Experimental investigation on impact and spreading dynamics of a single ethanol-water droplet on a heated surface

In the present study, the impact and spreading dynamics of a single droplet on a heated surface are exper-imentally investigated. Ethanol-water droplets with ethanol concentrations of 0-8 vol% are adopted as the working fluid with a wide range of surface temperature from 75 degrees C to 450 degrees C and the Weber number ranges from 7 to 63. The instantaneous droplet evolution after impact is studied via visualization. All the observed phenomena implied that ethanol additive has a significant influence on both impact dynamics and spreading characteristics. A new phenomenon is observed that the addition of ethanol can compensate for the negative influence of small Weber numbers, i.e., some ethanol-water droplets with smaller Weber numbers show better spreading dynamics, higher breakup and atomization possibility but weaker rebound compared with water droplets with higher Weber numbers. It is speculated that droplet impact is no longer solely dependent on the Weber number for ethanol-water droplet, and lower surface tension caused by ethanol additive and Marangoni effect due to concentration gradient along the interface are mainly responsible for this difference. The result also shows that impact behavior exhibits complex dependence on the surface temperature and Weber number, including deposition, rebound, rebound with atomization, breakup with atomization and breakup, while the regime map is significantly affected by ethanol additive. (c) 2020 Elsevier Ltd. All rights reserved.