Simultaneous multiple droplet impact and their interactions on a heated surface

Multiple droplet impact on a heated sapphire glass is experimentally investigated to compare the hydrodynamic behavior of single and multiple droplet cases employing high-speed imaging techniques. Experiments are performed for a wide range of surface temperatures (23 degrees C - 350 degrees C) and different Weber numbers. By using an image analysis software, the hydrodynamic behavior of the multiple droplets after the impact, uprising sheets and effective spreading areas are examined. Results indicate that, compared to a single droplet, the simultaneous impact of multiple droplets show rather different dynamics owing to the involved interaction phenomena. Besides, it is found that horizontal spacing and Weber number have strong effects on the effective spreading area and uprising sheet. The higher uprising sheet means the less spreading area and the less heat transfer from the heated surface. Furthermore, it is observed that for a larger horizontal spacing between the droplets, liquid lamellas lose more energy because of viscous dissipation and this causes forming weaker and delayed uprising sheet. In addition, increasing surface temperature decreases viscosity of the liquid causing more instabilities at the uprising sheet. Subsequently, uprising sheet smashes into several small pieces earlier since relative molecular motion is easier with increasing temperature. This paper introduces one of the limited experimental studies for the simultaneous multiple droplet impact on the heated surface and provides real-time high quality images and data.