Leach R N, Stevens F, Langford S C, Dickinson J T
Physics Department, Washington State University, Pullman, Washington 99164-2814, USA.
Langmuir. 2006 Oct 10;22(21):8864-72. doi: 10.1021/la061901+.
Dropwise condensation of water vapor from a naturally cooling, hot water reservoir onto a hydrophobic polymer film and a silanized glass slide was studied by direct observation and simulations. The observed drop growth kinetics suggests that smallest drops grow principally by the diffusion of water adsorbed on the substrate to the drop perimeter, while drops larger than about 50 microm in diameter grow principally by direct deposition from the vapor onto the drop surface. Drop coalescence plays a critical role in determining the drop-size distribution and stimulates the nucleation of new, small drops on the substrates. Simulations of drop growth incorporating these growth mechanisms provide a good description of the observed drop-size distribution. Because of the large role played by coalescence, details of individual drop growth make little difference to the final drop-size distribution. The rate of condensation per unit substrate area is especially high for the smallest drops and may help account for the high heat transfer rates associated with dropwise condensation relative to filmwise condensation in heat exchange applications.
通过直接观察和模拟研究了水蒸气从自然冷却的热水储液器上逐滴凝结到疏水聚合物薄膜和硅烷化玻璃载玻片上的过程。观察到的液滴生长动力学表明，最小的液滴主要通过吸附在基底上的水扩散到液滴周边而生长，而直径大于约50微米的液滴主要通过蒸汽直接沉积到液滴表面而生长。液滴聚结在决定液滴尺寸分布方面起着关键作用，并刺激基底上新的小液滴的成核。结合这些生长机制的液滴生长模拟很好地描述了观察到的液滴尺寸分布。由于聚结起了很大作用，单个液滴生长的细节对最终的液滴尺寸分布影响不大。对于最小的液滴，单位基底面积的冷凝速率特别高，这可能有助于解释在热交换应用中与滴状冷凝相关的高热传递速率相对于膜状冷凝的情况。
