Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
In Marangoni dropwise condensation, condensate drops move spontaneously when a bulk temperature gradient is applied to the condensing surface. It was considered that the velocity of drop movement is strongly affected by the horizontal component of Marangoni force around a condensate drop. And it is easy to infer that the horizontal component of Marangoni force is decided by both strength of Marangoni force and shape (angle) of condensate drop. In previous studies, it was shown that the velocity of condensate drop movement increases with the increase of bulk surface tension gradient and has a strong relation to initial drop distance. Initial drop distance was adopted as a parameter to express the characteristics of drop velocity, since the qualitatively relations among initial drop distance, Marangoni force and shape of condensate drop inferred from the previous experimental results. However, those relations are still not known clearly in detail. Furthermore, the mechanism on the condensate drop movement is also still not well understood. Therefore, in this paper, experimental study was carried out and the quantitative relation between initial drop distance and angle of condensate drop is investigated. In addition, numerical calculations on the condensation process of water-ethanol vapor mixture and the behavior of condensate were performed by using the VOF (Volume Of Fluid) method to qualitatively analyze the mechanisms of condensate drop movement.