Leidenfrost instability in a circular container and its suppression using a rod

Leidenfrost drops have demonstrated promising applications in, for example, drag reduction. However, large Leidenfrost drops may be unstable when their diameters exceed a critical value, leading to less control of such drops in their applications. In this work, through theoretical and experimental investigations, we explore the instability of a Leidenfrost drop in a circular configuration, as well as the suppression of this instability using a small rod. There are four findings. First, the diameter of the largest inscribed cylinder inside a rod-container configuration is the critical dimension to determine Leidenfrost instability. Second, in the cases of water and isopropyl alcohol, the threshold value of this diameter is 8.3λ ± 0.3λ, where λ is the capillary length of a liquid. Third, due to the specific interface profile between the liquid drop and the surrounding vapor layer, the threshold diameter of a circular container for the instability to occur is slightly larger than its counterpart in the corresponding Rayleigh-Taylor instability problem. Fourth and finally, placing a rod inside a circular container reduces the size of the largest inscribed cylinder in the container. If the diameter of this inscribed cylinder is below the threshold value, the instability inside the container is suppressed.