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首页> 外文期刊>Journal of Heat Transfer >Modeling and Optimization of Superhydrophobic Condensation
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Modeling and Optimization of Superhydrophobic Condensation

机译：超疏水性冷凝的建模与优化

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Superhydrophobic microlnanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding water droplets via coalescence-induced droplet jumping at length scales below the capillary length. However, achieving optimal surface designs for such behavior requires capturing the details of transport processes that is currently lacking. While comprehensive models have been developed for flat hydrophobic surfaces, they cannot be directly applied for condensation on microlnanostructured surfaces due to the dynamic droplet-structure interactions. In this work, we developed a unified model for dropwise condensation on superhydrophobic structured surfaces by incorporating individual droplet heat transfer, size distribution, and wetting morphology. Two droplet size distributions were developed, which are valid for droplets undergoing coalescence-induced droplet jumping, and exhibiting either a constant or variable contact angle droplet growth. Distinct emergent droplet wetting morphologies, Cassie jumping, Cassie nonjumping, or Wenzel, were determined by coupling of the structure geometry with the nucleation density and considering local energy barriers to wetting. The model results suggest a specific range of geometries (0.5-2μm) allowing for the formation of coalescence-induced jumping droplets with a 190% overall surface heat flux enhancement over conventional flat dropwise condensing surfaces. Subsequently, the effects of four typical self-assembled monolayer promoter coatings on overall heat flux were investigated. Surfaces exhibiting coalescence-induced droplet jumping were not sensitive (＜5%) to the coating wetting characteristics (contact angle hysteresis), which was in contrast to surfaces relying on gravitational droplet removal. Furthermore, flat surfaces with low promoter coating contact angle hysteresis (＜2 deg) outperformed structured superhydrophobic surfaces when the length scale of the structures was above a certain size (＞2 μm). This work provides a unified model for dropwise condensation on micro/ nanostructured superhydrophobic surfaces and offers guidelines for the design of structured surfaces to maximize heat transfer.
机译：用于滴状冷凝的超疏水微纳米结构表面近来受到了广泛的关注，因为它们具有通过通过在毛细管长度以下的长度尺度上的聚结诱导的液滴跳动而脱落水滴来增强传热性能的潜力。但是，要实现针对此类行为的最佳表面设计，需要捕获当前缺乏的运输过程细节。虽然已经开发了用于平坦疏水表面的综合模型，但是由于动态的液滴-结构相互作用，它们不能直接用于微纳米结构表面的缩合。在这项工作中，我们通过合并单个液滴的传热，尺寸分布和润湿形态，开发了用于在超疏水结构表面上逐滴冷凝的统一模型。开发了两种液滴尺寸分布，这对于经历聚结诱导的液滴跳跃并表现出恒定或可变的接触角液滴生长的液滴是有效的。通过将结构几何形状与成核密度耦合并考虑润湿的局部能垒，可以确定不同的新兴液滴润湿形态，Cassie跳跃，Cassie非跳跃或Wenzel。模型结果表明，特定范围的几何形状（0.5-2μm）允许形成聚结引起的跳跃液滴，与传统的平面逐滴冷凝表面相比，其总表面热通量增强了190％。随后，研究了四种典型的自组装单层促进剂涂层对整体热通量的影响。表现出聚结引起的液滴跳动的表面对涂层的润湿特性（接触角滞后）不敏感（<5％），这与依靠重力液滴去除的表面相反。此外，当结构的长度尺度大于一定尺寸（> 2μm）时，具有低促进剂涂层接触角滞后（＜2度）的平坦表面的性能优于结构化的超疏水表面。这项工作为在微米/纳米结构的超疏水表面上的逐滴冷凝提供了一个统一的模型，并为结构化表面的设计提供了指导，以最大限度地提高热传递。

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