s shape.The seed feed device with a churning tooth’s shape of cylinder,a churning tooth’s length of 6 mm,and a arrangements of churning tooth of double helix produced superior results with a filling angle of 78.20°,a No.of seeds each model-hole of 1.73,recording a coefficient of variation in No.of seeds each model-hole of 0.69%.Under the conditions of a rotation ratio between seed churning device and feeding mechanism of 1.154 and a No.of conical-hole unit of 6,seed feed rate and its coefficient of variation were 690-1340 g/min and 0.23-0.80% with rotational speed of 20-40 r/min,respectively.(6)A numerical study of gas-solid flow of mixing and transport processes in air-assisted centralized metering device was carried out by means of Discrete Element Method(DEM)and Computational Fluid Dynamics(CFD)coupling approach.Effects of structural parameters of seed feeding device and seed conveying tube on airflow field and seed movement were studied and analyzed.Simulation results showed that,seed velocity of airflow direction which resulted from drag force.The increase of throat area resulted in the decrease of seed velocity and pressure loss in a certain range.Seeds moved slowly and generated the phenomenon of bounce and concentration for low airflow inlet velocities.With the airflow inlet velocity increased,resultant force and seed velocity developed.The seed velocity in seed conveying tube’s outlet increased first and then decreased with increasing ratio between lateral length and longitudinal length(k).When seed conveying tube’s diameter,length and k was 42 mm,1.0 m and 2/3,seed velocity,the relative velocity between particle and airflow and seed distribution were good with lower pressure loss and better seeding performance.Seed velocity of conveying tube with bends was larger than that of conveying tube with mansard joint.Airflow field and seed distribution was uniform with larger seed velocity and lower pressure loss in conveying tube with bends of 100 mm of radius.(7)The distribution mechanism of air-assisted centralized metering device was analyzed based on DEM and CFD coupling approach and the structural parameters were optimized.Effects of corrugated pressurized tube’s structural parameters including dimple depth,dimple pitch and length of pressurized tube on variation coefficient of seed distribution and variation coefficient of seeds’ distribution uniformity were studied.Optimization of the regression equations incorporating dimple depth,dimple pitch and length of pressurized tube through multi-objective programming revealed that a dimple depth of 4.2 mm,dimple pitch of 15 mm and length of pressurized tube of 180 mm.Based on the optimized operational parameters,variation coefficient of seed distribution and variation coefficient of seeds’ distribution uniformity were 91.17% and 4.91%,respectively.The seed movement trajectory and seed distribution status in distributor were obtained.Seed velocity decreased with the increase of inclined angle.When the outlet tube’s diameter of distributor’s streamline tube were 16 mm and 60°,airflow velocity,seed motion and seed distribution uniformity were better.Seed resultant force and velocity increased first and then decreased with increasing radius of streamline tube’s datum line.Apiece row consistency variation coefficient which of 120°was smallest decreased first and then increased with the increase of cone angle of distributor’s cover.(8)Seeding performance experiments of air-assisted centralized metering device were carried out.Effects of seed tube’s parameters including seed tube’s material,diameter and arrangement and working parameters of centralized metering device on seeding performance were investigated.Experimental results indicated that seed tube with PVC bellows material and diameter of 20 mm and the same length of seed tubes were benefit to seeding performance.When the air pressure was 1200 Pa and 1600 Pa of rapeseed and wheat,apiece row consistency variation coefficient of seeding quantity were both less than 4.00%.The seeding quantity was 20.92~22.76 and 52.92~56.32 in each meter for rapeseed and wheat,respectively.The variation coefficient of seeding uniformity,stability of full seeding quantity and seed damage rate were no more than 20.00%,0.80% and 0.15%,respectively for both rapeseed and wheat.(9)The field experiment was performed using Huayouza 62 and Zhengmai 9023 as materials during year 2015-2017.Experiments results demonstrated that plant density was 38-80 plants per square meter and their coefficient of variation was less than 20.00% for rapeseed.Plants’ distribution was 118-143 and 232-278 plants per square meter under two seeding quantity treatments and their coefficient of variation was about 8.00%.Effects of sowing date and sowing quantity on growing characteristics and yield were illustrated split plot field experiment.Experiments results indicated that plant individual quality became weaker with delaying sowing date and increasing sowing quantity.Moreover,the yield for rapeseed and wheat was 2900 and 6800 kg per ha,respectively.Thus,we suggest that developing the seeding uniformity of air-assisted centralized metering device,choosing proper sowing quantity and sowing date and optimizing field management is to achieve whole and strong seedlings once.We should sow seeds early after harvesting rice in proper sowing date and the proper plant density was 30×104-45×104 plants per ha.Increasing sowing quantity can optimize plants structure in late sowing date condition and the proper plant density was 50×104-60×104 plants per ha for rapeseed.Innovation point 1: The combination technique of seed feed device with oblique cone wheel conical-hole unit and bowl-type distributor was proposed and air-assisted centralized metering device for both rapeseed and wheat was designed.Innovation point 2: Inclined cone-shaped model-hole and staggered arrangement’s conical-hole unit were designed,which realized to adjustment of seed sowing rate in wide range for rapeseed and wheat.