| Pesticides hold great importance in the process of agricultural production and play an irreplaceable role in the control of diseases and pests.While liquid pesticides are being applied,drift loss must be accompanying along the process,and the evaporation is one of the main approaches for drift loss to take place.In recent years,one of the methods to reduce drift loss and evaporation is through using the adjuvants that are recommended by the country government.However,the mechanism and rules behind various kinds of adjuvants in reducing evaporation are still not fully revealed.To clarify the evaporation situation when fog droplets travel through space and to research the influence rules from adjuvants along the process,through the combination of experiments and modeling,this paper evaluates the effect of evaporation reduction from non-ionic surfactant silwet408,mineral oil type of adjuvant Maidao and vegetable oil type of adjuvant Beidatong,meanwhile,brings out an approximate calculation method for the spatial evaporation of fog droplet group,to understand the travel rules of fog droplets and to provide theoretical and data supports for a high efficiency usage of pesticides.The research and conclusion of this paper cover the following aspects:(1)Set up a small type of evaporation experiment platform,collected the images of droplet evaporation under different temperature and humidity conditions,obtained the diameter changes of liquid at different time through image processing system,through these,calculated the speed of evaporation of fog droplets and researched the influence rules from the environment and adjuvants.Firstly,compared the evaporation speeds of pure water in different environments with their theoretical values,picked the classic evaporation model Spalding as the model basis of the evaporation under the condition of pesticide spraying.Then,researched the scales of change and rules in water evaporation speeds from adjuvants under different environmental conditions,through the regression fitting,the calculation formula of the adjuvant factor was obtained and the influence mechanism of adjuvants on evaporation was preliminarily discovered-----The adjuvant forms a film structure at the interface between air and liquid to prevent water being evaporated.(2)Used Winner318 C laser granulometer to analyze the distribution characteristics of the fog droplets atomized by TR80-05 nozzle,researched the granule diameter evolution rule of water and the 3 types of adjuvants at different operation conditions and positions,set the medium diameter of the fog droplet volume that was after secondary atomization as the medium diameter of the stabilized volume,evaluated the respective influence of the 3 types of adjuvant on the outcome of atomization.The results show the adjuvant Maidao has the most significant capability in increasing the medium diameter of the fog droplets among the 3 types of adjuvant,due to its capability of increasing liquid viscosity and reducing surface tension.(3)Used MATLAB to develop the program for the single fog droplet movement evaporation,researched the influence rules of operation factors(droplet diameter,spray height)and environmental factors(temperature,relative humidity,horizontal wind speed)on the evaporation retention rate of fog droplets and the drift distance,used the orthogonal test to obtain the key factors that influence evaporation and drift respectively,and data was regressionfitted to generate the formula to quantitively calculate the evaporation retention rate and the drift distance.Combined with adjuvant factors and the distribution result of fog droplet diameters,calculated the amount of evaporation of the solutions with adjuvant under high,medium and low temperature conditions,and made recommendations for making adjuvant choices. |
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