Basic Research on the Heat Transfer Augmentation with High Performance by the Micro-Scale Concave-Convex Surfaces

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As a basic research to realize the heat transfer augmentation with high performance by using the heat transfer surface with nano-meter to micron-scale concave-convex structure, present research is aimed at pursuing the possibility of drag reduction and heat transfer augmentation in these surfaces, and making clear the mechanism. At first, experiments were conducted on the drag reduction. The drag reduction was observed by maximally 10 % with the ultra small scale concave-convex surface, and further the drag reduction by almost 5% was confirmed with smooth water-repellent surface with hydrophobic coating. As a second step research, experiments on the forced convection heat transfer with ultra small scale surfaces were conducted. The temperature distributions by several ゜C higher than the predictions assuming smooth surface were derived and it was estimated that there was the thermal resistance on the surface. The existence of the air layer at the solid-liquid interface where the surface energy is low was estimated as the reason. As a theoretical research on the drug reduction on the surfaces with ultra small scale concave-convex and hydrophobic coating, molecular dynamics simulation has been conducted based upon a hypothesis that boundary slip can occur if solid-liquid intraction is weakened. The analysis is to study the boundary slip in Couette flow of Lennard-Jones fluid confined by two walls apart by about 20 times of molecular diameter. The results shows the ship when Lennard-Jones parameter for energy depth are given by a factor of 0.1 or 0.5 compared with the parameter for liquid-liquid interaction. As shown above, the new results on the heat transfer augmentation on the surfaces with ultra small scale surfaces have been derived experimentally and theoretically.