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

本研究旨在探讨在平板表面形成纳/微米多孔层结构强化传热的机理。我们证实，通过这种多孔表面的输入能量的净量是20-30%的增加相比，裸板没有任何多孔层，通过使用的基本设备。我们研究了板厚度对输入能量的影响，然后得到的结果表明：板厚度对传热增强没有影响。这意味着热阻在纳米/微孔层处占主导地位。然而，由于纳米/微米多孔层的厚度为约100微米，因此通常可以忽略其作为热阻。此外，由于该厚度与层流边界层厚度相比也可以如此小，因此其也可以忽略为流动搅拌器（即，湍流促进器）。另一方面，从SEM图像来看，该多孔层由许多颗粒组成并且彼此接触。这意味着该多孔层可以被认为是绝热介质。此外，多孔层和金属板之间的蚀刻层（即，传热表面）显示出非常紧密的结合，并且该层厚度约为最小5~10 nm。该厚度太薄而不能用作绝热层。因此，热流可以容易地通过蚀刻层的该薄部分。最终，热流会在薄的部分增加。多孔层内的水可以通过这种增加的热流加热，并且温度立即升高并最终达到壁温。这意味着这种填充有水的纳米/微孔层结构可以充当流体状壁。这可能是通过在表面上形成的纳米/微米多孔层结构的这种传热增强的可能机制。

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.