Effect of iso-propanol additive on the impact dynamics of a Leidenfrost water droplet

Abstract

This paper experimentally investigated the Leidenfrost dynamics of an impacting droplet of water and 2–8 vol% iso-propanol-water solutions in the film boiling regime up to 450 °C. A single millimetric droplet was released from a height of several centimeters to yield different impact velocities. The aim of the present study was to clarify the influence of iso-propanol additive on the dynamic Leidenfrost point temperature, maximum spreading factor and nondimensional residence time, which remains to be verified. Visualization study with high-speed imaging indicated that the droplet impact pattern depends on both surface temperature and iso-propanol additive. It was shown that the dynamic Leidenfrost point temperature increases with impact velocity, and was significantly elevated with a small amount of iso-propanol additive by approximately 40 °C at the same Weber number. Especially, the lowest value of the mixture droplet with the smallest impact momentum (430 °C at 0.44 m/s and We = 6.2–8.3) still surpassed the highest value of the water droplet with the largest impact momentum (410 °C at 1.33 m/s and We = 55.0) within the present test range. Meanwhile, the iso-propanol additive markedly enhanced the droplet spreading ability, which was speculated to be caused by lower surface energy. Results also demonstrated that the nondimensional residence time was highly dependent on the impact velocity, but was not significantly influenced by the iso-propanol additive. Empirical correlations of the maximum spreading factor and nondimensional residence time were proposed with satisfactory predictive accuracy and good universality.