Superhydrophobic Coating And Its Drag Reduction Performance

In recent years,superhydrophobic surface shows wide application prospects in many fields such as industrial production and daily life due to its excellent performance.For example,it can be applied to automotive glass and glass facades due to its self-cleaning performance and effectively prevent transmission lines from ice and snow.In addition,the excellent drag reduction characteristics of superhydrophobic surface provide a new idea for fluid drag reduction,which is widely concerned by researchers at home and abroad.Reducing fluid resistance can improve energy utilization,reduce the energy consumption of equipment,and help build an environment friendly and energy-saving society.This is of great significance for fluid machinery,pipeline transportation,ship transportation and so on.In this study,a fluid resistance measurement device is designed and built,and drag reduction performance of superhydrophobic surface is characterized through the flow pressure difference experiment.The research contents of this paper can be summarized as follows:(1)A fluid resistance measurement device on purpose of the characterization of drag reduction performance is designed and constructed based on flow pressure difference experiment.First of all we designed the outline of the device,and then the sections such as the pressure measurement section,the selection of the differential pressure meter,the selection of the flowmeter,the selection of the water pump,the determination of the size of the tank and so on.In addition,in order to improve the accuracy and applicability of the device,seal design,tail lifting and water outlet valve design were carried out.A fluid resistance measuring device with wide measuring range and changeable pressure section is constructed.(2)The drag reduction performance of EP/FEP/m-ZnO superhydrophobic surfaces is characterized.When the Reynolds number is 500~1500,the drag reduction rate of the surface is 32.6%,and when the Reynolds number is 1500~2000,the drag reduction effect of the EP/FEP/m-ZnO superhydrophobic surface varies with the Reynolds number,the minimum drag reduction rate is 25.2%,the maximum drag reduction rate is 66.8%,and the average drag reduction rate is 49.1%.The comparison with the ordinary channel shows that the EP/FEP/m-ZnO superhydrophobic surface can increase the transition Reynolds number of the flow in the channel,and the effect of the drag reduction can be achieved by "delaying" the transition of the turbulent flow.The change of drag reduction performance of EP/FEP/m-ZnO superhydrophobic surface with different chemical composition shows that the existence of low surface energy and the construction of micro nano composite rough structure are twomain factors affecting the drag reduction performance of EP/FEP/m-ZnO superhydrophobic surface.(3)The drag reduction performance of PVDF/FEP/CNFs superhydrophobic surfaces is characterized.When the Reynolds number is 500~1500,the drag reduction rate of the surface is 27.2%,and when the Reynolds number is 1500~2000,the drag reduction effect of the PVDF/FEP/CNFs superhydrophobic surface varies with the Reynolds number,the minimum drag reduction rate is 23.9%,the maximum drag reduction rate is 64%,and the average drag reduction rate is 46.8%.The comparison with the ordinary channel shows that the PVDF/FEP/CNFs superhydrophobic surface can also increase the transition Reynolds number of the flow in the channel,and the effect of the drag reduction is achieved by "delaying" the transition of the turbulent flow.The change of drag reduction performance of PVDF/FEP/CNFs superhydrophobic surface with different chemical composition shows that the existence of low surface energy and the construction of micro nano composite rough structure are two main factors affecting the drag reduction performance of PVDF/FEP/CNFs superhydrophobic surface.(4)The possible reasons why the contact angle and rolling angle of the superhydrophobic surface is irrelevant to the drag reduction performance of the superhydrophobic surface and the reasons for the differences between the superhydrophobic surface of EP/FEP/m-ZnO surface and the superhydrophobic surface of PVDF/FEP/CNFs are analyzed.