Abstract Dropwise condensation heat transfer (DWC) on superhydrophobic nanograsses surface (NGS) was investigated for long-term operation. For DWC of pure water-vapor on fresh NGS, two heat transfer regimes are identified: higher heat transfer coefficients with droplet jumping, and constant heat transfer coefficients with droplet rolling. The one-week operation not only deteriorates heat transfer performance, but also changes jumping or rolling mode to sliding mode. The condensation heat transfer coefficients are apparently decreased from first to third day, but they approach a limit value since the third day. In order to identify if the single-molecule-layer of polymer (SML) modified on nanograsses was destroyed, DWC on a smooth single-molecule-layer of polymer surface (SSML) was tested to display stable heat transfer with drop sliding for one-week operation, concluding no failure of the polymer layer. The collapse and breakage of nanograsses were observed to explain the decayed heat transfer versus time on NGS. Compared with SSML, the NGS has smaller droplet departure size but lower heat transfer coefficients, indicating positive and negative effects after introducing nanostructures. Three nanostructure failure mechanisms are proposed. This work suggests a new research field of the nanoscale fluid-wall interaction.

中文翻译：

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超疏水纳米结构表面上的滴状冷凝，第一部分：长期运行和纳米结构失效

摘要 研究了超疏水纳米草表面 (NGS) 上的滴状冷凝传热 (DWC) 以实现长期运行。对于新鲜 NGS 上纯水蒸气的 DWC，确定了两种传热方式：液滴跳跃时的较高传热系数和液滴滚动时的恒定传热系数。一周的运行不仅使传热性能变差，而且将跳跃或滚动模式变为滑动模式。冷凝传热系数从第一天到第三天明显下降，但从第三天开始接近极限值。为了确定纳米草上改性的聚合物单分子层（SML）是否被破坏，对光滑的聚合物表面单分子层 (SSML) 上的 DWC 进行了测试，显示稳定的热传递和液滴滑动一周的操作，得出聚合物层没有失效的结论。观察到纳米草的塌陷和断裂来解释 NGS 上随时间衰减的热传递。与 SSML 相比，NGS 的液滴离开尺寸更小，但传热系数更低，表明引入纳米结构后的正面和负面影响。提出了三种纳米结构失效机制。这项工作提出了纳米级流体壁相互作用的新研究领域。NGS 具有较小的液滴离开尺寸但较低的传热系数，表明引入纳米结构后的正面和负面影响。提出了三种纳米结构失效机制。这项工作提出了纳米级流体壁相互作用的新研究领域。NGS 具有较小的液滴离开尺寸但较低的传热系数，表明引入纳米结构后的正面和负面影响。提出了三种纳米结构失效机制。这项工作提出了纳米级流体壁相互作用的新研究领域。