Effect of Temperature on the Surface Characteristics of Anodized Aluminium Tubes

摘要

Thin porous coating was found to be vital for boiling heat transfer enhancement in various heat transfer devices that use a phase change mechanism. However, the formation of a stable thin porous surface is a challenging process. It is known that the aluminium tubes were used to fabricate different kinds of heat pipes which are used in space applications. Therefore, developing nanoporous coating in an aluminium tube is essential to improve the performance of heat pipes. Anodization is an electrochemical process that applied mostly for aluminium materials to protect the surface from corrosion. This anodized aluminium surface can also be utilized for heat transfer applications by controlling the morphology of the surface through adjusting the process parameters of the anodization. One of the most critical parameter that controls the morphology of coating surface is the temperature of the anodizing cell. Therefore, in this study, the effect of cell temperature on the coating thickness, pore size and contact angle is analysed while maintaining the electrolyte concentration, cell voltage, electrolyte flow rate and anodizing time as constant. An aluminium tube of the outer and inner diameter of 19 mm and 16.8 mm, respectively, with a length of 350 mm was used for anodization. The anodized aluminium tubes were characterized by analysing the surface morphology, coating thickness, pore size and contact angle. It was found that the formation of micro/nanoporous structure in the inner layer of aluminium tube with the pore size ranging from 2.05 μm to 3.6 μm and contact angle less than 10° between the temperature range of 20-35°C when 10% H_2SO_4 solution is used as the electrolyte.