Motion of adhering droplets induced by overlapping of gravitational and periodical acceleration

This experimental work deals with the motion behavior of adhering water droplets under the influence of gravity and harmonic surface vibration. Two different substrates with moderate static contact angles (74 degrees-105 degrees) are used and surface vibration is applied separately in vertical and horizontal directions. The experiments comprise different droplet volumes (3-20 mu l) and various plate inclinations (0 degrees-30 degrees) for a wide range of frequencies (20-250 Hz) and accelerations (5-300 m/s(2)). Depending on the process parameters, the droplet shows different motion patterns: static oscillation, transversal motion and separation. The different regimes can be clearly segregated and are illustrated in motion maps. The analysis reveals that with increasing acceleration the droplet exhibits a chaotic contour deformation. It was found that depending on the frequency the droplet either starts to move or is decomposed in smaller droplets with increasing amplitude. The later one is called separation mode. Especially the transversal motion mode takes place predominantly in the range of the first natural frequency of the droplet due to the pronounced and characterized asymmetric contour deformation. Concerning droplet motion a stability limit, i.e. a threshold value for initiating droplet motion is found by a dimensionless empirical approach. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This experimental work investigates the motion behavior of adhering water droplets under the influence of gravity and harmonic surface vibration. Different motion patterns and regimes are observed based on various process parameters, such as droplet volume, plate inclination, frequency, and acceleration. The analysis shows that increasing acceleration leads to chaotic contour deformation of the droplet, while different frequencies may cause the droplet to either start moving or be decomposed into smaller droplets.