Dynamic Leidenfrost behaviors of different fluid drops on superheated surface: Scaling for vapor film thickness

For an impact drop on a superheated surface, the dynamic Leidenfrost temperature, T_LF, depends on several parameters such as impact velocity, vapor layer thickness, and thermophysical properties of the fluids. In this letter, we derived a scaling formula for T_LF using the well-known balance relation between the pressures exerted by drop impact and evaporated vapor flow. As the T_LF scale intrinsically requires estimating the vapor film thickness δ_v, it should be scaled based on the consideration of relevant physics postulated on the impact drop and evaporated vapor. Thus, for proper scaling of δ_v, we considered the drop–vapor interface deformation by drop inertial and surface tension forces during initial impact of drop. Results showed that δ_v could be scaled with drop diameter D₀ and Weber number We. For drops with low We (<10), δ_v scaled to ∼D₀We^−1/4 and ∼D₀We^−2/5 for drops with higher We. The explicit scale for T_LF agreed well with present experimental data.