Abstract This study investigated the heat transfer performance of three nanostructured surfaces and two plain surfaces: one roughened and one polished during the saturated pool boiling of refrigerants R-134a at 5 and 25 °C and R-245fa at 20 °C. Nanocoatings were applied to polished copper tubes through a layer-by-layer (LbL) process that deposited silica nanoparticles, a chemical oxidation process where an intertwined mat of sharp copper oxide (CuO) structures were generated and a commercial nanocoating process (nanoFLUX). A polished copper tube and a roughened copper tube were tested as comparison cases. All tubes were tested in the horizontal position in pool boiling over heat fluxes of 20 to 100 kW/m2, followed by a further increase in heat flux in an attempt to reach critical heat flux. The tubes were internally water heated and Wilson plots were conducted to characterise the internal heat transfer characteristics. The nanoFLUX surface had the highest heat transfer coefficients, the LbL and polished surfaces had the lowest heat transfer coefficients, and the CuO and roughened surfaces had intermediate heat transfer coefficients. The nanoFLUX surface had between 40 and 200% higher heat transfer coefficients than those of the polished tube. Both roughened tubes and nanocoated tubes showed typical exponentially increased heat transfer coefficients as heat flux was increased. However, the nanoFLUX and CuO surfaces displayed more heat flux sensitivity compared with the other surfaces. The nanoFLUX surfaces outperformed the other nanostructured surfaces due to a higher nucleation site density and outperformed the roughened tube due to a unique heat transfer mechanism. The nanoFLUX and CuO surfaces also experienced reduced critical heat flux compared with plain surfaces, thought to be caused by the trapping of vapour in the fibrous nanostructures, resulting in reduced wetting in the Cassie-Baxter state.

中文翻译：

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纳米结构和粗糙管上的制冷剂池沸腾

摘要 本研究调查了制冷剂 R-134a 在 5 和 25 °C 和 R-245fa 在 20 °C 的饱和池沸腾过程中三个纳米结构表面和两个平面的传热性能：一个粗糙表面和一个抛光表面。纳米涂层通过逐层 (LbL) 工艺沉积二氧化硅纳米粒子、化学氧化工艺（其中产生锐利的氧化铜 (CuO) 结构的交织垫）和商业纳米涂层工艺 (nanoFLUX) 应用于抛光铜管。将抛光铜管和粗糙铜管作为对比情况进行测试。所有管子都在水平位置以 20 到 100 kW/m2 的热通量在水池沸腾中进行测试，然后进一步增加热通量以试图达到临界热通量。管子被内部水加热，并进行威尔逊图来表征内部传热特性。nanoFLUX 表面的传热系数最高，LbL 和抛光表面的传热系数最低，CuO 和粗糙表面的传热系数中等。nanoFLUX 表面的传热系数比抛光管高 40% 到 200%。随着热通量的增加，粗糙管和纳米涂层管都显示出典型的传热系数呈指数增加。然而，与其他表面相比，nanoFLUX 和 CuO 表面显示出更高的热通量敏感性。由于更高的成核位点密度，nanoFLUX 表面优于其他纳米结构表面，并且由于独特的传热机制而优于粗糙管。与普通表面相比，nanoFLUX 和 CuO 表面也经历了降低的临界热通量，这被认为是由纤维纳米结构中的蒸汽捕获引起的，导致 Cassie-Baxter 状态下的润湿性降低。