Abstract Condensation is an important process in the Rankine cycle that significantly affects overall efficiency. Condensate typically forms a liquid film due to the high surface energy of industrial condenser materials; by engineering the condenser surface with a superhydrophobic layer, however, we can increase condensation heat transfer by an order of magnitude with the jumping droplet mode of condensation. While the basic phenomenon of jumping droplet condensation has been explored in depth, its effects on heat transfer and pressure drop in confined vapor flow inside a condenser tube, as in power plant condensers, have not been considered. Here, we report an experimental study of internal forced convective condensation with hydrophilic, hydrophobic, and superhydrophobic surfaces to study condensation in the filmwise, dropwise, and jumping droplet modes, respectively. The condenser tube samples were tested in a closed system internal flow condensation setup, and the heat transfer and pressure drop behavior were characterized over various operating conditions. In the jumping droplet mode, the heat transfer coefficient was highest at lower condensation heat flux and condenser surface subcooling, but a transition to the flooded mode at higher subcooling resulted in a heat transfer coefficient comparable to filmwise condensation. For dropwise condensation in the hydrophobic tube, the condensation heat transfer coefficient increased with the vapor velocity, similar to observations in past work. In addition to a large heat transfer coefficient, the pressure drop with the superhydrophobic tube samples was the lowest. These experimental results demonstrate the viability of harnessing the jumping droplet mode of condensation to enhance heat transfer and reduce pressure drop for internal forced convective flow condensation in industrial condensers.

中文翻译：

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内部对流蒸汽流中的跳跃液滴冷凝

摘要 冷凝是朗肯循环中的一个重要过程，对整体效率有显着影响。由于工业冷凝器材料的高表面能，冷凝物通常会形成液膜；然而，通过设计具有超疏水层的冷凝器表面，我们可以通过跳跃液滴冷凝模式将冷凝传热增加一个数量级。虽然已经深入探讨了跳跃液滴冷凝的基本现象，但尚未考虑其对冷凝管内受限蒸汽流中传热和压降的影响，如在发电厂冷凝器中。在这里，我们报告了具有亲水性、疏水性和超疏水性表面的内部强制对流冷凝的实验研究，以研究膜状、滴状、和跳跃液滴模式，分别。冷凝器管样品在封闭系统内部流动冷凝装置中进行了测试，并且在各种操作条件下表征了传热和压降行为。在跳跃液滴模式中，较低冷凝热通量和冷凝器表面过冷时的传热系数最高，但在较高过冷度下过渡到淹没模式导致传热系数与膜状冷凝相当。对于疏水管中的逐滴冷凝，冷凝传热系数随着蒸汽速度的增加而增加，类似于过去工作中的观察结果。除了大的传热系数外，超疏水管样品的压降最低。