Design And Analysis Of Key Components Of Wheat Seed Metering System

With the large-scale planting of wheat in northern China,the traditional mechanical planter has been unable to meet the actual production needs,there is an urgent need for stable large-scale,wide-width and high-speed planter to improve operation efficiency.In this paper,the wheat airflow metering system is studied,and the key components such as corrugated guide tube and bionic distributor are designed,combined with gas-solid two-phase flow coupling method,bulk theory and high-speed camera technology.The motion characteristics and migration trajectories of wheat seeds in the metering system were studied to reveal the working mechanism of wheat seeds in the metering system.The simulation software is used to analyze the internal flow field distribution and seed movement law of the air transport seed metering system,so as to determine the influence of seed pipe length on the seed metering performance,and verify the seed metering performance of the seed metering system by bench test.The main research work of this paper is as follows:1.The physical parameters and mechanical properties of wheat seeds were determined.The bulk density,moisture content,1000-grain weight,triaxial size,equivalent diameter,sphericity and suspension speed of wheat seeds were 737.66g/L,10.32%,56.51 g,6.10mm×2.99mm×3.29mm,3.92mm,0.64 and 11.79m/s respectively.The simulation model is established according to the wheat seed parameters,and the rationality of the wheat seed model is verified by EDEM simulation and bench test.The relative error between the simulation value and the test value of the seed quality discharged by the centralized seed metering device under different working length of the pulley is in the range of 3.08%-7.82%,indicating that the model can fully reflect the motion and mechanical characteristics of the seed.2.The structure design and optimization of the guide tube in the air conveying seed metering system are carried out.According to the influence of the structure of the diversion tube on the uniformity of seed distribution in the seed metering system,the motion attitude and motion law of wheat seeds in the diversion tube were studied by means of gas-solid two-phase flow coupling simulation,and the mechanism affecting the uniformity and distribution uniformity of gas-solid two-phase flow was revealed.The effects of different structure of guide tube on seed distribution uniformity,pressure loss and consistency variation coefficient of displacement in each row were analyzed by orthogonal test,and the structure of guide tube was further optimized.It was obtained that the optimal parameter combination of guide tube was 800mm,ripple depth 8mm,ripple number 6 and ripple width 50mm.The optimized airflow velocity in the guide tube was uniform and basically eliminated turbulence,and the pressure loss was small.Through the bench test,it is proved that the consistency variation coefficient of each row displacement of the diversion tube structure under different inlet air velocity and sowing rate meets the standard requirements and meets the actual production requirements.3.Based on the bionic principle,according to the streamline curve of crucian carp,the bionic crucian carp curve distributor is designed,and the pressure loss mechanism of the distributor is analyzed.The working pressure loss,turbulence and seed distribution uniformity of four bionic distributors and the original structure distributor are simulated and analyzed by using the coupling method of EDEM and Fluent,and the optimal structure of bionic distributor is determined.Through the bench test,it is found that the consistency variation coefficient of each row displacement of the bionic optimized distributor is smaller than that of similar products at home and abroad,and the pressure loss of the distributor is small,indicating that the distributor can effectively reduce the pressure loss,improve the seed distribution uniformity of the air transport seed metering system and improve the seed metering performance.4.The working mechanism of seeds in seed transporting pipe is revealed by theoretical analysis,gas-solid two-phase flow coupling simulation and bench test.According to the theoretical analysis,the influence of the length of the seed pipe on the average flow velocity in the pipe is obtained.When the seed pipe is shorter,the decrease of the average velocity is more obvious,and when the length of the pipe is larger than a certain length,the decrease of the average velocity tends to be smooth.Combined with EDEM-Fluent coupling simulation and high-speed camera technology to measure the seed velocity in the transporting tube,by comparing the simulation and test results,the average correction coefficient of seed velocity in the transporting tube is 0.95,which verifies the feasibility of the coupling simulation method for measuring the seed velocity in the transporting tube.5.An experimental study on the airflow conveying seed metering system was carried out through the bench test.Taking the consistency variation coefficient of each row discharge and the stability variation coefficient of the total discharge as the evaluation index,the effects of working parameters such as air volume,sowing rate and seed pipe length on the seed metering performance were analyzed.Through the response surface analysis,it is found that the corresponding range of sowing rate to make the variation coefficient of total displacement stability and the consistency variation coefficient of each row displacement stable is 198.8kg/hm2-270kg/hm2,air volume is 7.92m3/min-8.55m3/min,and the length of seed pipe should be more than 3.02m.Through the verification test of the combination range of parameters,the coefficient of variation of total displacement stability is 0.43%-0.54%,the coefficient of consistent variation of each row's discharge is 2.71%-2.91%,and the seed fragmentation rate is 0.39%-0.42%,which meets the requirements of relevant standards.