Design and experiment on handheld air-assisted pollination device

Abstract: Pollination is a very important process for high yield and quality of fruits production. The artificial and bee pollinations are wildly used in fruits production, but they are unadaptable to large scale production. So a kind of handheld air-assisted pollination device was developed. Through theoretical calculation, the air supply device was determined to adopt 6 impellers, the impeller diameter is 38 mm and the guide blades width is 18 mm. The motor is driven by DC power. A wind velocity indicator was used and the test ring was put at 500 mm ahead of the air inlet which is connected with a set of rams to fan pipes. The ram's diameter is 38 mm, same as the impeller. The results of fan performance test showed that the air volume was 3.0?10-3 m3/s at 8 000 r/min of fan speed, which can meet the design requirements. The highest total pressure efficiency is 43% at 9 000 r/min of fan speed. With the speed increase, the total pressure efficiency dropped rapidly but the power increased and the variation trends of the air volume and air pressure are not significant. The fan property was tested and the performance curve graphic was drawn. The air velocity field at different rotational speeds of the handheld air-assisted pollination device were studied and validated by the experiment data. The results showed that the velocity of central plane diffused at a fixed angle and decayed along the centre line, and the theoratical values closely related to the experiment data. In order to study the effect of airflow speed on pollination, the basic principle of pneumatic pollination was analyzed. Tests were conducted to validate the effect of airflow speed on pollens distribution based on pollens density, horizontal distribution and vertical distribution in the lab. The results show that the flow rate of nozzle is affected by wind velocity significantly. When the winds velocity reaches 25 m/s, the variation trends of the flow rate of nozzle are not significant with the speed increase. And the pollens distribution is affected by wind velocity significantly, and the dusting rate on horizontal and vertical distribution increase with the wind velocity increase. A peak in horizontal and vertical distribution is far away from the pollen source with the wind velocity increased. And the peak in vertical distribution keeps stable within a certain distance, which suggests that the pollens can be spread in straight line with a certain speed and directional airflow. The field experiment was conducted in a kiwi grove which was grown with "Hongyang" kiwi trees. The row space is 3 m×2 m, the height of the tree is 1.8 m. Three trees were randomly selected as sample trees, 10 flowers were selected in each tree, and the distance of pollination is 15-20 cm. The pollen coverage ratio of stigma in each flower was measured by micro camera and droplets image processing system. The results show that the pollen coverage increases significantly with the increase of the fan speed. When the nozzle outlet velocity is 19.5 m/s, the pollen coverage is 57.66%. The research can provide a reference for structural design and optimization of working parameters in same type device.