Deposition Mechanism On A Pesticide Droplet Impacting Onto Tea Leaves Based On Interface Tracking Method

Tea is known as "National Drink" in China.However,the export volume of tea in China has declined year by year since 2012.The main reason is that the pesticide residue of tea is seriously exceeded the standard,which does not conform to the international quality standard of animal and plant hygiene.Thus,it is of great practical significance to study the scientific methods for the effective control of pesticide use in the process of tea growth.In this paper,based on Shucha Zao,the CFD numerical simulation method of computational fluid dynamics is used to establish the model and mesh division in Gambit.Then the composite Level Set-CLSVOF method of gas-liquid two-phase flow interface tracing and the continuous surface tension model were used in ANSYS Fluent14.0.The deposition,rebound and sputtering of a single pesticide droplet on the leaf surface of Shucha-Zao were numerically simulated from the horizontal and longitudinal directions respectively.Analysis the distribution of liquid phase,wettability of the surface,pressure,spreading velocity to study the effects of the physicochemical properties of three commonly used pesticide droplets(such as Chlorothalonil,dimethoate and Malathion)on the kinetic behavior of impacting Tea Surface.On this basis,because the contact angle between the droplet and the tea leaf surface is dynamic during the process of the pesticide droplet impact on the tea leaf surface,the User-Defined Function is used to import the dynamic contact angle program.After comparing and analyzing the four key factors of the deposition mechanism of tea leaves by pesticide droplets,the contact angle changes of each step were measured and analyzed,and the relationship between the contact angle change and the spreading process was obtained.The numerical analysis of the whole process of pesticide droplets impacting tea leaves was perfected.The waxy surface of tea leaves was also considered in this paper.The waxy layer was added to the numerical model and the dynamic contact angle model was used to simulate the impact of pesticide droplets on the waxy surface of Shucha early leaves.The changes of liquid phase distribution,surface wetness,pressure distribution,velocity distribution and dynamic contact angle under the same working conditions were compared and analyzed.It was concluded that the wax of tea leaves spread and split during the movement of the pesticide droplets after the impact of the wax on the tea leaves.The effect of various stages,such as retraction.Through the research in this paper,the internal mechanism and changing law of pesticide droplet impingement deposition process can be understood,which can deepen the understanding of nature and science and technology,increase the adhesion rate of pesticide droplet on tea leaves,and reduce the rolling or sputtering of pesticide droplet.The stable deposition on the leaf surface can improve the biological control efficiency of pesticides and provide an important theoretical basis for improving and improving the efficiency of pesticide application.