Polymer heat exchangers have drawn attention due to their special characteristics such as flexibility, low weight, corrosion, and bio-fouling resistance, as well as their ease of manufacturing. However, since their thermal conductivity is low, they require a way to increase their heat transfer rate. We investigated the effect of modifying the surface wettability of polymer films on the heat transfer rate during the condensation process, both theoretically and experimentally. Condensed water formation on the film surface depends on the surface wettability control, and thus, hydrophilic or hydrophobic surfaces can induce film-wise or drop-wise condensation, respectively. Generally, the polymer surface shows a hydrophobic property due to the intrinsic C-C and C-H bonding of polymer frames. Here, we used four different types of polymer films, which have different thermal conductivity and controlled wettability properties, including polyimide film, polyimide film containing aluminum nanoparticles, and both films with super-hydrophobic treatment. The results show that nanostructured polymers with hydrophobic treatment have a 25% lower wetted area fraction than those without hydrophobic treatment, independent of the thermal conductivity of the polymer films. To compare the heat transfer rates, we designed a thermal resistance model considering vapor convection, vapor-water interfaces and curvatures, and conductions of the droplet, nanostructure, and polymer. We found that the convective thermal resistance dominantly affects the heat transfer rate and treated polymers showed over 200% higher total heat transfer than bare polymer.

中文翻译：

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表面润湿性变化对用于热交换器应用的纳米结构聚合物膜的影响

聚合物换热器因其柔韧性、重量轻、耐腐蚀、抗生物污染等特殊特性以及易于制造而备受关注。然而，由于它们的导热性低，它们需要一种方法来提高它们的传热率。我们从理论上和实验上研究了在缩合过程中改变聚合物薄膜的表面润湿性对传热速率的影响。薄膜表面冷凝水的形成取决于表面润湿性控制，因此，亲水或疏水表面可以分别诱导成膜或逐滴冷凝。通常，由于聚合物框架的内在 CC 和 CH 键合，聚合物表面显示出疏水性。在这里，我们使用了四种不同类型的聚合物薄膜，它们具有不同的导热性和可控的润湿性，包括聚酰亚胺薄膜、含铝纳米颗粒的聚酰亚胺薄膜以及两种经过超疏水处理的薄膜。结果表明，经过疏水处理的纳米结构聚合物的润湿面积分数比未经疏水处理的聚合物低 25%，与聚合物薄膜的热导率无关。为了比较传热率，我们设计了一个考虑蒸汽对流、蒸汽-水界面和曲率以及液滴、纳米结构和聚合物传导的热阻模型。我们发现对流热阻主要影响传热速率，并且经过处理的聚合物显示出比裸聚合物高 200% 以上的总传热。