纳米仿生皮肤传热传质特性研究

发布时间：2018-05-01 13:13

本文选题：纳米仿生皮肤 + 发汗冷却　；参考：《武汉大学》2014年博士论文

【摘要】：移动通讯设备的迅速发展,使得高性能手机有可能代替计算机成为下一代通用移动电子设备,然而其实现仍有一道技术瓶颈,那就是散热。本文在传统散热技术基础上,结合最新纳米技术的发展,提出了一种新的用于手机表面温度控制的发汗冷却(Transpiration Cooling)技术—纳米仿生皮肤。其基本思路是模仿生物体体温调节的机理,当设备发热较多或者设备所处环境温度较高时,从纳米多孔表面(即“皮肤”)释放出水分(即“汗”),利用水分的蒸发相变和质传递带走大量的热量。蒸发(即“发汗”)过程中散失的水分,可以在电子设备充电的时候,从空气中冷凝在微纳米结构壁面上,继而输运到贮水介质纳米级温度敏感型水凝胶中。基于该项技术,本文重点研究冷凝取水过程中微纳米拓扑结构对取水效率的影响以寻找高效的冷凝壁面,以及发汗冷却过程中纳米多孔介质内的蒸发问题,最后对整个纳米仿生皮肤进行测试。本文具体的研究内容和结论包括： (1)纳米仿生皮肤冷凝取水,其本质上为含不凝结气体的蒸汽冷凝问题。本部分提出了两种可以直接在金属铜基底上合成的微纳米拓扑结构-润湿性梯度结构和微纳米二级穹顶结构,冷凝实验结果表明前者冷凝效率为光滑铜表面的1.3倍,而后者表面上可以形成持续稳定的珠状凝结,其冷凝效率可以达到光滑铜表面的1.8倍和普通疏水表面的2倍。通过对冷凝壁面上的液滴行为进一步的理论分析和数值模拟,证明了微纳米拓扑结构可以明显影响冷凝液滴的生长、融合和扫落过程,进而影响含不凝结气体的蒸汽冷凝效率。 (2)纳米仿生皮肤发汗冷却,其本质上为纳米多孔介质内水分蒸发问题。通过光学实验方法研究了纳米仿生皮肤释水及蒸发性能,证明了其发汗冷却功能的可行性；为了进一步强化纳米仿生皮肤的发汗冷却性能,本部分提出了两种可以明显强化液体蒸发的纳米多孔结构—亲水及疏水的规则纳米通道,在相对湿度RH=91%时,两者单位面积水分蒸发速率可以分别达到宏观水面的30倍和40倍；同时,发现纳米颗粒堆积体系可以降低液体的蒸发速率。在整个过程中分析讨论了纳米结构内液体的蒸发机理,并得出了通过改变纳米结构,被动的控制液体蒸发速率的方法。 (3)纳米仿生皮肤性能测试。建立了一套高效稳定的纳米仿生皮肤凝水和发汗冷却系统并进行了不同环境情形下的测试。结果表明该冷凝系统在30%-100%相对湿度范围内均能满足高性能电子设备的冷却需水量(10g)；在不同温度和环境相对湿度下,纳米仿生皮肤发汗冷却的换热系数均可达到自然冷却(包括自然对流和辐射)的两倍以上。本文不仅提出了一种可行的无风扇高性能手机散热技术,而且对其内部的基础的气液相变问题进行了研究。这些不仅能为新型的电子设备散热技术提供指导,而且可以为纳米结构内的传热传质提供新的启示。
[Abstract]:The rapid development of mobile communication equipment makes it possible for high-performance mobile phones to replace computers to become the next generation of general mobile electronic devices. However, there is still a technical bottleneck, which is heat dissipation. Based on the traditional heat dissipation technology, this paper puts forward a new kind of temperature control for mobile phone surface combined with the development of the latest nanotechnology. Transpiration Cooling technology - Nano biomimetic skin. Its basic idea is to imitate the mechanism of body temperature regulation. When the equipment has more heat or the temperature of the equipment is high, the water ("sweat") is released from the porous surface (that is "skin"), and the evaporation phase change and mass transfer of water are taken away by the mass. The loss of moisture in the process of evaporation ("sweating") can be condensed from the air to the micro nanostructure wall and then transported to the nanoscale temperature sensitive hydrogel in the water storage medium when the electronic equipment is charged. Based on this technique, the paper focuses on the micro and nano topology of the condensing process for water intake. The effect of the rate is to find the efficient condensing wall, and the evaporation problem in the porous media during the perspiration cooling process. Finally, the whole nano biomimetic skin is tested.
The specific contents and conclusions of this paper include:
(1) the condensation of nano biomimetic skin is in essence the condensation of steam containing non condensable gases. In this part, two kinds of nano topologies, wettability gradient structure and micro nano dome structure, which can be synthesized directly on the metal copper substrate, are proposed in this part. The condensation experiment results show that the condensation efficiency of the former is 1.3 times of the smooth copper surface. The latter can form a steady and stable bead like condensation, and the condensation efficiency can reach 1.8 times the surface of the smooth copper and 2 times that of the ordinary hydrophobic surface. By further theoretical analysis and numerical simulation of the droplet behavior on the condensing wall, it is proved that the micro and nano topology can affect the growth, fusion and sweep of the condensate drops obviously. The falling process affects the steam condensing efficiency of non condensable gas.
(2) the nano bionic skin is perspiration cooling, which is essentially water evaporation in nanoscale porous media. Through the optical experimental method, the water release and evaporation properties of nano biomimetic skin are studied, and the feasibility of its perspiration cooling function is proved. In order to further strengthen the perspiration cooling performance of nano biomimetic skin, two kinds of methods are proposed. The nano porous structure, hydrophilic and hydrophobic, is obviously enhanced by the liquid evaporation. At relative humidity of RH=91%, the evaporation rate per unit area of water can reach 30 times and 40 times as much as the macro water surface. Meanwhile, it is found that the deposition rate of the nanoparticles can be reduced. The evaporation mechanism of the liquid in the nanostructure is obtained, and the method of passive control of liquid evaporation rate is obtained by changing the nanostructure.
(3) nano biomimetic skin performance test. A set of efficient and stable nano biomimetic skin condensate and transpiration cooling system were established and tested in different environmental conditions. The results showed that the condensing system could meet the cold water requirement (10g) of high performance electronic equipment in the relative humidity range of 30%-100%; at different temperatures and environment phases. Under humidity, the heat transfer coefficient of nano bionic skin transpiration cooling can be more than two times that of natural cooling (including natural convection and radiation).
This paper not only puts forward a feasible heat dissipation technology for the high performance mobile phone with no fan, but also studies the problem of gas-liquid phase transformation in its inner base, which can not only provide guidance for the new electronic equipment heat transfer technology, but also provide new inspiration for the heat and mass transfer in the nanostructure.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TB383.1;R318.1

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