Development of Practical TiO_2 Heat Transfer Surface by Advanced Coating Technique

二氧化钛作为光催化剂之一，由于其在紫外光的辅助下对有害物质具有很强的氧化能力而备受关注。在本研究计画中，我们尝试利用火焰喷涂技术来开发一种实用的二氧化钛热传表面。实验结果表明：（1）在池沸腾过程中，亲水表面的传热系数和临界热流密度均大于正常表面;（2）在降膜蒸发过程中，亲水表面的传热系数和临界热流密度均大于正常表面。表面形成稳定的薄水膜，最大换热系数可提高40倍在浸入式冷却中，具有亲水涂层的铁水比正常表面冷却得更快。在水滴蒸发实验中，水滴在超亲水表面上的寿命比在正常表面上的寿命短得多，尤其是在低温区。对火焰喷涂表面进行了池沸腾实验研究。为了比较，还测试了使用溅射和镜面的实验，并得到以下结果：a）火焰涂层的临界热通量与正常表面相比增加了1.5倍。B）在较高热流密度区，涂层厚度对降膜蒸发的传热特性影响较大，本文还进行了火焰喷涂、溅射和镜面降膜蒸发实验，发现在较低温度区，火焰喷涂表面的传热效果最好; B）在较高温度区，火焰喷涂表面的传热效果最好;涂层的厚度和结构对传热特性有影响。

Titanium dioxide, one of photocatalysts, has been in spotlight since it has a strong oxidation power to harmful substances with the aid of UV light. In this research project, we tried to develop a practical TiO2 heat transfer surface by making use of flame coating technique. The four kinds of experiments have been performed and the results are summarized as follows.1) In pool boiling, heat transfer coefficient and critical heat flux for hydrophilic surface become larger than those for normal surface.2) In falling film evaporation, thin stable water film can be realized on the surface and resultant heat transfer coefficient increased by 40 times as the normal surface at its maximum case.3) In immersion cooling, hot metal with hydrophilic coating is cooled down more rapidly than normal surface. The time required to cool down is tremendously shorten.4) In water drop evaporation experiment, life time of water drop on superhydrophilic surface becomes much shorter than that on normal surface especially in lower temperature region. The wetting limit temperature increased for superhydrophilic surface.Pool boiling experiment using flame coating surface was conducted. For comparison, experiments using sputtered and mirror surfaces were also tested and the following results were obtained.a) Critical heat flux for flame coating increased by 1.5 times compared with the normal surface. However, heat transfer coefficient at higher heat flux decreased.b) In higher heat flux region, heat transfer characteristic is much influenced by the thickness of coating layer.We also conducted experiment of falling film evaporation using flame coating, sputtering and mirror surfaces and found the followings.a) In lower temperature region, flame coating surface is the best among three surfaces.b) In higher temperature region, thickness of coating layer and its structure influence the heat transfer characteristics.