Simultaneous double droplet impact on a molten phase change material pool: An experimental investigation

Abstract

Although momentous in numerous authentic applications, multiple droplet impacts on the liquid pool are overlooked in most studies. Hence, the impingement of simultaneous double ethanol droplets on the molten phase change material (PCM) pool, instigating the evaporation of droplets and the solidification of PCM, is comprehensively scrutinized for the first time. Experiments were carried out through high-speed imaging for various Weber numbers ranging from 179 to 464, pool temperatures from 70 to 95 °C, and several horizontal impact spacing. By altering impact parameters, five distinct regimes were observed in the case of double droplets. Based on observations, regime maps were also established for conducted experiments. Furthermore, the influences of the impact parameters on the central uprising sheet, formed between two impinging droplets, crater width, crater depth, jet height, and solidified PCM area, created after the impact was investigated. Additionally, the time evolution of crater width and depth was compared with the existing theoretical predictions. It was ascertained that boosting either the Weber number or the impact spacing intensifies the droplets' spreading areas, leading to a larger solidified PCM area, whereas temperature inversely affects this parameter. Moreover, increasing the impact spacing diminishes the central uprising sheet height and retards its formation, while raising the Weber number monotonously strengthens the central uprising sheet. The research, whose results have an immediate application in novel energy storage devices containing droplet–PCM interaction, fills the gap between droplet impact and energy storage.