Research On Spreading And Migration Characteristics Of Droplet Impact On A Hydrophobic-Hydrophilic Surface

Propellant management is significant in the propellant transportation in orbit.This work is based on the background of the propellant management in orbit refueling tank aiming to the possible resolution for the application in practice and the extended application in the near future.The thesis employs both the analytic and experiment methods to study the basic flow theory with capillarity.Focus on the flow problem during the process of large flow and the track transfer between different orbits.The propellant management enhancement technology is promoted based on the wettability regulation.Analytic and experimental research has been conducted on droplet spreading and migration dynamics.Some theoretical and practical results have been derived and can supply some advisement on the propellant management.The main contents of the thesis are:(1)Theoretical and experimental research on the wettability of microstructure surface.Based on the traditional wetting theory the wettability regulation is remodeled on microstructure surface.Experiments on the wettability regulation effect has been confirmed.Theoretical and experimental results show value on the instruction of the traditional wetting theory and the practical manufacture about the detailed microstructure size and patterns.(2)Theoretical research on flow dynamics along the capillary tubes with microstructure surface.Based on capillary flow dynamics which is the physical fundamental of the surface tension tank,the capillary flow in tubes with microstructure surface inside are theoretically analyzed.The effect of different microstructure units and gradient are analyzed theoretically.(3)Theoretical and experimental research on droplet impact state and dynamics on smooth solid surface.Based on the jet phenomena due to the large flow velocity during propellant transportation,the theoretical model of impact state and dynamics are built on the droplet impact on smooth solid surface.Using the mass conservation and energy conservation,the critical rebound factor is analyzed under relatively high impact velocity.Spreading dynamics during droplet impact is also researched and relations between spreading diameter versus time and the maximum spreading diameter versus initial factors are derived.These relations can be a base for propellant self-management.(4)Theoretical research on droplet impact dynamics on wettability gradient solid surface.Dynamics during the solid surface with wettability gradient is analyzed.The common laws on spreading dynamics on radial wettability gradient and the migration dynamics only along x-axis is derived.Inducing the Doi-Onsager principle,the migration dynamics along x-axis is remodeled and solved concisely.The theoretical results of Doi-Onsager principle about droplet migration dynamics are comparable with others' work.This provides a theoretical instruction on wettability design for droplet migration.(5)Theoretical and experimental research on wedge-patterned biphilic surface.Wedge-patterned biphilic surface is fabricated with the philic wedge pattern and the other areas where is superhydrophobic by chemical coating.Spreading dynamics on wedge-patterned biphilic surface is built.Relations of spreading diameter versus time and maximum spreading diameter versus different initial impact states are given.The effect of apex angles and impact velocities on droplet spreading dynamics are analyzed.These contents provide a reference for droplet spontaneous migration.(6)Theoretical and experimental research of droplet migration dynamics on wedge-patterned biphilic surface.The migration dynamics of droplet impact on wettability gradient surface has been built.Effect of apex angle,impact velocity and the velocity direction on spreading dynamics are well researched and confirmed by experiments.It can be a base to design a better management for propellant transportation with the application of biphilic surface.Droplet impact on solid surface has been further researched with the background of propellant transportation during refueling in orbit.Some common laws on droplet spreading and migration dynamics are achieved and an extension research of fluid flow within a restricted region has been explored.This work can be used in improving the management efficient as well as the jet problem.It shed the light for the possible way to self-management in propellant management during transportation.