风送静电喷雾中雾滴在果树冠层沉积机理研究

The air-assisted electrostatic spray is one of most efficient pesticide application for orchard pest control. Dynamic characteristics of charged droplets deposition in fruit tree canopy effects the adhesion performance. But the action mechanism between droplet deposition and airflow, electrostatic field, canopy target were not clear. The existing researches on deposition and interaction mechanism mainly concentrated in test and qualitative analysis. In order to acquire the mathematical relation between charged droplet deposition and tree canopy, Based on electrostatic spray theory and gas-liquid two-phase flow theory, this research will analyze the effects of airflow and electrostatic field on droplet transportation according to the general equation of droplet transportation in flow field. We focus on the canopy influence relation on charged droplet transportation to acquire the interaction mathematical relation. Thus, we integrated the relation into mass and momentum equations of the general equation of droplet transportation in flow field as source term to establish charged droplet deposition model. On the basis of the above research, the spray deposition test, high speed photographic test, PIV particle velocity test and numerical analysis would be conducted to research the charged droplet deposition mechanism in tree canopy at different condition, which is to get the influence mechanism of charged droplet deposition and to acquire the technological approaches for promoting droplet adhesive rate. The research results of this project will provide theory basis for design and optimization of air-assisted electrostatic sprayer and constitute of relevant application operation standard.

风送静电喷雾是果树病虫害高效防治的最主要发展方向之一。荷电雾滴在果树冠层中沉积的动力学特性直接影响其附着性能，而雾滴沉积受气流场、静电场和冠层靶标的作用机理尚不明晰。现有的雾滴沉积及影响机理研究主要集中在试验测试与定性分析阶段，针对缺乏荷电雾滴在果树冠层沉积的数学描述现状，本项目以静电喷雾理论、气液两相流理论为基础，从荷电雾滴在流场中输运的通用动力学方程出发，分析流场、电场对雾滴输运的影响，重点研究果树冠层对荷电雾滴输运影响的数学关系；并以此为源项融入到荷电雾滴在气流场中输运的质量和动量瞬态方程中，以此建立荷电雾滴在果树冠层沉积的数学关系；同时融合喷雾沉积试验、高速摄影试验、PIV测试和数值分析等手段开展荷电雾滴在不同作业条件下的冠层沉积特性研究，探明荷电雾滴在冠层中沉积的影响机理和提升技术途径。该研究为风送静电喷雾机设计与相关施药作业标准制定提供理论依据。

风送静电喷雾是提高果树病虫害防治效率的主要技术之一，但荷电雾滴在果树冠层中沉积的动力学特性、雾滴在耦合流场中的沉积机理尚不明晰。本项目以静电喷雾理论、气液两相流理论为基础，从荷电雾滴在流场中输运的通用动力学方程出发，理论分析了耦合场对雾滴输运的影响，研究结果表明由于气流连续相的密度远远小于雾滴的密度，与气流曳力相比视质量力、热泳力都比较小，仅为气流曳力的10-3量级，只有在近壁面等回流区，Saffman升力才具有与气流曳力相同的量级，因此本研究主要考虑风送静电喷雾雾滴所受的曳力和静电力；建立了建立了喷雾气流衰减模型，模型显著性检验F值小于临界值；气流边界扩展模型的决定系数为0.9724。建立了2D激光雷达冠层扫描系统，研究了激光点云密度与叶面积指数之间的拟合关系，建立了正面和背面扫描时的LAI预测模型，F检验结果显示样本间存在显著性差异，且其模型的拟合优度均大于0.9。采用4因素3水平的中心组合设计与响应面分析方法，研究感应电压、风机频率、喷雾距离和喷雾压力对雾滴覆盖率的影响，以反正面雾滴覆盖率及其比值为响应值分别建立了二次回归模型。模型的决定系数分别为95.14%、93.68%、93.95%，相对误差分别为4%、9.25%、16.26%。荷电雾滴在果树冠层空间的沉积分布试验显示，作业速度是影响静电喷雾效果的一个重要因素,作业速度为0.52m/s和0.84m/s时静电喷雾的反面雾滴覆盖率分别提高了40%和17%，但对正面的雾滴覆盖密度基本没有影响，甚至略低于非静电喷雾；静电喷雾有助于抑制雾滴飘移，试验结果显示在5-12.5m的采样区域内，静电喷雾的的飘移量比非静电喷雾减少了18%。提出了荷电雾滴沉积的高敏感性及农药应用环境、作业对象的复杂性是静电喷雾技术应用的最大挑战，荷电量持留时间短、荷电雾滴易吸附在喷雾机及人体上是急需解决的难题。