Evaporative and non-evaporative droplet impact on a heated phase change material pool: A comparison between ethanol, acetone, and distilled water

The interaction between liquid droplet and phase change material (PCM) underlies the direct contact approach, which is an efficient way for precipitating the melting and solidification processes of PCMs. In this experimental research, to comprehend the direct contact method more profoundly, the impingement of a single droplet on the heated paraffin pool, having a temperature of 70–95 °C, is scrutinized systematically for the first time. Droplet impact solidifies a portion of the pool and may lead to droplet evaporation. Acetone, ethanol, and distilled water are exploited as droplet liquids, whose diameter and impact velocity range from 2.32 to 3.36 mm and from 1.70 to 2.28 m/s, respectively. Through impact visualizations, six distinct regimes are observed, whose regime maps are constructed. Moreover, the effects of fluid properties, pool temperature, and the Weber number on the evolution of crater and jet, crater depth, crater shape, and solidified PCM area (A) generated after the impingement are investigated. It is ascertained that the low PCM temperature instigates the coalescence phenomenon regardless of the Weber number. Additionally, the crater depth is a function of the PCM temperature, Weber number, and Ohnesorge number; thus, a dimensionless correlation is proposed for the maximum crater depth. Furthermore, droplet evaporation augments the extracted heat from the paraffin, provoking a more sizeable solidified area. Interestingly, though absorbing the greatest amount of heat from the PCM, ethanol droplet generates a smaller solidified area than acetone since acetone favorably spreads on the pool surface, enhancing the effective heat exchange area.