Design And Flow Analysis On Pneumatic System Of Seedlings To Target Sprayer

Nursery and fruit trees are characterized by a large variety of tree types and large tree spacing.Less than 30% of conventional sprayed pesticides can be deposited on the canopy,and large amounts of liquid chemicals are lost to the ground or float to the air.There are outstanding problems such as low utilization of liquid medicine,serious waste of pesticides,and pollution of the environment.The air-assisted spray technology uses the high speed airflow generated by the fan to atomize and deliver the droplets to the target,which increases the penetration of the droplets and effectively reduces droplet drift.With the continuous improvement of environmental protection requirements,a seedlings to target sprayer with the characteristics of target profiling spray is widely used,but its pneumatic system still lacks relevant structural optimization research.Compared with other types of air-assisted sprayers,the advantages of airflow velocity and spray range are not significant.In this thesis,the structural design and flow field analysis of the pneumatic system of the seedlings to target sprayer is completed,the selection of the centrifugal fan is completed,and the air duct bracket,multi-outlet device and air duct pipeline are designed.Focusing on the numerical simulation analysis of the internal flow field of multi-outlet devices and air duct pipelines,studying the structural features of the pneumatic system that are conducive to air flow transmission,and combining the tests of wind speed,wind pressure and spray distance on the air flow field inside and outside the pneumatic system.The specific air flow transmission performance of different pneumatic systems is compared and analyzed,and the distribution of air flow fields is studied.The main research contents and analysis results of this thesis are as follows:(1)The overall structure of the pneumatic system is designed,and the air duct bracket is analyzed for reliability.Through numerical simulations,the main design points of the multi-outlet device and the air duct pipeline structure are as follows: The outlet position should avoid excessive deflection angle with the direction of the incident air flow;The internal flow passage structure which volume is gradually reduced along the air flow direction is more favorable for the air flow transmission;The outlet passages should be arranged compactly to prevent the air flow from flowing back due to the flow passage blocking;After the ducts diverge,the airflow velocity in each branch duct will be changed,the more the number of divergences,the greater the difference in the wind speed at the outlet of each duct;The angle of the diverging can not be too large to prevent local turbulence;Ducts should avoid bending as much as possible to keep the airflow smooth.(2)Conducting numerical simulation analysis and comparison of the internal airflow fields of different pneumatic systems.The rotation speed of the fan has little influence on the airflow velocity distribution inside the pneumatic system;The higher wind speed at the outlets ofmulti-outlet device appear at the middle and right outlets of the front row,and the lower wind speed appear at the left side of the front row and the right outlet of the rear row.The distribution of wind speed at the outlets of F-?-6 device is the most uniform,and the difference in the wind speed at the outlets of A-?-8 device is the largest.(3)The data of wind speed and wind pressure at the outlet of the centrifugal fan,the outlet of the multi-outlet device,and the outlet of the air duct of different pneumatic systems are analyzed.Under the same fan speed,the wind speed distribution at the outlets of F-?-6 device is the most uniform.The distribution of wind speed at the outlet of each outlet of D-?-8 pneumatic system is the largest,and there is little difference in the wind speed distribution between F-?-6device and A-?-8 device;The air duct wind pressure loss rate of the D-?-8 pneumatic system is the lowest,and the wind speed at the outlet of the air duct is negatively correlated with the wind pressure loss rate;The shorter the duct length,the lower the wind pressure loss rate,and the smaller the influence of the duct on the outlet wind speed;With the same pneumatic system,as the fan speed increases,the difference in the distribution of wind speed at the outlets of the air ducts tends to increase.(4)Conducting comparison and analysis of velocity distribution and spray distance test data of single air duct and multi-duct outer flow field of pneumatic systems.The spray distance of the outer flow field of the single air duct is affected by the wind speed at the outlet of the air duct,and the vertical width boundary of the air flow is independent of the wind speed at the outlet of the air duct;In the multi-duct external flow field,under the superposition of the air flow of each duct,the airflow energy becomes larger,and the speed of wind speed attenuation is slower;In the same air duct height interval and fan speed,although the overall wind speed of the eight outlets pneumatic system is lower than that of the six outlets,the airflow field covers a wider range;The difference of airflow velocity at different heights shows a narrowing trend with increasing spray distance,and the overall airflow velocity tends to be uniform;The advantages of high wind speed at the outlet of the F-?-6 pneumatic system will gradually decrease as the spray distance increases,the wind speed of the airflow field at the eight outlets pneumatic system is basically the same after 3m.The more air ducts,the greater wind speed boundary range of the multi-duct outer flow field.