Optimization of the structural parameters of pollination pipe for pneumatic hybrid rice breeding pollination machines

Abstract: Hybrid rice has made outstanding contributions to solving the world's food problems, and seed production is a key link in the production of hybrid rice. In response to the current urgent need for mechanized pollination equipment for hybrid rice production, a pneumatic hybrid rice pollination machine was designed, it is mainly composed of power chassis, battery, controller, air velocity transducer, side pollination, middle pollination pipe, central pollination pipe, fan and lifting part. Firstly, a computational fluid dynamics model was established for its key component pollination pipe, the structure of the pollination pipe includes inlet, body, deflect, outlet and divider. Moreover, in order to explore the law of flow field distribution of pollination pipe, a single factor experiment was designed, with the diameter of pollination pipe, outlet length and outlet width as factors. The experiment results showed that with the increase of diameter of pollination pipe and the decrease of outlet length and width, the acute angle between the direction of the external airflow and the centerline of the pollination pipe increased, which was consistent with the requirement that the airflow was far as possible perpendicular to the center of the pipe during pollination. The better range of pollination pipe structure parameters was that diameter of pollination pipe was greater than 70 mm, and outlet length and width were 100-150 and 4-8 mm respectively. Furthermore, a three-factor and three-level Box-Behnken simulation experiment was designed taking the variable coefficient of airflow velocity and cover height of airflow as targets with Design Expert software to obtain better pollination pipe structure parameters, and the parameters of the pollination pipe structure were optimized. The results showed that the range of diameter of pollination pipe from 60 mm to 80 mm, outlet length from 100 mm to 200 mm, outlet width from 4 mm to 10 mm, diameter of pollination pipe, outlet width and interaction between diameter of pollination pipe and outlet width, outlet length and outlet width, square of outlet width had significant effects on variable coefficient of airflow velocity, and the influences of various factors on it as follows from large to small were square of the outlet width, interaction between diameter of pollination pipe and outlet width, interaction between outlet length and outlet width, diameter of pollination pipe, outlet width, square of diameter of pollination pipe, outlet length; diameter of pollination pipe, outlet length, outlet width and their interaction between outlet length and outlet width, diameter of pollination pipe and outlet width has a significant effect on cover height of airflow, influence of various factors on it as follows from large to small is outlet width, diameter of pollination pipe, outlet length, interaction between outlet length and outlet width, diameter of pollination pipe and outlet length. The optimization of structure parameters of pollination pipe was that diameter of pollination pipe 64.49 mm, outlet length and width was 200 and 7.25 mm, the variable coefficient of airflow velocity was 9.10% at this condition, and cover height of airflow was 187.57 mm. In order to facilitate processing, a standard pollination pipe with an inner diameter of 61.5 mm was selected, and outlet length and width were 200 and 7.5 mm respectively for verification experiments. The measured value of the air outlet flow velocity was basically the same as the simulation value, the measured variable coefficient of airflow velocity was 8.83%~9.25%, and the cover height of airflow was evenly distributed. The research results can provide a theoretical reference for the optimization of the parameters of the pneumatic hybrid rice seed production pollination machine.