Visual Experiment On The Coalescence Of Liquid Drops On Homogeneous Surfaces

The coalescence between two drops on solid surface is an important phenomenon in dropwise condensation, which has significantly influences on the growth, the separation and the elimination of drops. Many researches showed that, the coalescence is the main reason to speed up the movement of drops on the surface with gradient surface energy and separate from the surface in dropwise condensation. Besides, it is also common phenomenon in the area of transmission process, such as chemical industry, environmental protection, and energy power, which play the very major role to the entire transmission process.In this paper, the coalescence between two drops on homogeneous surface in the atmosphere under constant temperature was observed and studied by using an ultra-fast camera. The effects of characters of surface and drops, inclination angle of surface and radius ratio of drops on the variations of the contact line, the bridge and the contact angle of drops with coalescence time were analyzed for the first time, and the comparison of coalescence between equal-size drops and non-equal-size drops was made. The behaviors in coalescence and its effects on the movement of drops were studied systematically and the mechanism of coalescence was also analyzed. Therefore, this research possesses high academic value and practical applicable value. The main contents of the dissertation are as follows:1. The two drops were injected out below the experimental surface, which could make the drops grow up slowly to coalesce. The experiment was conducted in this way for the first time.2. It was found that the drop behaved as a typical damped oscillation after coalescence as a result of differential pressure in concave convex liquid level of the two drops. The energy consumption resulted from viscous dissipation in process of internal flow within liquid drop was compensated by the released surface energy due to the decrease of drop interface area in coalescing.3. Visual experiments were conducted for studying coalescing process of two drops on surface of red copper and glycol, the results showed that the oscillation amplitude of bridge is higher, the oscillation of contact angle is more drastically and the oscillating time is longer than the latter when the two drops coalesced on surface of red copper.