Dynamic Behavior of Droplet Impact on a Superheated Particle Bed

Droplet impact on particles is a very common phenomenon in nature, industry, and agriculture. Nevertheless, the intrinsic physical processes involved in droplet impacts on high-temperature particles remain largely uncharted. In this study, the impact mode, fluidization characteristics, and dynamic behavior of droplet impact on a superheated particle bed are explored. The existence of the Leidenfrost effect is demonstrated through identifying the specific impact process. It is found that droplet impact on a superheated particle bed would exhibit three typical behavior modes, including spreading, contraction rebound, and immersion excavation. After the impact process, the particle bed would form various crater morphologies, which are described as doughnut structure, porous structure, and conical crater structure. The experimental results show that the maximum spreading coefficient is proportional to Weber number (We) while the crater diameter is negatively correlated with We. The larger the We, the smaller the crater diameter formed after impact. Furthermore, as the particle size increases, the fluidization of particles becomes increasingly impeded. When the droplet contacts the particles at the same temperature, there will be no particle ejection and excavation phenomenon. Ultimately, it has been demonstrated that the maximum spreading coefficient is solely dependent on the impact velocity of the droplet and is not influenced by particle temperature, particle size, or liquid volume. This research aims to deepen our comprehension of the interaction dynamics between droplets and superheated particles, which is crucial to the advancement of practical applications in this field.