Study On Structure Control And Photo-thermal Conversion Property Of Black TiO₂ Nanotubes On Ti Tube Surfaces

Photo-thermal conversion is a process that collects and converts solar radiation energy into thermal energy.It assists with conversion processes such as photoelectric and photochemical to meet the diverse needs of energy loads;among them,solar collector tubes are currently one of the most mature application methods.However,the heat collection tube is usually based on transparent glass material,which has major problems such as poor thermal conductivity,high brittleness,and difficulty in coating control.At the same time,in the face of the development needs of miniaturization,integration and portability of heat collection components,it is urgent to develop new heat collection materials and devices with good thermal conductivity,low density,easy processing and easy integration.Therefore,this project proposes to use low-density metal titanium tube as the substrate,by adjusting the structural characteristics of the nanotube coating on the inner and outer surface of the titanium tube,expanding the absorption spectrum and improving the thermal conductivity,designing and implementing a new metal tube-based heat collection tube technology,It solves the problems of poor thermal conductivity,brittleness,and difficulty of coating control of traditional glass materials,laying a theoretical and experimental foundation for the development of new heat collector tubes.This project adopts the coaxial electrochemical anodic oxidation method to grow and regulate the TiO₂ nanotube coating in situ on the inner and outer surface of the metal titanium tube,and explore its influence on the light-to-heat conversion performance.The main research results obtained in this paper are as follows:The growth characteristics of TiO₂ nanotubes on the outer surface of titanium tubes and their effects on the photo-thermal conversion performance were studied.The black TiO₂ nanotube array on the outer surface of the titanium tube has a high oxygen vacancy concentration,which reduces the width of the band gap and increases the absorption of low-energy photons,thereby significantly improving the photo-thermal conversion performance of the film.When the thickness of the TiO₂ nanotube film is less than 2?m,as the thickness of the nanotube array increases,the working temperature of the collector tube gradually rises;when the thickness of the TiO₂ nanotube film is greater than 2?m,as the thickness of the nanotube array increases,the working temperature of the heat pipe decreases gradually.Therefore,the best photo-thermal conversion effect can be obtained by preparing the appropriate thickness of the nanotube arrays.The influence of the wettability of the TiO₂ nanotubes on the inner surface of the titanium tube and the thickness of the coating on the performance of the collector tube was studied.When the inner surface of the titanium tube is super-hydrophilic,the stable working temperature reaches 72°C;when the inner surface is super-hydrophobic,the stable working temperature reaches 64°C;and the stable working temperature of the titanium tube without treatment on the inner surface is 70°C.Therefore,the preparation of a super-hydrophilic coating on the inner surface of the titanium tube can improve the heat transfer performance,while the super-hydrophobic coating will reduce the heat transfer performance.This project systematically studied the influence of TiO₂ nanotubes on the inner and outer surfaces of titanium tubes on the performance of photo-thermal conversion,and analyzed and discussed the influence mechanism.The experimental results show that the black TiO₂ nanotube array of about 2?m is prepared on the outer surface of the titanium tube by the coaxial electrochemical anodization method,and the super-hydrophilic nanotube coating is prepared on the inner surface,and the photo-thermal conversion efficiency can reach about 85%.