Motion of adhering droplets induced by overlapping of gravitational and periodical acceleration
•Instabilities of adhering droplets initiated by harmonic mechanical surface vibration•Analyzed influence of wetting properties, droplet sizes, substrate inclination and excitation direction•Droplet dynamics are categorized into three regimes (oscillation, motion, separation)•Motion maps provide inf...
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| Published in: | International journal of multiphase flow Vol. 135; p. 103537 |
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| Main Authors: | , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier Ltd
01-02-2021
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | •Instabilities of adhering droplets initiated by harmonic mechanical surface vibration•Analyzed influence of wetting properties, droplet sizes, substrate inclination and excitation direction•Droplet dynamics are categorized into three regimes (oscillation, motion, separation)•Motion maps provide information about the individual regimes and phase transitions•A dimensionless threshold for the initiation of droplet motion was found
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°-105°) are used and surface vibration is applied separately in vertical and horizontal directions. The experiments comprise different droplet volumes (3-20 µl) and various plate inclinations (0°-30°) for a wide range of frequencies (20-250 Hz) and accelerations (5-300 m/s²). 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. |
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| ISSN: | 0301-9322 1879-3533 |
| DOI: | 10.1016/j.ijmultiphaseflow.2020.103537 |