The splashing phenomena of a liquid droplet impacting with a sessile droplet on a dry surface

This paper presents the results of an experimental study on the collision of a liquid droplet with a sessile droplet on a solid surface. In particular, the splash morphology for deionized (DI) water, 30% glycerol water, and ethylene glycol with an impact velocity in the range of 2.7 to 3.81 m/s was investigated. For the DI water and 30% glycerol water droplets, three different volume ratios of the sessile droplet to the falling droplet (V_s/V_o), i.e., 2.22, 3.44, and 4.92 were used, while two values were used for the ethylene glycol droplet, i.e., 4.3 and 5.7. It was found that the three liquids have three different splashing patterns due to the effects of surface tension and liquid viscosity, i.e., prompt splashing for DI water, delayed splashing for 30% glycerol water, and crown wall breakup splashing for ethylene glycol, respectively. It was observed that lower viscosity led to prompt splashing while lower surface tension led to crown wall breakup splashing. The prompt splashing and crown wall breakup splashing produced smaller secondary droplets, while the velocity of the secondary droplets during crown wall breakup splashing was higher than that during prompt splashing. The crown shape was similar to the three different liquids, which was a bowl shape, and the value of the sessile droplet volume had a great effect on the crown shape. Also, an empirical equation to predict the value of the maximum height of the crown was constructed. It was found that the maximum height of the crown strongly depended on the Weber number and also on the value of the sessile droplet volume for the DI water, 30% glycerol water, and ethylene glycol droplets.