Coalescence and migration of a droplet on a liquid pool with an inclined bottom wall

We experimentally investigate the curvature-driven migration and coalescence of an ethanol droplet on the free surface of an ethanol pool with an inclined bottom wall by employing a high-speed shadowgraph technique. Two distinct coalescence phenomena, migrating partial coalescence and multidrop pinch-off, in addition to the normal partial coalescence and complete coalescence are observed when the Weber number (We), liquid depth at the impact point (d(l)/D), and inclination angle (theta) are varied. The three-phase contact line (TPCL) formed by the air-liquid interface on the inclined bottom wall and its curvature near the TPCL cause these unique dynamics. The coalescence behaviors are clearly demarcated by the regime maps drawn in d(l)/D-We and theta-d(l)/D spaces. We found that the transition between partial and complete coalescence occurs atWe approximate to 10, regardless of liquid depth, and that, for theta = 18 degrees, the influence of the inclined wall is apparent for We > 2, which increases as the inclination angle increases.