| The freezing of water droplets is a common natural phenomenon.When water droplets hit or hang on the transmission wire in a low temperature environment,icing and adhesion will occur,resulting in icing of the transmission wire,which seriously affects people's production and the safe operation of the power grid.Therefore,it is necessary for us to conduct in-depth research on this phenomenon to clarify the icing mechanism in order to avoid this phenomenon.In this paper,the movement process of a droplet impacting a supercooled surface under an electric field is studied.The Phase Field method is used to track the phase interface,and the solidification phase change and ice growth of the droplet are described by the enthalpy-porosity method.At the same time,the electric field equation is coupled to combine the electric field force.The Kistler dynamic contact angle model is introduced into the study of the droplet impacting the surface.The main research contents are as follows:(1)Study the motion characteristics of droplets resting on a cold surface under the action of an electric field,establish a two-dimensional axisymmetric model of lying drop icing coupled by the Phase Field method and the enthalpy porous method,and analyze the changes in the flow field,electric field force and surface tension of the droplets.The stretching process of the droplet under the electric field and the solidification process under the supercooling condition,to study the influence of the hydrophobicity of the surface,the degree of supercooling,and the electric field strength on the droplet motion characteristics,the change of the charge density,and the change of the force.(2)Study the phase transition and motion characteristics of droplets impacting on low-temperature surfaces,and establish a two-dimensional axisymmetric model of droplet impact icing coupled with Phase Field method,enthalpy porous method and dynamic contact angle model,combining the morphological evolution of droplets,flow field and ice Layer change,analyze the movement and phase change process of droplets hitting the wall.The influence of surface hydrophilicity and hydrophobicity,surface temperature,droplet velocity and droplet diameter on the movement characteristics of droplets is studied.(3)Study the phase transition and motion characteristics of the droplet impacting the low-temperature surface under the electric field,and establish a two-dimensional axisymmetric model coupling the Phase Field method,the enthalpy porosity method,the dynamic contact angle model and the electric field model.Analyze the movement and heat transfer characteristics of the droplet through the morphological evolution of the droplet,the change of electric field and charge density,the evolution of the ice layer,and study the influence of parameters such as surface hydrophilicity and hydrophobicity,surface temperature,droplet velocity and electric field intensity.(4)The anti-icing performance of superhydrophobic surface induced coalescence droplet self-bouncing phenomenon is studied.In the simulation,a superhydrophobic surface with a wave structure is designed.The horizontal velocity and horizontal displacement of the droplet are used to study the structure to coalesce liquid.The influence of droplet movement is studied to analyze the ability of the superhydrophobic surface of the structure to remove droplets.The results show that the dynamic contact angle model considering the advancing and receding angle can better reflect the movement process of the droplet.For the icing process of a static droplet under an electric field,for hydrophilic surfaces,the field strength has little effect on the movement of the droplets,resulting in less electric field distortion and insignificant changes in the stretching height.For hydrophobic surfaces,increasing the field strength can significantly increase the stretching height of the droplet,and the wall temperature affects the freezing rate of the droplet.The lower the temperature,the greater the freezing rate.For the process of droplets impacting the supercooled surface,due to the high adhesion of the hydrophilic surface,the spreading length of the droplets does not change significantly.Besides,due to the surface adhesion of the superhydrophobic surface is small,the spreading length gradually decreases during the retraction process.The lower the wall temperature,the faster the growth rate of the ice layer,the more fully the spread and retraction of the droplet.When the droplet velocity increases,the more fully the droplet spreads and retracts,the easier it is to produce satellite droplets.The smaller the droplet diameter,the shorter the duration of the droplet's spreading and retraction process,and the less likely it is to produce satellite droplets.For the process of droplets hitting the supercooled surface under the electric field,the intensity of the electric field and the speed of the droplets have a greater influence on the electric field force that the droplets receive,while the temperature has less.The electric field strength determines the initial electric field force of the droplet,and the subsequent tensile deformation of the droplet is related to the local field strength distortion,meanwhile,The field strength distortion caused by droplets on superhydrophobic surfaces is significantly greater than that on hydrophilic surfaces.The greater the field strength distortion,the greater the electric field force and charge density,and the stronger the droplet stretching ability.The stretching continues to increase the field strength distortion and electric field force,and the droplet is continuously stretched under the reciprocating cycle.In terms of surface design with anti-icing function,it is found that the horizontal velocity and horizontal displacement of the coalesced droplets on the superhydrophobic surface with wave structure are increased by 1600% compared with the flat wall surface,which is beneficial to realize the removal of a considerable amount of droplet along the path of the sweeping wave surface.The research in this article can provide a certain reference for the research of transmission line icing mechanism and transmission line anti-icing technology. |
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