Heat transfer augmentation with nano-and micro-scale porous layer structure formed on the surface

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This study is to investigate the mechanism of high heat transfer augmentation with nano/micro porous layer structure formed on the plate surface. We confirmed that the net amount of input energy through this porous surface was 20-30% increase compared to the bare plate without any porous layer by using the fundamental equipment. We examined the plate thickness effect on the input energy and then obtained the results showed all the same: no effect of the plate thickness on the heat transfer augmentation. This means that the thermal resistance is predominant at the nano/micro-porous layer. However, since the thickness of the nano/micro-porous layer is about 100 micron meter, in general it can neglect as a thermal resistance. Moreover, since this thickness can also be so small compared to the laminar boundary layer thickness, it can also neglect as a flow agitator (i.e., turbulence promoter). On the other hand, from the SEM image, this porous layer consisted of many particles and contacted with each other. This means that this porous layer can be considered as an adiabatic medium. Moreover, the etching layer between porous layer and the metal plate (i.e., heat transfer surface) shows very tight binding and this layer thickness is around minimum 5~10 nm. This thickness is too thin to act as an adiabatic layer. Therefore, the heat flow can easily pass through this thin part of the etching layer. Eventually, the heat flow can increase at that thin part. The water inside the porous layer could heat up by this increased heat flow and the temperature immediately increases and finally reaches to the wall temperature. This means that this nano/micro porous layer structure filling with water might act as a fluid-like wall. This might be a possible mechanism of this heat transfer augmentation by the nano/micro porous layer structure formed on the surface.