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.

这项研究是为了研究板表面上形成的纳米/微型多孔层结构的高热传递增强的机制。我们证实，与裸板相比，通过使用基本设备而没有多孔层的净输入能量增加了20-30％。我们检查了板厚度对输入能的效应，然后获得了结果，结果显示了所有相同的内容：板厚度对热传递增强没有影响。这意味着热电阻在纳米/微孔层上是主要的。但是，由于纳米/微孔层的厚度约为100微米米，因此通常可以忽略作为热电阻。此外，由于与层流边界层厚度相比，这种厚度也可能很小，因此它也可以忽略为流动搅拌器（即湍流启动子）。另一方面，从SEM图像中，该多孔层由许多粒子组成，并相互接触。这意味着该多孔层可以被视为绝热培养基。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。这种厚度太薄而无法充当绝热层。因此，热流很容易通过蚀刻层的薄部分。最终，热流可以在薄的部分增加。多孔层内的水可能会因这种增加的热流而加热，并且温度立即升高并最终达到壁温度。这意味着用水充满的纳米/微量多孔层结构可能充当流体状壁。这可能是通过在表面上形成的纳米/微型多孔层结构来增加这种传热的可能机制。