Research On Directional Transport Characteristics Of Droplets In A Bionic Wetting Structure

The phenomenon of directional transportation of droplet is widespread in nature.For example,the back surface of the Namib desert beetle can realize the collection and directional transportation of droplets.As a method of imitating the functions and behaviors of biological systems,bionic technology has been widely used in scientific research in recent years.Therefore,the research on the directional transport of droplet based on the bionic method is of great significance to many fields such as micro-nano electromechanical systems,energy and chemical engineering.However,as the flow of liquid droplet involves a complex three-phase interaction of solid,liquid and gas,the droplet transport results will be affected by the physical parameters and size of the droplets,and the structure and wetting characteristics of the solid phase substrate.Based on the above reasons,this thesis takes the droplet as the research object to carry out the research on the directional transport characteristics of the droplet in the bionic functional wetting structure.Combined with the P-R non-ideal gas state equation,a multi-relaxation Shan-Chen pseudo-potential model is constructed based on the Lattice Boltzmann method.The established model is used to simulate the gas-liquid two-phase separation,and the separation density of the gas-liquid two-phase equilibrium is obtained.Using the obtained gas-liquid separation densities,the contact angles of droplet on different solid surfaces are simulated and the Laplacian pressure difference of droplet without solid is calculated.The result shows that the relationship between the force coefficient?_w and the contact angle of the droplet is almost linear,and the contact angle can be changed by choosing different values of?_w.The accuracy of the surface tension between three phases is verified.In addition,the pressure difference inside and outside the droplet is consistent with Laplace's law,and the pressure difference at the interface changes linearly with1/r.The calculated surface tension?between fluid and fluid is 0.082,and the accuracy of the established model is finally verified.The established model is used to simulate the directional transport process of droplets on the surface of a functionally wetting flat plate.The effect of wettability and droplet viscosity changes on its flow behavior is analyzed,and the relationship between wettability and viscosity ratio is discussed.The competition mechanism in the process of droplet transportation and the force in the process of droplet transportation are analyzed.The research results show that the contact angle on the right side of the droplet is always smaller than that on the left side,which makes the droplet force unbalanced and provides a driving force for droplet.Also,the larger the wetting span of the wall and the smaller the viscosity is,the faster the droplet transport is.As well,the wettability and the droplet viscosity will change the vertical force of the droplet,and ultimately affect the transport speed and spreading morphology of the droplet.The established model is applied to simulate the transport process of droplet in heterogeneous wettability porous media.The influence of porous media pore structure and wettability on the transport process of droplet are discussed,and the forces on the droplet are analyzed.The research result shows that in heterogeneous wettable porous media,droplet can only penetrate from the superhydrophobic side to the superhydrophilic side,but cannot penetrate from the superhydrophilic side to the superhydrophobic side.This phenomenon is caused by the combined action of gravity,hydrophilic and hydrophobic forces,and capillary forces on the droplet.An experimental platform for the directional transport of droplet is built,and the experimental research on the directional transport of droplets is carried out by changing the geometrical construction and wettability of copper-based materials,Also,the adaptability of the prepared surface in the high-temperature and high-humidity working environment was analyzed.The research result shows that the wettability modification of copper-based materials is achieved,and the range can be changed from super-hydrophilic to super-hydrophobic.The wettability of the prepared surface cannot be affected by the high-temperature and high-humidity working environment.In addition,the method of adding a lubricating oil layer on the surface can effectively solve the problem of contact line pinning,eliminate the hysteresis force in the droplet transportation process,and finally realize the directional transportation of the droplet,which is also verified by simulation.