Dynamic Leidenfrost temperature of saturated water drops on textured surfaces

In this study, we propose an analytical model to predict dynamic Leidenfrost temperature for saturated water drops impacting on superheated smooth and textured surfaces. To define the Leidenfrost triggering mechanism, this model postulates a balance relation between the downward pressure by the drop itself and the resistant pressure arising from vaporization from the base of the drop; the former is expressed as the sum of dynamic and water hammer pressures induced by the drop motion while the latter is modeled with pressure buildup effect due to vapor flow within the thin film under the drop. The textured surfaces have uniformly distributed circular pillars with similar to 10 mu m length scale, and the center-to-center pitch of the pillars varies from 15 to 120 mu m. The experimental results show that the Leidenfrost temperature on textured surfaces increases at the same Weber number (We), as the pillar pitch becomes coarser. However, the Leidenfrost temperatures on the textured surfaces with relatively fine pitch were found to be rather lower than that on the smooth surface at the same We. Those experimental data are well predicted by the theoretical model, in which two simple equations with two unknowns (Leidenfrost temperature and thickness of thin vapor layer) are derived; one is based on the pressure balance relation and the other postulates an initial transient phase during drop impact. (C) 2020 Elsevier Ltd. All rights reserved.