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

表面形成纳米和微米级多孔层结构增强传热

基本信息

批准号：
16206022
负责人：
KUNUGI Tomoaki
金额：
$ 23.63万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

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.

本研究旨在探讨在平板表面形成纳米/微孔层结构的高换热机理。通过使用基础设备，我们确认通过多孔表面的净输入能量比没有任何多孔层的裸板增加了20-30%。我们考察了板厚对输入能量的影响，得到的结果都是一样的：板厚对传热增强没有影响。这意味着热阻在纳米/微孔层上占主导地位。然而，由于纳米/微孔层的厚度约为100微米，一般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很小，因此也可以忽略其作为流动搅拌器（即湍流促进器）的作用。另一方面，从SEM图像来看，该多孔层由许多颗粒组成，并且相互接触。这意味着这个多孔层可以看作是绝热介质。多孔层与金属板（即传热表面）之间的蚀刻层结合非常紧密，该层厚度最小在5~10 nm左右。这个厚度太薄，不能作为绝热层。因此，热流可以很容易地通过蚀刻层的薄部分。最终，热流会在那个薄的部分增加。由于热流的增加，多孔层内的水被加热，温度立即升高，最终达到壁温。这意味着这种充满水的纳米/微孔层结构可能起到类似流体壁的作用。这可能是表面形成纳米/微孔层结构增强传热的一种可能机制。