Experimental study of water drop motions induced by superposition of vibrations and shear flows

Abstract

Droplet motion induced by mechanical vibrations and superposed shear flows has not yet been investigated in detail, despite its major importance in many applications. The current study introduces a novel experimental setup for this purpose. Furthermore, droplet motion measurements on acrylic glass surfaces are presented. This study observes mechanical vibrations and shear flows separately as well as in combination. Measurements with sinusoidal vibrations show that the droplets overcome the force due to contact angle hysteresis, when vibrational acceleration is increased above a certain threshold. Consequently, droplets experience a lateral motion, particularly if the vibrational frequency matches their natural frequency. Separate experiments with shear flows indicate that droplet motions are initiated when a critical flow velocity is reached. The flow velocity required to initiate drop motions decreases when increasing droplet volume. Superposing vibration with the shear flow results in an inconvenient droplet contour and motion, the shaking slip motion. Additionally, the required flow velocity for droplet motion reduces noticeably. Furthermore, the influence of vibrations on the initial droplet motion increases with higher droplet volume. The study concludes that the mobility of water droplets on acrylic glass surfaces increases significantly when a superposition between vibrational forces and shear flows exists.