Design and parameter optimization of cotton tip polarization-electrostatic spraying system based on high voltage electrostatic field

Cotton is one of the main raw materials in the global textile industry. Its output and quality have a significant impact on the market supply and demand, as well as international trade. Among them, the chemical defoliation and topping techniques have been widely applied to increase the cotton production. But there is the increasingly prominent pollution of the soil, water source and ecosystem. Electrostatic spraying can be expected to enhance the adhesion of the liquid droplets for the uniform coverage of the crops. However, the existing technologies have been confined to the large droplet size and low adhesion rate, resulting in only 40.6% effective utilization of the pesticides for the serious waste of resources. In this study, a cotton tip polarization-electrostatic spraying was proposed to optimize the chemical topping and defoliation spraying, according to the high-voltage electrostatic hetero-charge adsorption. The utilization rate of the pesticides was then improved to reduce the environmental pollution. Firstly, a systematic simulation was performed on the charge migration during polarization of cotton tips using COMSOL Multiphysics software. The feasibility of cotton tip charging was also verified after simulation. Subsequently, a cotton tip polarization-electrostatic spraying system was designed and then built. Two devices consisted of an electrostatic spraying and a cotton tip polarization. The opposite charges were induced on the cotton tip surface and the droplets in a high-voltage electrostatic field, in order to enhance the electrostatic adsorption force. The water-sensitive experiment was used to replace the cotton leaves for the measurement of droplet adhesion rate and particle size. The deposition behavior of the droplets on the leaf surface was also observed using high-speed camera. Design-Expert 13 software was also utilized to optimize the parameters, including the optimal combination of the polarization voltage and droplet charging voltage. The experimental results show that the polarization treatment of the cotton tips was significantly improved the deposition of droplets. The leaf charge decay was divided into the rapid and slow stages. The stable state lasted for more than 30 min, providing for an effective time window during electrostatic spraying. Under the optimal combination of the parameters (polarization voltage 15.4 kV, and droplet charging voltage 20.3 kV), the droplet adhesion rate reached 43.08%, which was 51.40% higher than that of the single electrostatic spraying. At the same time, the median diameter of the droplet volume decreased by 2.36%. High-speed camera analysis further confirmed that the polarization of the cotton leaves made the droplet movement more linear, thus enhancing the leaf's adsorption capacity for droplets. An adhesion rate was as high as 89.54%, significantly better than the 70.95% of the traditional. This finding can provide the new ideas to optimize the cotton tip polarization with the electrostatic spraying. The utilization rate of pesticides can be effectively improved to reduce the environmental pollution. Technical references can offer for the green production of different cash crops.