Review of the dynamic Leidenfrost point temperature for droplet impact on a heated solid surface

Droplet impact on a high-temperature solid surface in the film boiling regime is widely encountered in various modern industrial and technological applications. The present article provides a systematic overview of the lower threshold of film boiling, the dynamic Leidenfrost point temperature, for a single impacting droplet. An extensive literature survey is conducted which includes both experimental and theoretical works. The first section of the review focuses on the parameter influences of the dynamic Leidenfrost point temperature, including impact conditions, surface characteristics, fluid properties, and the external environment. It is shown that, despite extensive prior work, there are many inconsistent conclusions regarding the effects of different parameters. Overall, contradictory experimental findings point to a need for future work using different types of fluids, and broad ranges of operating conditions and surface parameters. This is followed by a review of prior theoretical models which are derived using different fundamental hypotheses, including bubble nucleation theory, transient heat conduction, the vapor-gas layer analogy, and the pressure balance criterion, the majority of which are semiquantitative and rely on measured or simulated parameters for closure. In addition, measurement and modeling of the vapor layer thickness beneath an impacting droplet are discussed, which has a pivotal influence on the dynamic Leidenfrost phenomenon. It is concluded that future experimental investigations taking advantage of modern sophisticated imaging techniques are required to accurately capture the evolution and characteristics of the vapor layer. This information will play a crucial role in the development of a theoretical and experimentally-validated model for the dynamic Leidenfrost point temperature.