چكيده به لاتين
Condensation is one of the most important processes in thermal management engineering. Condensation forms on surfaces in filmwise or dropwise regime. Research has shown that heat transfer rate in the dropwise condensation is ten times higher than that of the filmwise. Therefore many investigations have been carried out to develop stable methods for fabricating surface with dropwise condensation. Considering the direct relation between the surface and condensation and their impact on each other, heat transfer enhancement can be expected to be achieved by improving the surface quality.
Existence of micro/nano scale surface roughness and low surface energy are two main components of superhydrophobic surfaces. Generating superhydrophobic property on stainless steel, aluminum and copper has been investigated experimentally in this study. Due to the high surface energy of metals, generating superhydrophobic property on these surfaces requires reduction of their surface energy in addition to creating micro/nano scale on their surfaces. Chemical etching process which uses HCl acid was used to produce superhydrophobic aluminium and sainless steel and create surface roughness. Moreover two processes have been employed to generate superhydrophobic property on copper surface. In the first method, chemical etching process has been used using FeCl (III) to create micro/nano structure. Also, to reduce surface energy and enhance superhydrophobicity, stearic acid has been used on the surface by deposition process. In the second method, to create roughness, oxidation and to reduce surface energy, 1-octadecyl mercaptane was used. While investigating the effects of various parameters such as concentration of etch solution, concentration of energy surface reducer solution and immersion time of copper samples in these solutions, optimum value for each parameter was obtained.
Superhydrophobic property on surface is measured by static and sliding contact angles of a water droplet placed on the surface. Static and sliding contact angles of the superhydrophobic copper sample fabricated by the first method are measured to be higher than 153 degrees and less than 8 degrees respectively. Moreover the static and sliding angle contact angles of the superhydrophobic copper sample fabricated by the second method are measured to be higher than 162 degrees and less than 2 degrees respectively. Finally, to investigate the effect of superhydrophobicity property on heat transfer augmentation, superhydrophobic copper sample (fabricated by the second method) is tested in condensation setup.
Keywords: Condensation, superhydrophobicity, micro-nano structure, surface energy.
