Use of environmentally safe refrigerants is the need of the hour to minimize the carbon footprints and to reduce the ozone depletion. The application of such environmentally safe refrigerants in the thermosyphon with the micro/nanoporous coating is expected to operate efficiently. In this study, a simple cost-effective anodizing technique to form a uniform thin micro/nanoporous coating at the inner wall of the thermosiphon is undertaken, and the resulting performance enhancement is presented. Also, the effect of fill ratio, heat input and the porous coating on the heat transfer characteristics of flat thermosiphon are studied. The heat transfer coefficient in the evaporator of anodized and nonanodized thermosiphon is enhanced to a maximum of 3587 and 2742 W/m2 K, respectively. The number of pores present in the anodized evaporator surface is estimated as 3.4 × 109. The width (pore size) and depth of pore are measured as 0.25 µm and 16 nm respectively. The porosity of the coating is around 55%, and the contact angle is ≤10°. As a result, the heat transfer coefficient at the evaporator and condenser of anodized thermosyphon is enhanced to a maximum of 24% and 13% respectively, when compared to that of the nonanodized thermosiphon.

中文翻译：

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阳极氧化平面热虹吸管的传热特性和流动可视化

使用对环境安全的制冷剂是减少碳足迹和减少臭氧消耗的迫切需要。这种环境安全的制冷剂在具有微/纳米涂层的热虹吸管中的应用有望有效运行。在这项研究中，采用了一种简单且经济高效的阳极氧化技术，可在热虹吸管内壁形成均匀的薄微/纳米多孔涂层，并展示了由此产生的性能增强。此外，还研究了填充比、热输入和多孔涂层对平面热虹吸管传热特性的影响。阳极氧化和非阳极氧化热虹吸管蒸发器的传热系数分别提高到 3587 和 2742 W/m2 K。阳极氧化蒸发器表面存在的孔数估计为 3.4 × 109。孔的宽度（孔径）和深度分别测量为 0.25 µm 和 16 nm。涂层孔隙率在55%左右，接触角≤10°。结果，与非阳极化热虹吸管相比，阳极化热虹吸管蒸发器和冷凝器的传热系数分别提高了 24% 和 13%。