水平表面水-酒精混合蒸气Marangoni瞬态凝结过程的凝结液形态

设计搭建了水平表面上凝结实验系统，利用高速摄像机对水-酒精混合蒸气Marangoni瞬态凝结过程的凝结形态进行观察记录，获得了初始过冷度、酒精蒸气浓度及蒸气流速对凝结形态的影响规律。采用图像边缘提取技术对凝结图像进行处理，统计得到了作为定量表征Marangoni凝结形态参数之一的最大液珠半径的变化规律。研究结果表明：凝结开始的一段时间内凝结形态变化剧烈，液珠经历形成、合并及逐渐长大的过程，最终凝结形态基本保持不变，液珠成长时间数量级约为10 s。在凝结的初始阶段，当过冷度较大时，膜状凝结与珠状凝结同时存在于凝结表面；随着过冷度降低，小液珠数目增多；过冷度继续降低，凝结面全部被大量小液珠所覆盖。随着初始过冷度降低、酒精蒸气浓度增高，凝结液珠成长时间增长，液珠的生长速度变慢。蒸气流速对液珠的成长过程影响相对不明显。随着凝结进行，最大液珠半径从2 mm增大到10 mm的数量级；同一凝结时刻，随着初始过冷度增加、酒精蒸气浓度降低，最大液珠半径逐渐增大。

Characteristics of Marangoni dynamic condensation modes for water-ethanol mixture vapors on horizontal surface

An experimental system was designed and built for condensation on a horizontal surface. Using the high-speed camera, the characteristics of Marangoni dynamic condensation modes for water-ethanol mixture vapors was investigated. The influence of initial vapor-to-surface temperature, ethanol vapor concentration and vapor velocity on the condensation modes was obtained. Using the method of edge detection to process the condensation pictures, the variation of maximum droplet radius, which was considered as an important parameter for quantitatively expressing Marangoni condensation modes, was obtained. The results showed that the condensation modes altered dramatically as condensation started. Then, the generation, merging and growing process of droplets could be observed until the condensation modes nearly kept constant. The order of magnitudes for the droplets growth time was about 10 s. On the beginning of condensation, when the initial vapor-to-surface temperature was high, filmwise and dropwise condensations were all on the surface. The number of droplets increased with the decrease of initial vapor-to-surface temperature. With the initial vapor-to-surface temperature kept decreasing, the surface would be covered by many small droplets. When the initial vapor-to-surface temperature decreased and ethanol vapor concentration increased, the droplets growth time would be longer, the droplets would grow slower. By contrast, the growth of droplets was slightly affected by vapor velocity. The maximum droplet radius increased during the condensation process and it would increase from 2 mm to more than 10 mm. At the same condensation time, the maximum droplet radius increased with the increase of initial vapor-to-surface temperature and decrease of ethanol vapor concentration.