School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an, 710049, China.
Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, 100190, China.
Sci Rep. 2017 Aug 17;7(1):8633. doi: 10.1038/s41598-017-09194-1.
In this work, we propose the concept to use the hydrophilic or neutral surface for condensation heat transfer and to use the superhydrophobic surface for enhancement by self-shedding and sweeping of condensate. Molecular dynamics simulation results show that no matter the vapor condenses on the solid surface in dropwise or filmwise mode, the grown-up condensate self-sheds and falls off the superhydrophobic surface, sweeping the growing condensate on the condensing surface downstream. We characterize the dynamics of condensate that the continuous self-shedding and sweeping effectively remove the droplets from the solid surface in dropwise mode or thin the condensate film on the solid surface in filmwise mode, which significantly enhances the condensation heat transfer. We reveal that the mechanism for self-shedding is two-fold: (1) that the external force on condensate bulk defeats the adhesive force between the condensate and the solid surface triggers the self-shedding; (2) the release of the surface free energy of condensate promotes the self-shedding. We also reveal that the mechanism of heat transfer enhancement is essentially due to the timely suppression over the growing condensate bulk on the condensing surface through the self-shedding and sweeping. Finally, we discuss the possible applications.
在这项工作中，我们提出了一个概念，即利用亲水或中性表面进行冷凝传热，并利用超疏水表面通过冷凝的自脱落和清扫来增强传热。分子动力学模拟结果表明，无论蒸汽以滴状还是膜状凝结在固体表面上，生长的冷凝物都会自脱落并从超疏水表面上掉落，从而将下游凝结表面上生长的冷凝物清扫掉。我们对冷凝物的动力学进行了特征描述，即连续的自脱落和清扫能够有效地将液滴从滴状模式下的固体表面上除去，或者在膜状模式下将薄的冷凝物薄膜从固体表面上除去，从而显著增强了冷凝传热。我们揭示了自脱落的机制有两种：（1）冷凝物整体所受的外力克服了冷凝物与固体表面之间的粘附力，引发了自脱落；（2）释放了冷凝物的表面自由能，促进了自脱落。我们还揭示了传热增强的机制本质上是通过自脱落和清扫及时抑制了在凝结表面上生长的冷凝物整体。最后，我们讨论了可能的应用。
