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.