Experimental analysis of the interaction of adhering droplets for different arrangement of droplets under the influence of flow and surface vibration

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Because of the effects of contact angle hysteresis, droplets can stick to surfaces until a critical velocity of the gas flow is reached (e.g. droplet on the visor of a helmet). If a vibration of the surface is superposed, a reduction of the critical velocity can be observed leading to a transport in flow direction. If more than one droplet is present, coalescence of the droplets can be observed leading to the creation of liquid films. The detachment of droplets and the creation of films is a function of (i) the arrangement of the droplets, (ii) frequency and amplitude of the surface vibration, (iii) droplet volumina, (iv) liquid properties and (v) wetting behaviour (surface tension, contact angles). The relation should be examined for droplets in different arrangements. This should be done in an experimental approach. For the experiments flow channels are used which are connected to an electromagnetic shaker to generate controlled surface vibrations. The evaluation and analysis of the droplet movement is done by optical methods (shadowgraphy and PIV).