超大颗粒肥水田气力深施加速器设计及参数优化

为解决水稻撒施追肥存在的肥料流失、利用率低及机械深施肥工作部件易堵塞、伤根等问题，该研究设计了一种用于水田深施追肥机的超大颗粒肥气力式加速器。该加速器利用双螺旋高压气流，在其与肥料上端构成的近封闭空间内加速超大颗粒肥，实现其高速射入泥壤，并可避免肥料颗粒与管壁碰撞；出口设置渐扩管扩散气流，可减轻对泥壤的冲击，提高施肥位置的稳定性。根据超大颗粒肥参数与加速器功能要求，确定了加速器的结构参数，并根据肥料入泥深度所需的射出速度，分析确定了加速器的工作参数。在此基础上，基于Fluent软件的六自由度重叠动网格建立了加速器仿真模型，以进口气流速度、螺旋角和加速管直径为试验因素，进行单因素仿真试验与三因素三水平Box Behnken组合仿真试验，研究各因素对肥料射出速度与气流扩散率的影响。多因素试验分析及响应面分析结果表明，加速器的最佳工作参数为进口气流速度47 m/s、加速管直径21 mm、螺旋进气口螺旋角43°。在此条件下进行台架验证试验，得到肥料射出速度均值为12.61 m/s，出口气流扩散率均值为85.5%，肥料入泥平均深度为4.68 cm，达到了水稻追肥要求。该研究可为超大颗粒肥水田气力深施追肥机设计提供参考。

Design and parameter optimization of the accelerator for pneumatic deep application of super-large fertilizer granule in paddy field

Topdressing has been widely used to supplement the basic fertilizer in the middle and later growing stages in paddy fields. Broadcasting is one of the fertilizer applications to meet the nutritional needs of rice. The commonly used broadcasted fertilizer may flow with the surface water in rice production, resulting in environmental pollution, fertilizer loss and a low utilization rate. And a furrow opener in the most deep fertilization machine can result in the blockage of the working parts and damage to plant roots. In this study, a Super-large Fertilizer Granule (SFG) accelerator was designed for deep fertilization in the paddy field, in order to reduce the fertilizer loss with a high utilization rate. The high speed of the SFG was achieved in the release and long-term effectiveness of SFG. The high-pressure airflow was formed at the twin spiral inlet within an approximately closed space in the acceleration tube above the SFG. The SFG was accelerated to avoid the collision of the SFG on the wall of the accelerator tube as well, in order to reduce the speed loss of the SFG; The airflow was diffused at the outlet to reduce its speed and the impact on the soil, in order to improve the stability of fertilizer position. The structural parameters of the accelerator were determined using the physical parameters of SFG. The working parameters of the accelerator were analyzed to fully meet the requirement of the injection speed for the depth of fertilization. A simulation model was established for the accelerator using the Fluent platform. 6DOF overlapping dynamic grid was selected to simulate the flow field in the accelerating tube in the fluid domain. The single-factor experiments and three-factor three-level Box Behnken combination experiments were conducted with the inlet airflow speed, inlet spiral angle, and acceleration cylinder diameter as the experimental factors. A systematic investigation was implemented to explore the effects of the factors on the injection speed of fertilizer and the diffusion rate of outlet airflow. The regression model and response surface analysis of the test indexes were established by multifactor experimental analysis. The results showed the optimal working parameters were achieved in the accelerator: inlet airflow speed of 47 m/s, acceleration cylinder diameter of 21 mm, and spiral inlet angle of 43°, when the weight of the accelerator fertilizer injection speed was 0.6, and the weight of the outlet airflow diffusion rate was 0.4. The bench test was carried out using the 3D-printed SFG spiral accelerator, where the SFG was developed by Shenyang Agricultural University Rice Research Institute. The average fertilizer ejection velocity was measured to be 12.61 m/s, the average diffusion rate of outlet airflow was 85.5%, and the average depth of fertilizer into the soil was 4.68 cm, thus meeting the requirements for the deep fertilization of rice. There was a small relative error between the predicted value from the multi-factor regression and the experimental, indicating the more accurate optimization of the simulation test. This finding can provide a promising basis for designing the pneumatic machines of deep application for the super-large fertilizer granule in paddy fields.